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  1. 552 points
    Firstly, Welcome to Stargazers Lounge - the liveliest place in the Internet to discuss all aspects of astronomy, share pictures and observing reports, and find out what there is to see in the night sky. To ensure the Forum operates as smoothly as possible, we ask that you read and adhere to our Code of Conduct: Stargazers Lounge – Members Code of Conduct Before we start …. Use of our forums constitutes acceptance and agreement to our Forum Code of Conduct. If you do not agree to these terms, please contact a member of the Administration Team to have your account disabled. If you violate the Code of Conduct, we reserve the right to terminate all accounts belonging to you without prior notice. We prefer to advise users of inappropriate behaviour; however, flagrant and repeated violations of our CoC will result in a ban. Our failure to enforce this policy, for whatever reason, shall not be taken as a waiver of our right to do so at any time. 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  2. 326 points
    What Can I Expect to See? By Way of Introduction It’s a very easy mistake to make. You see those spectacular images of colour and shape which show the beauty of the Universe and just how fortunate you are to live within it and you think to yourself, perhaps a telescope will show me something similar? Time passes and one day you hear about some astronomical phenomenon that’s going to occur. You’ve read the reports in newspapers and seen something on TV about the breath taking sights in the superlative that will appear in the night sky. So you decide to ask about what telescope you should buy and from an astronomer’s natural enthusiasm and well meaning intention you are informed that telescope x, or p or q will give you the most fantastic and awesome views. And so you purchase your telescope. The clouds and rain pass, you set up with batted breath and at long last you take a peek at the night sky, and your heart sinks. The meteor shower wasn’t that promised firework display after all. The giant planet was the size of a pea in the palm of your hand, and the spiral galaxy, and the cosmic clouds of nebulae were mere smudges in various tones of bland grey. You feel let down, disappointed. Somewhere in your mind you expected to see these Hubble type images, at least a little colour on those huge cosmic galaxies and if you don't feel ripped off, then perhaps at least a little deceived. Some may argue that there ought to be a warning on every telescope box and advert and image: This Telescope Will Not Show You A View Like Those in Magazines or Taken by Camara. Others, perhap partkaking in the casual ideology of cynicism, will blandly inform you that such warnings are pointless. You don’t expect to buy a guitar with a sticker on it saying, ‘Buying this guitar will not make you play like Jimi Hendrix.’ Nor do you buy some perfume with a label saying, ‘Buying this perfume will not give you the sex appeal of Brad Pitt.’ But somewhere in this jumble there is a middle ground we can tread upon. Some words of advice we can offer up so that new comers of the future never have the occassion to feel unnecessarily deceived or ripped off in any manner. The Telescope The primary function of a telescope is not necessarily to make things look bigger but ultimately to concentrate more light to your eye. Distances are so vast in the universe that the more light a telescope can gather, the more powerful it is. This power makes the object brighter which makes it easier for you to see distance features. It is measured in terms of aperture whose light gathering capacity increases with the square of its radius. Typical beginner’s telescopes range from about 4” to 8” and the typical distance these little bits of glass and mirror are looking at is anything between a few hundred or so million kilometers to many millions of light years. And what you will see will depend on many factors. These include but are not limited to, sky conditions, the quality of your telescope and eyepieces and your own level of experience. It’s worth pointing out at this stage that in general, you’re not going to be viewing over 200x magnification. If the telescope box tells you otherwise, don't believe it for the simple twofold reason that average sky conditions don’t allow for this to happen and that many objects are so far away that if you up the magnification too much you’re simply making them too dim. Assuming that for now the first two factors (quality of optics and sky conditions) are out of your immediate control, then a lot of what you are able to see in the night sky depends on your own observing skills and this requires time and patience. Typically, a beginner wants to see a bit of everything: The Moon, some planets, galaxies, emission and planetary nebulae, globulars and open clusters. The first part of this thread will concentrate on typical solar system objects viewed by the beginner. The second part will concentrate more on Messier objects and other deep space phenomena. Part I - The Solar System with 4" to 8" The Moon - you should be able to make out typical lunar features such as craters and riles. An 8” should be able to tweak out details about 2 to 3km in size. Bigger the aperture, brighter the image and the more detail you will see. Mercury and Venus - you’re going to see these planets as small disks, a lot bigger than the brightest stars but they will generally have a total lack of detail to be seen and you will only be able to observe their phases. Mars – again, you’re going to see this as a small red disk and if you want to see anything else you’re going to have to not only spend a lot of time at the eyepiece, but also have realtively high magnification which in turn requires some decent atmospheric conditions. After time, you might be able to make out a tiny white-ish area at its pole, perhaps a tiny dark marking or two. And all this in an object no bigger than a lentil in the palm of your hand. Jupiter - a 4" will reveal some detail on Jupiter and an 8" will reveal more. But in either case you need time to observe. If you look casually through the 4 or 8", have a quick five minute gander, you'll say to me in both cases, 'I saw a white-creamy disk about the size of a pea with one or two orangy-brown bands on it.' And yes, that is the first impression we'll all get, but to go beyond that you will need to work. An 8” will reveal a significant amount of detail but you need to sit quietly for quite some time, relaxed in a comfortable position and allow your eyes to respond to the faint delicate markings, the subtle whisps of differing shades which are present on the Jovian disk. You’ll also see the four big Jovian moons which will look like very bright stars. Visual observing is quite hard work but the more you do it the better you get and the more you see. Saturn – a similar story unfolds for Saturn. There are no easy wins in astronomy and you need to take your time. With a 4” to 8” telescope you should be able to see the rings of Saturn (it may just appear as the one), subtle bands on the planet itself, four or five of its moons that in some cases will appear like brightish stars and on a good night, Cassini’s Division which will look like a thin black circle drawn inside the rings. Uranus and Neptune – these will appear as tiny objects. With enough magnification you might be able to garner a pale blue or greenish colour and the appearance of a disk-like shape. The Sun – with the proper white light filters in place you will see sunspots and the structure within, namely, Umbra and Penumbra; you will see faculae, granulation and limb darkening. Do not ever look at the Sun without proper filtration. An Approximation of an Eyepiece View Here are some approximations of what you might see through your eyepiece which will hopefully ground expectations. Jupiter as taken by Voyager 1. Jupiter as seen in a 4" frac. Saturn as seen by Cassini. Saturn as seen in a 4" frac. Uranus a taken by Voyager 2 Uranus as seen through a 4" frac. I hope this part of the thread has helped a little in getting an idea of what to expect from your telescope. The second part will follow shortly dealing with some of the more popular Messier and NGC celestial objects. What Can I Expect to See...Galaxies and Nebulae A Truism or Two There’s an old truism that runs around the boards: a galaxy or a nebula is a faint, grey fruzzy in a 4” and a 6” and a brighter grey fuzzy in an 8” or a 10”. There’s also another truism which rings truer to an astronomer’s heart beat. All things being equal, you will see more tomorrow than you did today, and so it follows that you will never see less than you did this evening. Each evening with a galaxy or nebula you are training your eye and brain to notice more than what you have already seen. And that takes time; it takes patience, a little love and care at the eyepiece. Size, Magnitude & Brightness When beginning to observe deep space object such as globulars, galaxies and nebulae it is handy to bracket them into three intertwined classes: The size of the object The object’s magnitude And its surface brightness We do this so as to have a rough estimate of how well we may be able to view a given object, and by doing so not only arming ourselves with useful knowledge, but also lessening the impact of frustration and disappointment. Size As a frame of reference, we can argue that the angular diameter of the full Moon viewed from Earth is about 0.5 degrees, or 30 arc minutes, or 1,800 arc seconds. So a galaxy like M 31 is over 3 degrees in diameter. An emission nebula like M 42 in Orion is over 1 degree in diameter. A globular cluster like M 13 is about 16 arc minutes in diameter and a planetary nebula like M 57 is just over 1 arc minute. Apparent Magnitude The object’s magnitude is the total sum of all the light stemming from the object. There are differing ways this can be measured but for the observer the most useful guide would be the apparent magnitude. This scale starts on the minus side for bright objects and travels up into the plus side for dimmer objects. Most of the stars you see making up a constellation’s pattern have an apparent magnitude of about 1 or 2, M 31 about 3.5, M 42 around 4, M 13 about 5, M 57 about 8 and at a dark site the naked eye should be able to see stars down to about 5 or 6. Looking just at these figures, then, it would appear that M 31 and M 42, for example, are a lot easier to see than M 13 or M 57. But this is where it may get confusing. Surface Brightness If we say that the object’s apparent magnitude suggests the the overall light output of an object, then by comparison surface brightness is a measure of how bright an object may appear. Although it isn’t necessary for the given discourse, we can point out that apparent magnitude is not measured in any unit but surface brightness is actually measured in magnitude per square degree. Again, lower the number, brighter the object. M 31 has a surface brightness of about 23, M 42 around 22, M 13 about 21 and M 57 about 18. Looking at these figures, then, contrary to what we have just said, it now seems that M 13 and M 57 will be easier to see. So what gives? For something like M 31, although its apparent magnitude is relatively quite high making it one of the brightest deep sky objects in the night sky, its light is spread over a colossal area, that light is being thinned out and so the galaxy is very dim to see. By comparison, M 57 or M 13, although having a poorer apparent magnitide, are a lot smaller so the light, the magnitude per square degree, is more concentrated and therefore they have a higher surface brightness making them easier to see. Rule of Thumb As a general rule thumb, then, we can say that apparent magnitude is a good indication of how well you may see an object where we are dealling with point sources of light such as planets or stars, but for large extended objects such as globulars, galaxies and nebulae, surface brightness and size are the tools you want to be using. Take this as an indicative, not a definitive rule of thumb. Other Factors to Bear in Mind No matter what has just been said above when it comes to observing deep space objects most of what you will be able to see will depend on a myriad of other factors, not limited to, the quality of your optics, atmospheric conditions and inevitably, your own experience. Nevertheless, we can suggest a number of pointers to bear in mind when preparing for a deep space session: Dark skies Whereas planets and the moon are bright and largely unaffected by light pollution, being large and extended and very faint, deep space objects depend entirely on dark skies. If we say that a comfortable seat will add ½” to 1” of aperture to your telescope, then the impact of dark skies is unprecedented. It’s probably not much of an exaggeration to say a 6” under dark skies will blow away a 10” or 12” in an urban setting. Galaxies and nebulae and globulars are some of the faintest deep-sky objects and dark skies are everything when viewing them. Transparency Whereas good seeing conditions are essential to good planetary and lunar observing, deep space objects are more dependent on clear, transparent skies. Magnification Whereas detailed planetary and lunar observing require high magnifications, there's no ideal magnification in which to view deep space objects. It’s a case of trial and error. If you want to view M 31 in its entirety, you’ll need extremely low powers but if you want to see a little more detail, you will need magnification. Some planetary nebulae, some globulars take magnification well, some don’t. It’s a case of trial and error. Filters Whereas colour filters aren’t really that useful when viewing planets, nebulae often benefit from filters, in particular, narrowband ones like UHC and OIII filters. They improve contrast and make faint details apparent. There aren’t filters to improve your views of galaxies and even if there were, any improvement would be negligible. An Approximation of an Eyepiece View Here are some approximations of what you might see through your eyepiece. Bear in mind that the sketches were generally not made in a hurry and in many cases took a good hour or so sitting at the eyepiece. M 31 - Galaxy. Hubble Image. M 31 - 4" Sketch. M 51 - Galaxy. Hubble Image. M 51 - 4" Sketch. M 27 - Planetary Nebula. Hubble Image. M 27 - 4" Sketch. M 3 - Globular Cluster. Hubble Image. M 3 - 4" Sketch. M 42 - Emission Nebula. Hubble Image. M 42 - 4" Sketch I hope this had helped a little. - - - - - - - - P.S: Thank you everyone for your kind replies and support. I'm sorry I haven't replied to each of you but it's been a busy day and I just haven't had the time. Seriously. Please don't think me rude and I will make ammends this weekend. I will try to post up a little on open clusters and doubles with a shorter and final third part. Thank you again to everyone
  3. 163 points
    I have considered the question of what a person needs in his eyepiece kit, as a bare minimum, for quite a while. Personally, I don't have a lot of disposable income, and I recognize that a lot of amateur astronomers are getting along on a shoestring budget. So, if you can afford to go out and buy a full set of Naglers, or even Radians, go ahead, this article isn't for you. It is for those of us who have to choose between a new eyepiece and a new spring jacket, and are already garnering disapproving looks from our partners for buying that natty little refractor at a higher price than they really, truly expected. I will talk first about scopes on equatorial or tracking mounts, and later about Dobsonians. I am assuming that, as we don't have a lot of money, we are not buying large catadioptics or refractors, and cannot afford a Newtonian of larger than 8". These general principles apply to most scopes, however. SCOPES ON EQUATORIAL, GOTO, OR TRACKING MOUNTS I am going to talk about Plossls, mostly, as they are the best value for money. If you get a branded Plossl, you will seldom get a piece of junk. You can expect reasonable sharpness across most of the field in all but the fastest scopes. Plossls also have a field of view of 50 - 52º, which is quite reasonable. I am also going to suggest a set of three or four eyepieces, and no Barlow,except in the case of a fast scope. You should have a high power, a medium-high and/or medium-low power eyepiece, and a low power eyepiece. The eyepieces that came with your scope probably fill the medium-high and low power slot. If they are satisfactory, keep them for now. If they are marked 'H' or 'SR' don't even think about keeping them! If they are marked with a 'K', they are Kellners, which are generally acceptable eyepieces, but a little limited on field of view, being about 45º, usually. Find out the focal ratio of your scope. It should be printed on a plate on the scope, usually near the focuser, and be represented by a number like f/5 or f/8. F/6 or lower is a fast scope, and f/7 or higher is an intermediate to slow scope. Scopes with focal ratios of f/8 or higher are generally more forgiving of lower-quality eyepieces, while fast scopes tend to reward lower-quality eyepieces with fuzzy stars anywhere from 1/3 to 1/2 way from the edge to the centre. If you can't find the focal ratio, but you know the aperture and focal length, the focal ratio is (focal length/aperture). Take your focal ratio, and multiply it by 3/4. So, if you have an f/8 scope, the result is 6. If you have an f/10 scope, the result is 7.5. This result is the length in millimetres of your high power eyepiece. It will give about 2/3 of the theoretical maximum power of your scope. This is the actual maximum if you do not always enjoy perfect seeing and transparency. If you have a 100mm scope, this eyepiece will give 133x. IF YOU HAVE A FAST SCOPE, say, f/5, this formula will suggest a 3.75mm or 4mm eyepiece. Looking through a Plossl at this length is a miserable experience. If this is the case, I would suggest you buy an eyepiece with a length equal to 1½ times your focal ratio, and buy a 2x Barlow lens in the same price range as your eps. These purchases give you your high power and medium-high power magnifications, so skip the next paragraph. Now multiply your focal ratio by 1¼. For our f/8 scope, the result is 10, and for an f/10 scope, the result is 12.5. This is the length of your medium-high power eyepiece. For our 100mm scope, it gives a magnification of 80. Eyepieces in these lengths are not hard to find, and you can go up or down a millimetre if your dealer doesn't stock them. Multiply your focal ratio by 2, now. By now, you can do the math yourself! In our 100mm scope, this gives a magnification of 50. This is your medium-low power eyepiece, and your low power eyepiece is given by multiplying your focal ratio by 3, and you get a magnification of 33 in your 100mm scope. IF YOU HAVE A FAST SCOPE, you want an eyepiece of 3 to 4 times your focal ratio, or 15 to 20 mm for an f/5 scope as your medium-low power eyepiece, and about 5 times your focal ratio for your low power eyepiece. An eyepiece of 5 times your focal ratio also gives you an 'exit pupil' of 5mm. This is the longest eyepiece you want to use if you are older, as this exit pupil is approximately equal to an older (45+) person's maximum pupillary dilation. You can't use more light than that. If you are younger, you could go up to 7 times your focal ratio, or an exit pupil of 7mm. To summarize, for an f/8 scope, we suggest a kit consisting of 6, 10, 16 and 24mm. For an f/10 scope, 7.5, 12.5, 20 and 30mm. For an f/5 scope, 2x Barlow, 8, 18, and 25mm. If your budget allows for only three eyepieces, drop one of the medium power eyepieces. If you are a lunar/planetary observer, then we would suggest dropping the medium-low eyepiece, and if you are a DSO observer, the medium-high eyepiece. In the latter case, we could suggest dropping the high power, but let's face it, there will always be times you want to get a good look at Saturn, or a good planetary nebula, so keep the high power. DOBSONIANS Dobsonians tend to be large, fast scopes. If your Dob is 6" or less, you can safely follow the guidelines for the scopes listed above, as the highest magnification this will give you is 200. At about 200x, it gets hard to follow things with a Dob. Some people can do it, and your ability to follow objects will improve with time, but 200x is a good start. You will want to have an eyepiece kit between 200x, and a 5mm (or 7mm if you are a youngster) exit pupil. Suppose you have a 10", f/5 Dob. You will have a focal length of 1250mm, and will get 200x with a 6.25mm eyepiece. In practical terms, a 6.5 to 7.5mm eyepiece will be what you will find available. To get a 5mm exit pupil out of a 250mm mirror, you will need an eyepiece that gives you 50x. This means a 25mm eyepiece. To get a 7mm exit pupil out of the same mirror means a magnification of 36, and a 35mm eyepiece. Having decided on your low and high power, it is fairly easy to pick two more eyepiece focal lengths that will fill in the gap. If your spread is 6mm to 25mm, try 10mm and 16mm as your intermediate lengths. If the spread is 6mm to 35mm, then use 12mm and 20mm as your intermediate eyepieces. So, for an 8" f/5 Dob, you would be getting something like a 5mm, 10, 16 and 25mm. These guidelines will give you a useful set of eyepieces without breaking the bank. You can buy one eyepiece a month until you have your set, and use the eyeieces you have until your set is complete.If you can afford slightly better eyepieces, then buy those, with the length guidelines still in mind. If you have a fast scope, ask specifically if the eyepiece you are considering is appropriate for a fast scope. Some less expensive wide-angle eyepieces perform well only in a f/8 or slower scope, and you don't want to buy a set of these with a fast scope. Best wishes, and enjoy your new hobby!
  4. 154 points
    Hi guys!I finally managed to decide I'm done processing my insane photoproject of digging deep inside M31.Long story short: One picture of M31, 27megapixel 2x2 mosaic, +3 months of imaging in crappy weather, 18 separate nights, 534 separate exposures, +150 hours of processing, 1233 manually annotated objects inside M31.(images in the end of this post, lots of "bla bla" first)I had a great start last autumn with loads of clear nights, which made me think it be a quick stab to make a 2x2 mosaic (my first mosaic btw) of M 31 since my f.o.v is to narrow to capture M31 in one frame...But pretty much as soon as I started, the swedish weather turned into a mess which made me shoot M31 during 18(!) separate nights, during more than 3 months(!).I also spent countless of hours studying the M31 Atlas available online at: http://ned.ipac.caltech.edu/level5/ANDROMEDA_Atlas/frames.htmlIt contains +40 annotated plates of M31 captured with Kitts Peak 4m telescope and contains +1000 globular clusters, open clusters, stellar ascossiations and dust-clouds inside M31.By looking at those charts, I manually annotated 1233 objects in my image, along with names & outlines (except for dustcloud-names, since it cluttered the image too much)Here's what I found within my image:232 Globular Clusters235 Open Clusters140 Stellar Assosciations626 Dust CloudsData captured using ACP + SchedulerCalibration was done in Maxim, registration & stacking + mosaic-merging done in PI, the rest in photoshop.Gear:Telescope: Orion Optics AG12Camera: QSI 583 wsg-8Mount: 10Micron GM 2000 HPSGuiding: UnguidedSummary of exposures:Lum: 364 x 180s / 1092 minutesRed: 39 x 300s / 195 minutesGreen : 36 x 300s / 180 minutesBlue : 43 x 300s / 215 minutesHa : 52 x 900s / 780 minutesTotal time: 2462 minutes / 41 hoursHere are a few 100% crops so you can appreciate the level of resolution and the hard work behind it.(note Hubbles famous Cepheid, marked as "Var 1")Also, here's one of the charts used for annotation along with a matching crop from my image:If you're not using a mobile device, I highly recommend following the links to my homepage where the image is presented in full resolution along with selectable annotation-layers containing the following:Globular ClustersOpen ClustersDark NebulaeStellar AssociationsGrid + DSO'sIt was really mind-boggling processing a image of this scale, realizing that all those fuzzy spots visible inside the galaxy are actually open clusters and globular clusters, along with Ha-regions and much more!Unfortunately mobile devices usually downscale the huge 27MP resolution images and have trouble with the annotation-layers, so if you're using a computer(highly recommended), click the following images to be taken to my homepage where you can select which layers of annotation to be displayed, as well as the choice of 3 different resolutions. Otherwise there are direct-links to all versions below the images in this thread.Direct-links to images, No annotation:http://www.grinderphoto.se/pics/Med_102.jpg - (1024px width)http://www.grinderphoto.se/pics/Large_102.jpg - (3500px width)http://www.grinderphoto.se/pics/Full_102.jpg - (+6000px width)Direct-links to images, Annotated:http://www.grinderphoto.se/pics/Med_102_Annotated.jpg - (1024px width)http://www.grinderphoto.se/pics/Large_102_Annotated.jpg - (3500px width)http://www.grinderphoto.se/pics/Full_102_Annotated.jpg - (+6000px width)Thanks for watching, I hope you enjoy exploring all the details in this fantastic galaxy!Best RegardsJonas Grindehttp://www.grinderphoto.se
  5. 144 points
    ORION. This is a marathon O'Donoghue-Penrice production owing more to Tom than to me. Tom began the luminance and Ha in Spain four years ago using one Tak 106N/Atik 11000. We then set up the dual Tak rig here and carried on, finishing the colour and Ha acquisition a couple of weeks ago. (Running three Taks and three full frame cameras we collected 24 hours of data in two memorable nights!) Tom did the stitching of the part-stretched data and handed a copy over to me, so the final processing here is mine though Tom's own version is in the pipeline. Higher resolution data has been added from the TEC 140 to enhance M78, the Horse, Flame, Running Man and M42. It's a thirty panel mosaic weighing in at 1.03 Gig in Tiff format and covering nearly 270 million pixels. A full size print would be nearly 8 metres high, which is the whole point, really. We'd like to find a corporate buyer or museum interested in funding such a vast print. Exposure time is over 40% longer than the Hubble Deep Field at about 400 hours (AKA 1.44 million seconds or just over 16 days. ) Thanks also to Yves for the use of his camera when we had three Taks on the job or when mine was tied up on the TEC. We cannot link to a very large version because of the risk of theft so this is little more than a thumbnail to give the idea of the beast. We're sorry about that but with so much time invested we have to be careful. At full size M42 alone fills the screen. Just to reiterate, Tom's contribution exceeds mine on this. We hope you like it. Tom and Olly Link to a bigger one here: http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-LgK642h/0/O/ORION%20400%20HRS%20WEB.jpg
  6. 97 points
    By using stargazerslounge.com you agree to our use of cookies as described in this Cookie Policy. WHAT ARE ‘COOKIES'? Cookies are small text files which are downloaded to your computer or mobile device when you visit a website or application. Your web browser then sends these cookies back to the website or application on each subsequent visit so that they can recognise you and remember things like user details or user preferences. Cookies are very useful and do lots of different jobs which help to make your experience on websites as smooth as possible. For example, they let you move between web pages efficiently, remembering your preferences, and generally improving your experience. They are referred to as session or persistent cookies, depending on how long they are used: Session cookies only last for your online session and disappear from your computer or device when you close your browser. Persistent cookies stay on your computer or device after the browser has been closed and last for the period of time specified in the cookie. These persistent cookies are activated each time you visit the site where the cookie was generated. WHICH COOKIES DOES stargazerslounge.com (SGL) USE AND WHY? When you use our forum, the following 2 categories of cookies may be set on your device: 1. ‘Strictly necessary' cookies These cookies are essential in helping you to move around our websites and use their features, Clicking on the remember me button when logging in will set such a cookie. These cookies do not gather information about you that could be used for marketing or remembering where you've been on the internet. 2. Functional cookies These cookies allow websites and applications to remember choices you make (such as your user name, language or the region you are in) and provide enhanced, more personal features. The information these cookies collect is usually anonymised which means we can't identify you personally. They do not gather any information about you that could be used for selling advertising or remembering where you've been on the internet, but do help with serving advertising. We use these types of cookies to improve your experience on SGL. Some examples of how we do this include: Remembering the last time you logged in. Managing cookies in your browser Most modern browsers will allow you to: See what cookies you've got and delete them on an individual basis. Block third party cookies. Block cookies from particular sites. Block all cookies from being set. Delete all cookies when you close your browser. You should be aware that any preferences will be lost if you delete cookies. Ironically, this includes where you have opted out from cookies, as this requires an opt-out cookie to be set. Also, if you block cookies completely many websites will not work properly and some functionality on these websites will not work at all. We do not recommend turning cookies off when using our stargazerslounge.com. If you are primarily concerned about third party cookies, you can turn these off separately. The links below take you to the ‘Help' sections for each of the major browsers so that you can find out more about how to manage your cookies. Internet Explorer http://support.microsoft.com/kb/196955 Firefox http://support.mozilla.org/en-US/kb/Cookies Google Chrome http://support.google.com/chrome/bin/answer.py?hl=en&answer=95647 Opera http://www.opera.com/browser/tutorials/security/privacy/ Safari http://docs.info.apple.com/article.html?path=Safari/5.0/en/9277.html Safari iOS http://support.apple.com/kb/HT1677 Android http://support.google.com/mobile/bin/answer.py?hl=en&answer=169022 Blackberry http://docs.blackberry.com/en/smartphone_users/deliverables/32004/Turn_off_cookies_in_the_browser_60_1072866_11.jsp Windows Phone http://www.microsoft.com/windowsphone/en-us/howto/wp7/web/changing-privacy-and-other-browser-settings.aspx
  7. 85 points
    Pleas for help with PHD guiding seem to come up more often than almost other imaging topic. I make no claims to be the ultimate expert on the subject, but I have travelled some way along the road from guiding failure to success, and so I thought it might be good to share a few pointers I've picked up along the way. (By failure I mean I was getting one 1 minute exposure out of every five where the stars were slightly less egg-shaped than the rest. By success I mean I now discard one 10 minute exposure out of every thirty due to a guiding issue). Firstly, I am going to cover the basics of a good guiding set-up, since many problems that are blamed on PHD are actually external issues related to the equipment being used or abused. After that I’ll take a look at how to diagnose and fix guiding problems with PHD. Why Guide? If you are imaging DSOs, you will inevitably be drawn to the idea of guiding in order to be able to make longer exposures. That said, if you aren't ready to invest in a guiding rig yet, you certainly can improve your exposure length by better polar alignment and by using Periodic Error Correction (PEC) if your mount supports it. Eventually you will reach the limits of what is possible, or more likely the limits of your patience due to the amount of effort required before you can start imaging. Personally, I skipped the middle bits and went straight to guiding! Polar alignment of my NEQ6 mount consists of putting the tripod on some painted marks on the patio and spending five minutes using EQMOD and the polar scope to do a rough alignment. I don’t drift align and I don’t use PEC; I rely on my guiding rig entirely. As we will discover, the longer the effective focal length of your imaging scope, the more likely it is you will also need to get good polar alignment, to use PEC as well as guiding, or drop five or ten grand on a new mount! That said, using a short focal length scope on a decent mount and with an effective guider makes the mysteries of polar alignment and PEC a lot less important when starting out. Do I Really need Two Cameras? You cannot image and guide at the same time using one camera. The guide camera image needs to be read-out every few seconds to spot when guiding corrections are needed. The imaging camera needs to take a long exposure, and reading out the image ends that exposure, so you can’t do both at once! The only exceptions are self-guiding cameras, which consist of two cameras in one housing (see below), and some old cameras where one set of pixels was read out for guiding and another set used for imaging. The latter type wasn't particularly successful and I don’t think you can get them any more. There are many cameras on the market that can be used for guiding. Many people start by experimenting with webcams. These can work if your guide scope has a particularly fast focal ratio, but the lack of a long-exposure feature usually means you will be looking for a proper guide camera fairly quickly. If you are a planetary imager, you may already have a colour planetary camera; provided it can be set to take long exposures of at least a few seconds in duration and has an appropriate driver for PHD (or other guiding software), it will work as a guide camera, Alternatively you can buy a dedicated mono guide camera for between £100 and £150; keep an eye on the second hand market as these come up for sale regularly. The final option is an auto guider, which tend to be more expensive than the cameras above. The advantage of an auto guider is that you do not need a laptop to guide; all the brains are built into the camera and guiding commands are sent via the ST4 port to the mount without a computer involved**. I haven’t used an auto guider but reports of their success tend to be mixed; either they work or they don’t, and if they don’t it can be hard to diagnose the issue. On the plus side, most auto guiders can also be used as a ‘dumb’ guide camera in conjunction with PHD or other software. ** Note that not all cameras with a built in ST4 port have auto-guiding capabilities, so check the specifications. How to Choose the right Guiding Set-up There are three basic methods of guiding with various pros and cons: 1. Using a separate guide-scope and guide camera. A second, cheap telescope or finder and a cheap(ish) guide camera is mounted piggyback on top of the imaging scope, or side-by-side using a dual bar. Pros: Relatively cheap to purchase. Quick and easy to set up and use. Two telescopes on one mount looks really cool, like some kind of awesome space cannon. Cons: Flexure, mirror shift, flexure and flexure. When to use: On lower end mounts like the HEQ5, NEQ6 and cousins, a separate guide scope works best with shorter-focal length scopes. 2. Using an off-axis guider (OAG). An OAG sits between the focuser and the imaging camera. It uses a small prism to deflect part of the incoming light into the guide camera. Pros: Relatively cheap to purchase. Much less weight on the mount as there is no second scope. Reduces problems with flexure and mirror shift. Cons: Some people swear by OAGs, others swear at them. They have a reputation for being fiddly to set up and use for beginners, as you must get both the main camera and the guide camera parfocal and also locate a suitable guide star by moving and rotating the prism. When to use: A better option for long focal length scopes, and a much better option for moving-mirror scopes like SCTs. 3. Using a self-guiding imaging camera. A camera with a main imaging sensor, and a second (smaller) guiding sensor next to it. Pros: Much less weight on the mount as there is no second scope. Reduces problems with flexure and mirror shift. Much easier to set up than an OAG. Cons: Only a few higher end (expensive!) CCD cameras available. When to use: A better option for long focal length scopes, and a much better option for moving-mirror scopes like SCTs. Exposures Deeper than your Pockets? If you are just starting out in deep-sky imaging, it is important to realise than long-focal length imaging is hard on low-end mounts. Very hard. Don’t be fooled by all those glossy adverts in the magazines, anything in the sub £2,000 bracket is definitely low-end. Don’t take that remark the wrong way! Mass-market GOTO mounts have made deep-sky imaging accessible to us mere mortals, but understanding the capabilities and limitations of your equipment is key to success in this game. The first tip is to learn your craft using a short focal-length, fast f-ratio scope. Guiding is much easier, and you’ll get better results with shorter exposures (a virtuous circle). Aim for a focal length of no more than 800mm and an f-ratio of no more than f/6 (and if you have the budget to get to f/5 or f/4 with decent optics, so much the better). If you have an existing longer-focal length scope you might use a focal reducer, or if you are looking for a new scope, invest in a mid-range refractor (the ubiquitous Skywatcher 80ED with the matching 0.85x focal reducer/flattener is where many people start out, but there are many similar models to choose from at a variety of price points from reasonable to eye-watering!) I learned lesson this the hard way. I started out with lunar and planetary imaging through an ancient 8”, f/10 SCT (a relic of the pre-GOTO age). The 2,000mm of focal length was great for that sort of thing, but as I soon discovered when I purchased a shiny new NEQ6, it isn't so great for learning how to do deep-sky imaging: - 2,000mm is probably approaching (if not beyond) the limit of what an NEQ6 can track in the hands of an expert imager with years of experience. In the hands of a beginner like me, results were frustratingly poor and I wasted many nights getting nowhere fast. - f/10 is very slow for DSO imaging, necessitating long exposures. But long exposures were not possible (see above). A vicious circle not a virtuous one. Minimise Weight All mounts will quote a maximum weight that they can carry. Firstly, check whether the quoted weight is just that of the scope and other equipment or whether it also includes the counterweights (which has been the case in some more dubious marketing materials). The next tip is that once you know the maximum equipment carrying weight of your mount, divide it in half. That is the target weight for all of your imaging equipment; the imaging scope, guide scope, cameras, dovetail bars, scope rings and anything else you want to hang off the mount. You will be much more likely to succeed with grossly over mounted equipment than you will with a mount that is struggling at close to its maximum carrying capacity. I know the feeling well, “If I buy the HEQ5 instead of the NEQ6 I can spend the extra money on a bigger scope..” Bad decision. Buy the big mount and the small scope; if you’re serious about imaging there will always be another scope along later! Managing weight is always a compromise. Finder-guiders are cheap and lightweight but may have too short a focal length for your imaging scope (see below). Losmandy-style dovetail plates and solid tube-rings add weight, but lightweight alternatives may make it hard to avoid flexure (again see below). You will find it helpful to weigh your components or check the specifications of any potential purchases and keep a running tally of the total. Choose the right Guide Scope and Camera In order to have the best chance of guiding successfully, you need to match your guide scope/camera to your imaging scope/camera. Now I know you may have read some received wisdom that when using PHD Guiding you don’t need to worry about matching the guider and imager; that is true but only up to a point. The next tip is to is to match the pixel scales of the guider and imager. By ‘pixel scale’ I mean the angular resolving power of the scope/camera combination in arcseconds**. If you are using an OAG or a self-guiding camera, even though you are guiding and imaging through one scope, it is still worth understanding whether your imaging camera, guide camera and scope work well together or not. (It is unlikely that you will have a problem unless you have a ridiculous difference in pixel sizes between the two, but knowledge is power!) PHD Guiding can track the centroid (centre point) of a guide star to ‘sub pixel accuracy’. Basically it is able to calculate the position of the guide star down to a fraction of a camera pixel. This leads people to the erroneous conclusion that they don’t need to worry about matching pixel scales of guider and imager because PHD can “track to a 10th of a pixel” or even “a 50th of a pixel” (depending on who you ask). In theory that is true, but in practice you are not likely to get PHD guiding reliably to more than one quarter of a camera pixel. So a good rule of thumb is your imaging pixel scale should be no more than four times your guiding pixel scale. You might be able to exceed 4x by some margin, but sticking to less than that will make your life much easier. So how do you calculate your pixel scale? pixel scale in arcseconds per pixel = (camera pixel size in µm / scope focal length in mm ) x 206.3 So I image with a Canon EOS 500D with pixels that are 4.7µm square and a Skywatcher Evostar 80ED and 0.85x Reducer with an effective focal length of 510mm: (4.7µm / 510mm) x 206.3 = 1.9 arcseconds per pixel I guide with a QHY5 with pixels that are 5.2µm square and an Orion ST80 with an effective focal length of 400mm: (5.6µm / 400mm) x 206.3 = 2.67 arcseconds per pixel If you don’t feel like doing the maths, use my Imaging Toolbox to do the hard work for you. The upshot is that I my imaging resolution is about one and a half times my guiding resolution (2.67 / 1.9 = 1.41). That is well within the 4 x rule we established above. Don’t forget, you can use a Barlow lens or a focal reducer to adjust the relative pixel scales of imager and guider. For example, the quality of the image through the guider is not critical so a cheap Barlow can be used cut the number of arcseconds per pixel if needed. Now there is a lot more that could be said about the optimal pixel size of imaging cameras vs different scopes, but that is another topic. The best advice I have read is that your first priority is to have a scope and camera combination that can fit your target in the frame, and to worry about everything else later! Again using the Imaging Toolbox you can try different combinations of scope and camera to see what works. ** One arcsecond is 1/3600th of a degree, which is a pretty small angle. Eliminating Flexure Differential Flexure occurs when the imaging rig and the guiding rig end up pointing in different directions over the course of one exposure. There are two main causes of flexure: - The guiding rig and the imaging rig are not joined together in a mechanically sound way. As the mount moves to track the sky, gravity or cables pull on one part more than the other and they end up pointing in different directions. Usually this is simply a matter of loose mechanical connections between the two scopes allowing them to bend or twist out of alignment. - Parts of one of the rigs move, causing the image to shift. The two most common causes of this are the mirror shifting or flopping in SCTs (and other moving mirror scopes), or a drooping focuser tube which bends under gravity. Technically these are not ‘Differential Flexure’ but the net effects are the same, as are the solutions. The fundamental problem is that PHD will be successfully keeping the guide star in one spot on your guide image, but because the guide scope image is moving relative to the main scope image, the main image ends up trailing. If you are using an SCT or similar scope, an OAG or self-guiding camera is the surest way to address this problem. As the mirror flops under gravity, the guider sees the image shifting in exactly the same way as the imager does and compensates for it. If you are using a piggy-back or side-by-side guide scope, you may find that you get good results when the scope is pointing in one direction, but not in another. This is often a sign of mechanical flexure of some sort, as the effect of gravity causes things to bend more in some orientations than others. The next tip for guide scope users is to sort out your mechanical connections: - The biggest culprit is adjustable three-point guide-scope rings (like a set of giant finder-rings). The ones with plastic screws are an absolute disaster, and even the plastic-tipped metal screw variety can cause problems. Avoid at all costs and use a set of solid scope rings for your guide scope: We've all got a set of three-pointers in the bottom of the junk box having learned the hard way! (You do not have to have the guide scope and image scope perfectly aligned for short focal length exposures of 10 or 20 minutes, and with a decent guide camera you won’t need to hunt around for a guide star.) - If you are using a finder-guider, try to use a pair of solid rings. Avoid three-point finder rings if possible (especially plastic screws), and never use a the rubber o-ring type of finder holder that you get on many cheap scopes! - Check for cable snags or pulls. It is tempting to leave a nice long loop of cable from the cameras to the computer to avoid it snagging on the mount, but the weight of the cables can be enough to cause flexure. The best solution is to run the cables from the cameras up the scope tube to the midpoint of the scope without leaving a big loop, fix them there with Velcro or a tie and then run back to the computer from that point. - After that you will need to look at the connections between mechanical components for signs of flexure. If you can hold the imaging scope in one hand, the guide scope in the other and make them move visibly by applying gentle to moderate force, you may well have an issue! Even if things look solid, it only takes a few arcseconds of flexure to ruin an exposure, and the amount of movement between the scopes needed to cause that is imperceptible to the human eye. Tighten up bolts (but beware of over-tightening and stripping threads), file any contact surfaces flat, add shims, washers, extra bolts, screws and brackets as needed to keep everything rock solid. - Check your focusers for droop. The focus tube will be pulled downwards under gravity and as the scope rotates it can cause the guide image or the main image to shift. Make sure your focuser tensioning screws are properly adjusted; you should be able to point the scope straight up and not have the weight of the camera cause it to slip. Also apply the lock screw as part of the focusing process if you have one. Using it can cause the focus to shift in cheaper models, but it will reduce the tendency to droop or slip, so learn where to set the focus point to allow for this final shift. Ultimately you may need to fit an upgraded focuser if you have a heavy camera. Other Causes of Trailing that are not Guiding-related Camera non-orthogonality causes elongated stars. This means that the camera sensor is not exactly perpendicular to the telescope’s focal plane, so the stars get stretched in the direction of greatest tilt. You can diagnose this problem as follows: - Aim the telescope at a group of bright stars about 40 or 50 degrees above the horizon and take a short exposure of a few seconds, long enough to capture the stars but short enough that you would not get trailing due to poor tracking. Look at the image and see if all the stars are elongated in the same direction. If so, it is likely that you have non-orthogonality. - Now rotate the camera through 90 degrees with respect to the telescope and take a second short image. Figure out which direction is ‘down’ towards the ground in each of your pair of images. If the elongation in both images is in the up/down direction, then you most likely have a problem with the focuser or other element drooping under gravity. - If the direction of elongation changes as you rotate the camera, then you probably have a mechanical problem in the imaging train. Very occasionally the problem can be with the camera sensor not being parallel to the mounting ring on the camera body, but it is more likely that something is cross-threaded or not fully screwed together. I recently had a problem with a retaining ring in a light pollution filter that was not fully screwed in and this caused the camera to about 0.5mm off true. My next tip is to obtain a set of digital callipers. These are invaluable in checking orthogonality of the various elements in the imaging train, as it can be pretty hard to spot small misalignments by eye. Use them to measure the gaps between the same points all the way around the focus tube or other element to ensure that it is the same. As a bonus, you can use them to measure and subsequently set the focus position of your scope at the start of the night. Optical aberrations such as coma can cause elongated stars. This is easy to diagnose as aberrations cause elongation in different directions across the image (typically pointing outwards from the centre towards the corners), whereas guiding issues will cause trailing or elongation in the same direction for all stars in the image. Vibration is a common problem that is easily mistaken for poor guiding. There are two main causes of vibration: - Environmental causes, typically you, dear reader. You need to do your best to isolate your mount from external sources of vibration. A solid tripod or pier, anti-vibration pads, etc. The list of cures for vibration is endless and I’ll leave you to do your research on that one. If your imaging software allows it, program in a pause before the first image is taken. Use that time to walk away from your scope since your size tens are more likely than not to be a source of problems even on a solid concrete pad. - Camera-induced vibration is typically a problem for DSLR imagers. When starting an exposure, the mirror makes a very satisfying ‘clunk’ as it flips up out of the way before the shutter opens. That tends to induce plenty of vibration in the imaging rig. Most astro-DLSR applications have the ability to program a pause between the mirror lock-up and opening the shutter. I recommend setting this pause to at least five or ten seconds to allow vibration to die down. Wind is also a big issue. If you find you are getting erratic guiding or stars that look like they have been drawn with a spirograph (wiggly lines all over the place), it may well be that the wind is causing your scope to wave around like a windsock. Bigger the scopes like Newtonians have more surface area and can suffer from this problem more. Look for a sheltered spot or wait for better weather. Poor Seeing is also a problem. There are techniques that can help with this (see below) but you will find that the quality of your guiding definitely varies according to the seeing conditions. If you get it right, you’ll end up with bigger (but still round) stars on nights of poor seeing, but if you get it wrong you can end up with trailing or wiggly lines as above. ST4 Cable or ASCOM Pulse Guiding? As you may be aware, there are two typical methods of sending guide corrections to the mount. Some cameras may be connected directly to the mount by means of an ST4 cable, so guiding corrections are sent by means of electronic signals to the mount controller board. Alternatively, guide corrections may be sent through software via the mount driver (typically the ASCOM platform and drivers on a Windows PC). Which is ‘better’? The reality is that neither method is intrinsically better than the other. There is no performance advantage in using an ST4 cable over using ASCOM pulse guiding, as the time taken for corrections to reach the mount is minuscule compared to the duration of even a 1 second guiding exposure. If you are using an auto guider which calculates its own guiding corrections on the camera, then using ST4 may make things simpler as you can do away with one set of drivers on the laptop (or not use a laptop at all if capturing images directly on a DSLR memory card). We are talking about PHD guiding here though, so I’ll assume that isn't the case. - If you wish to use an ST4 cable with PHD guiding, you should select ‘On Camera’ from the PHD ‘Mount’ menu to tell it to send guide commands via the camera’s ST4 port. - If you wish to use ASCOM pulse guiding you would select ‘ASCOM’ from the mount menu, and choose the appropriate mount from the dialog when you press the ‘connect to mount’ icon on the PHD tool bar. - For non-ASCOM mounts supported by PHD, you’d choose the appropriate mount from the menu instead. To PEC or not to PEC? Periodic Error Correction (PEC) is a feature of some mounts and/or their drivers. All mounts will suffer from Periodic Errors in tracking in the RA axis, which relate to the rotation of the RA gears (gear periods, hence the name). As the gears rotate, machining imperfections in the gears cause the tracking to drift East and West of the correct position in a repeating cycle. The PE of a high end mount might be a few arcseconds, but on a low end mount (sub £2,000) a PE of 10 arcseconds is considered ‘good’, and figures much higher than that are not uncommon. PEC records those errors by monitoring guiding corrections for at least one full cycle of RA worm gear. Subsequently the mount (or driver) plays back those errors to correct the tracking before it drifts off target. When used properly, PEC should be superior to guiding alone since it prevents most of the tracking errors before they happen, not after they are detected. Whether you should use both PEC and guiding together is an ecumenical question! If used properly, then PEC should give superior performance to guiding alone, but I am definitely in the camp that thinks it is rather a lot for a beginner to take in conjunction with learning the ropes of guiding. If you are using an HEQ5, NEQ6 or related mount with the EQMOD drivers on your laptop and you also want to use EQMOD’s PEC features, you should definitely use ASCOM pulse guiding. The drivers have been written to properly combine the PEC corrections with pulse guide commands from PHD (or any other software that produces pulse guide commands). This avoids conflicts between PEC and PHD which could otherwise over or under-correct guide errors, whereas using an ST4 cable with EQMOD PEC may result in such problems. (Thanks to Chris Shillito, EQMOD guru and all-round good guy, for his many patient posts on this subject which I am paraphrasing here). Proper Preparation makes for Pixel Perfect Performance My next tip is to do as much testing as possible during the daytime. It is much easier to solve problems when you are warm, indoors and have plenty of time. Trying to solve problems in the dark, cold and when you feel like you are wasting precious imaging time is a recipe for silly mistakes. - Do a dry run of your entire set-up and imaging routine. Check you know where all the cables go and that they are not loose or prone to disconnection. Check that all the software can see the cameras, mount, etc. Ensure that all drivers are installed and properly configured. Last of all do a complete ‘systems check’ to ensure that everything works together. I have had many issues where individual components work fine, but fail when asked to work together, e.g. EQMOD works on its own, but not with PHD connected, or APT works but not with EQMOD, etc. - Check your guiding rig can achieve focus. You may find that you don’t have sufficient back-focus on your guide scope or finder and you need to add an extension tube. Focus on a distant object in daylight to verify this. - Note the focus position of your guide scope and your imaging scope. You can get close during the day but you will need to refine this by focusing on a star. Again I have wasted many hours struggling to get cameras focused; unlike eyepieces it can be incredibly hard to tell where the focus point is until you are almost there, and how do you even know if you have a star in frame if you are way out of focus? - Once you do have good focus on both scopes, measure the length of focus tube that is out of the focuser body. You could mark it with a pen (not good for resale value), or make a focus measure with a strip of metal or stiff plastic that just fits between the camera and the focuser body when you are in focus. You can sit it on the focuser tube and instantly get close to the focus point with no effort. - Review the software settings described in the sections below until you are familiar with them and have a reasonable idea of what they do. It can be very confusing at the outset with so many knobs and dials to fiddle with, so try to learn as much as you can during the day or when it is cloudy. - Test that PHD can connect to your camera and mount, and that it can send guide commands which are acted upon: Camera: Firstly connect to the camera by pressing the ‘camera’ icon on the left of the PHD tool bar. A dialog box will pop up and give you a choice of camera types to choose from. You’ll have to read the manual (or search the forums) for advice on which option is the right one for your camera as they do vary, and debugging camera drivers can take a fair bit of time when you first start out! It is worth knowing that some cameras allow you to adjust the camera gain (brightness) from within PHD using the ‘Cam Dialog’ button at the right of the PHD tool bar, but for other cameras you can only adjust the settings at the point where you first connect to it. If so, you will need to use the camera button to disconnect/reconnect the camera each time you want to make an adjustment. You will not see anything on screen when you connect to the camera. The next thing you need to do is press the ‘Loop’ button, the blue circular arrow third along on the tool bar. This will start taking repeated exposures (by default 1 second exposures). You can test whether the camera is working by covering and uncovering the scope (the PHD display should go black when covered and brighten up when uncovered). If you see nothing, then it is time to check your drivers, adjust dialog settings to increase/decrease gain, etc. Mount: Next you should test your mount connection. Make sure you select the appropriate mount from the PHD ‘Mount’ menu and then click the ‘Telescope’ icon second from left on the tool bar. You may be presented with a dialog to choose the mount driver depending on the model; again check the forum for advice on your specific mount. Test Guiding: The final check (for now) is to ensure that your guide commands are making it through to the mount. Once you have successfully connected to the mount, you should set it to sidereal tracking rate (using EQMOD, the mount handset or whatever method is appropriate to your mount). Listen carefully to the mount and you will probably be able to hear the mount motors driving the mount as it tracks (it may be a very quiet singing/whistling sound for example). You won’t see the mount visibly moving though, as it will take 24 hours to rotate 360 degrees in RA. Next go to the PHD ‘Tools’ menu and select ‘Manual Guide’. You will see four buttons to send short guide commands in North, South, East and West Directions. Start by repeatedly clicking the ‘West’ button and listening carefully to the tracking mount. You should hear the motor sounds change slightly as you click, which indicates that the guide command was received and acted upon. Next try the ‘East’ button. In this case you may hear the motor sounds change or more likely stop momentarily. Finally try the ‘North’ and ‘South’ buttons and you should hear the Dec motor starting up and stopping. Bear in mind these sound are quite subtle and you may not be able to detect them. If you can point the main scope at a distant object and use a high-power eyepiece, you can visually check whether the mount is moving when you click the manual guide buttons. If not, you will have to wait until you can get it out under the stars, but it is better for your sanity if you can confirm that PHD is in control of your mount during the hours of daylight. Aligning the Mount for Imaging Now when I said Polar Alignment wasn't that important, I didn't mean you can forget about it entirely. You should certainly perform a reasonable polar alignment using the polar scope and the appropriate procedure for your mount for two main reasons: 1. Whilst some new mounts and/or software can get your scope’s GOTO aligned however bad your polar alignment, most mounts still rely on a reasonable polar alignment to get the process started. If you can’t get your scope’s alignment routine going, you aren't going to be imaging very much. 2. Both equatorial mounts and fork mounts on wedges rely on polar alignment to track the sky properly. If you have a poor polar alignment, your exposures may well suffer from field rotation. Basically the stars will not stay as pinpoints but will form short curved arcs instead. This is more likely the longer the exposure length and/or the longer the focal length of your imaging scope. With a short focal length scope for (say) ten minute exposures, a polar alignment done with just the polar scope will be fine. If you’re imaging with a long focal length scope and going for hour-long exposures, then you may well need to drift align to avoid field rotation. It is worth noting that using a guide scope that is not aligned with the imaging scope can also cause field rotation, but the same caveats apply, i.e. for a short focal length/short exposure don’t worry about it too much. Before we go any further, there are some important points to understand about how the mount’s mechanics work: - All mounts track by means of motors which drive a system of gears; one motor and set of gears for the RA axis to track in the East-West direction, and one motor and set of gears for the Dec axis to track in the North-South direction. In a mass-produced mount, those gears are manufactured to a price; they are not hand-crafted things of beauty and they will have various imperfections that cause tracking errors. - In even the most perfectly made set of gears, there is an amount of ‘backlash’. Put simply, there has to be a gap between the gears; if they fitted together perfectly then the gears would be unable to turn at all. That gap causes problems when the gears reverse direction, since the gear has to turn a certain amount to stop pressing on one side of the teeth and start pressing on the other, so there is a delay before the gears start moving the opposite way. A high-end set of gears will have a small amount of backlash, but guess what? We’re not dealing with a high-end set of gears and there can be a lot of backlash in a typical low-end mount, especially if it wasn't well adjusted at the factory. - Backlash should not be a problem for tracking in RA. When tracking, the mount should always be driving the scope from East to West and will not reverse. There may be a small amount of backlash at the start of tracking if the mount’s last GOTO was from West to East, but this is quickly taken up. PHD guiding will speed up the RA motor if it needs to move West to correct a guide error. It will stop the RA motor if it needs to correct to the East, and wait for the sky to ‘catch up’. In other words once tracking has started, the RA gears will never reverse and enter into backlash. - The same cannot be said of the Dec axis. In this case, if PHD needs to guide North, it drives the Dec motor North, and if it needs to guide South it drives the motor the opposite way. If your set-up constantly requires PHD to keep guiding in opposite directions in Dec, the gears will spend a lot of time in backlash, which delays the guiding corrections from taking effect and may cause PHD to over or under-correct the error. The ideal situation is that all Dec guiding corrections be made in one direction only (North or South, it matters not) so that the gears stay out of backlash. PHD will do its best to make that happen (unless you tell it not to), but there are things you can do to assist it. The next tip is not to sweat too much over drift alignment. If you have been imaging using an unguided mount, you may well have put a lot of effort in to drift aligning the mount to maximise exposure time. Contrary to your expectations, when guiding a small amount of polar misalignment is not a major problem when guiding a short focal-length imaging scope.. If your target is drifting slightly in declination (either North or South) that will ensure that ensure that guide corrections are made in one direction only, thus keeping the Dec drive out of backlash. All things in moderation though: - You don’t want such a misalignment as to cause visible field rotation during your exposures. - Nor do you want so much misalignment that you cause PHD’s calibration routine to fail (see below). If you have severe drift in Dec, PHD may interpret the drift as resulting from its calibration commands and will end up under-correcting when guiding in Dec. As stated previously, I find that a polar scope alignment works really well for my short-focal length imaging, but the longer your focal length, the more critical a good Polar Alignment becomes, and thus part of the reason why imaging at long focal lengths is hard. If you do have perfect polar alignment (i.e. you are drifting so little it produces no visible effect on the image during one exposure), you can switch off Dec guiding altogether. Click on the ‘Brain’ icon on the PHD tool bar and set ‘Dec Guide Mode’ to ‘Off’. This might be the case if you have a permanent observatory with a pier and a rock-solid mount adjustment. For the rest of us, it is probably quicker to leave ‘Dec Guide Mode’ on ‘Auto’. and let PHD work out what to do for the best. Balancing the Mount The next tip, if using an equatorial mount, is to think about Balancing it, or should I say not balancing it! The mount manual will probably explain that it is important to check the balance of the mount, so that the RA and Dec axes will stay in a horizontal position when the clutches are unlocked. It is certainly true that you do not want a massive imbalance in either axis, especially if using heavy equipment, as this will put a lot of strain on the gears and motors and may lead to premature wear. That said, obtain perfect balance is actually bad for tracking and guiding performance on low-end mounts: - The usual advice is that the mount should be “East-side heavy”, so that it is working to lift whatever is on the east side of the mount. So if the scope is on the East side of the mount (pointing West of the meridian) then you should move the counterweights up the counterweight shaft slightly higher than the perfect balance point. Conversely, when the counterweights are on the East side of the mount (scope pointing East of the meridian), move them down the shaft below the perfect balance point. You are aiming to have the RA worm (one of the gears) drive the main RA worm gear. By keeping the RA axis imbalanced to the East, you force the gears to stay in contact with each other (‘driven’ imbalance). This tends to smooth out any sudden movements more than the opposite (‘resistive’) imbalance. In the resistive set-up, the worm gear may slip or jolt suddenly due to uneven machining. This can also happen with driven imbalance, but most people report better results with driven imbalance than resistive imbalance. My personal experience with my NEQ6 is that so long as I have some imbalance in RA, it doesn't particularly matter which side is heavy. In fact when I am within 30 minutes of having to do a meridian flip, I will often pre-emptively do a ‘forced flip’ between exposures (so I can get back to a frosty beverage of my choice and watching the TV on the nice warm sofa). The scope ends up on the ‘wrong’ side of the mount (East Side pointing East) with the counterweights higher than the scope until it tracks through the meridian. I’d expect at least one bad exposure as the weights drop through horizontal and the gears switch from one face to the other, but it never happens. Again I suspect that using a short focal length imaging scope gives me a lot of room for manoeuvre! - The same sorts of consideration apply to the Dec worm and worm gear (unless you are not guiding in Dec of course). You need to imbalance the Dec axis by moving the scope forwards/backwards (or adding weights) depending on which direction you are pointing relative to the zenith so that you achieve driven resistance. If you have southward drift: - If the scope is pointing South of the zenith, imbalance the scope so that the North (lower) end is heavy. - If pointing North of the Zenith, again imbalance so that the North (higher) end is heavy. If your polar alignment is causing a gradual northward drift instead, then you reverse the imbalance: - Pointing South of zenith, South/higher end heavy. - Pointing North of zenith, South/lower end heavy. PHD Basic Settings We looked at a few of the basic PHD settings during testing above, so hopefully you already know how to get your camera and mount connected to PHD ready to start guiding. Next we will look at a few of the more important settings. Exposure Length In the middle of the PHD tool bar is the ‘Exposure’ drop-down, which allows you to choose the length of the guiding exposures in seconds. Setting the exposure length is a trade-off between several factors: - You need a long enough exposure to produce a measurable guide star. If your exposure length is too short (and/or your camera gain too low), you will either get no stars or stars that are too faint to use reliably. If you find you are able to lock on to a star and calibrate, but then get frequent ‘Star Lost’ errors flashing up, it may be that your chosen star is too faint. Increase the exposure length (and/or gain). (Bear in mind that cloud can cause the same problem as it drifts across and dims the guide star from time to time, so check the skies, especially for high, thin cloud which can be hard to spot. Also check your guide-scope for dewing which has much the same effect.) - You need a short enough exposure not to saturate the guide star. If your exposure length is too long (and/or your camera gain is too high) you may get a ‘Star Saturated’ error from PHD. This means that one or more of the star’s pixels has reached maximum brightness and PHD cannot calculate the star’s centroid accurately. Reduce the exposure time and/or reduce the gain. - You need an exposure length that is short enough that PHD can detect and correct guiding errors before they become visible on your main image. In an ideal world we’d take guide exposures as frequently as possible, but in practice there is a minimum length of exposure dictated by the need to pick up a guide star (see above). Furthermore it can be advantageous to have a longer exposure to reduce the effect of seeing. Really short exposures can end up with PHD “chasing the seeing” and poor guiding, whereas a slightly longer exposure averages out the seeing and gives a better estimate of the guide star’s centroid. - When you have selected a guide star, the star’s ‘Signal to Noise Ratio’ is displayed at the bottom left of the PHD window on the status bar. There is no hard and fast rule as to what this number should be. Generally speaking a higher number is always better, provided you are not getting ‘Star Saturated’ errors from PHD. Use the SN number to tweak your exposure length, camera gain and focus until you get a reliable lock with no ‘Star Lost’ or ‘Star Saturated’ errors. If you are really struggling to get an acceptable SN number with your camera, you can go in to the ‘Brain’ icon on the tool bar and change the ‘Noise Reduction’ setting from ‘none’ to ‘2x2’ or ‘3x3’. This increases SN by ‘binning’ pixels in software at the cost of reduced guiding accuracy. If trying the 2x2 setting, multiply the camera pixel size by 2 (or by 3 if using 3x3 setting) and calculate the guider pixel scale using the equation we discussed above. If you are still within the 4x pixel scale rule of thumb, you will probably be OK. - The best advice I can give you for exposure length is to start with a two or three second exposure and work from there by reference to the guiding graph, which we’ll look at below. Over a few sessions you’ll get the hang of the right exposure length for your equipment. - Bear in mind my earlier comments that if you are pushing the envelope and imaging at a long focal length, you may need a more sensitive guide camera, a longer focal length and/or faster f-ratio guide scope (hard to do both), to use PEC in addition to guiding or simply a higher quality mount. The next tip is that it might help defocus the guide scope slightly. If you are having problems with saturated stars, or you are exceeding the 4x pixel scale rule, this may help. Defocusing will spread the light of the star over more camera pixels which can prevent saturation, and also makes it easier for PHD to detect the centroid of the guide star more accurately. Don't go mad with defocusing or PHD won't be able to lock onto the star and you may start getting ‘Star Lost’ errors if your SN figure drops too much due to de-focusing. In all cases your guide star still needs to have a brighter central peak and not turn into a hollow doughnut, but a bit of defocus on the guide scope may help where you have SN to spare. You can use the ‘Star Profile’ option on the ‘Tools’ menu to check the profile of your guide star once selected. It should have a peak in the middle like a mountain. If it is flat on top you have a saturated star, and if there is a dip you need to focus more. Brightness Slider Next to the exposure drop-down is a brightness slider. It is essential to realise that this slider only increases or decreases the brightness of the guide image display. It has absolutely no effect on the camera settings or the actual brightness of the guide image. You can use the slider to make it easier to see stars on screen, but if the stars are too faint (or bright) for guiding you have to adjust the camera gain or exposure length, as this slider has no effect on guiding performance, Take Dark Towards the right hand side of the tool bar is the ‘Take Dark’ button. You should definitely use this. Click the button when ready to start guiding. PHD will instruct you to cover the guide scope and then take a series of dark frames. Finally it will remind you to uncover the guide scope again (been there, bought the t-shirt!) Failing to take a dark can cause two problems: - Firstly you may end up selecting a hot pixel as your guide star. Normally PHD will spot this and complain, but you may waste a lot of time trying to calibrate on it if it doesn't (or even guide on it if retaining an existing calibration). The guiding graph looks great since the hot pixel stays dead centre of the lock box, but the final images do not! - Secondly as you guide, a hot pixel may be close to the guide star, and PHD may intermittently include the hot pixel as part of the star image causing the centroid position to jump around erroneously. Bear in mind that whenever you change exposure length or camera settings, you should re-take your dark using this button. Getting ready to Guide So now you are ready to go. You have found your target for the night, you have framed it nicely and focused your imaging camera and set the basic PHD guiding parameters above. The next steps are as follows: - Click the ‘Loop’ button to start taking guide exposures. Hopefully you will see a choice of guide stars in the PHD screen. If you don’t go back a few steps and adjust the exposure/camera gain and try again (re-taking your dark if needed). - Click on the brightest star but avoid using a star that is close to the edge of the image, as it may drift out of view over the course of the imaging session (especially if you are dithering your images). Check that PHD is not complaining about the star being saturated, and ensure that PHD has found the star (it should draw a green box around it if it is happy). - Avoid picking a star that is close to another star, and also avoid using any known double stars. In both cases you may end up with erroneous/fluctuating centroid calculations and spurious guide commands. Calibration - Next click on the ‘PHD’ button and PHD will start the calibration process. It will attempt to move the star some distance East and West in RA, and then North and South in Dec in order to figure out which guide commands move in which orientations and also how long guide pulses need to be.. A pair of lines will be drawn in a cross indicating the initial position of the guide star, and you will see the status bar indicating which guiding commands are being sent. All being well you will see the star and the green box gradually drift along one of the lines, stop and drift back again, and then do the same along the other line. This process can take several minutes to complete successfully so be patient. A good calibration will usually require somewhere between seven and forty steps in each direction. If the calibration completes in less than seven steps in any direction, you are unlikely to get good guiding performance and you should change the calibration step size (see below). If the calibration takes more than forty steps in any given direction it will still work, but again you may want to change the calibration step size to save time. My experience is that a good calibration takes about 15-20 steps and between five and ten minutes to complete. If the calibration fails with PHD complaining that the star didn't move enough, then you have one of two problems. Either the calibration step size is too small (see below), or your guide commands on one or both axes are not being acted upon. We talked about using the ‘Manual Guiding’ option on the ‘Tools’ menu to verify that PHD can control the mount, so if you haven’t done so already, put a high-powered eyepiece in your imaging scope, centre a star and then use those controls to make sure the scope moves in all four directions when commanded. The final thing to be aware of is that you should recalibrate PHD whenever you slew to a new imaging target (unless it is within a few degrees of your original target). You do this by clicking the ‘Brain’ button on the tool bar and ticking the ‘force calibration’ button. You will not be able to successfully guide if you try to keep the same calibration in different parts of the sky. Similarly if you perform a meridian flip on an equatorial mount, you should probably re-calibrate. There is an option on the ‘Brain’ dialog to reverse the existing calibration after a flip, but my experience is that it is better to spend five or ten minutes recalibrating rather than spending ten minutes exposing only to discover you have to recalibrate anyway! Calibration Step Size and Guiding Rate If you are have a good guide star (good SN figure, not saturated), and PHD is definitely able to command the mount but calibration fails, then it is a fair bet that the Calibration Step Size number needs to be adjusted. Click on the ‘Brain’ icon on the tool bar to bring up the advanced PHD settings. The “Calibration Step Size’ determine the length of the calibration guide pulses. The default setting is 500ms (half a second). This may or may not be the right amount: - The bigger the pixel scale of your guiding rig, the longer the step size should be. I use 2,000 to 2,500ms for my 400mm/5.6µm guide scope at 2.67 arc-second per pixel. If your pixel scale is a bigger number, increase the step size, if smaller decrease it. - The closer you are to the celestial pole, the longer the step size should be. Typically I use 2,000ms near the celestial equator and increase that to 2,500ms as I approach the pole. The appropriate range will vary according to the pixel scale of your guiding rig. - Your mount, or mount driver may allow you to set a custom guiding rate. The best starting point is to set your guiding rate to 1x, which means that when guiding East the mount will stop completely, and when guiding West it will move at 2x sidereal rate. Many mounts offer 0.5x guiding rates (and others), which are helpful when hand guiding, but probably not that much use when using PHD. keep it simple and use the 1x guide rate. The next tip is that you should experiment with the calibration step size and keep notes of what works for each declination. Provided you are calibrating in more than seven steps you should be OK, but if you are exceeding 40 steps you can almost certainly save time by increasing step size. I aim for 10-20 steps at most. Guiding (at Long Last!) Once PHD completes calibration, it will immediately start guiding. The pair of lines will turn green and guide commands will be sent. Time to start imaging at last. I know it has taken a long time to read to this point, but in reality and with a bit of practice, the time from finishing centring and focussing my imaging target in the main scope to having PHD guiding merrily away takes me seven minutes on average, and for about 6 minutes and 30 seconds of that time, PHD is calibrating without any input from me! As far as guiding goes, the next thing you need to do is monitor the PHD status bar for a minute or two to make sure you are not getting ‘Star Lost’ or ‘Star Saturated’ errors. The occasional ‘Star Lost’ error is nothing to fret about usually, but if they are flashing up repeatedly you should do some troubleshooting (check exposure and gain as described above, look out for high cloud and dewing on the guide-scope). Interpreting the PHD Graph The most useful tool for checking your guiding performance in the field is the guiding graph. Go to the ‘Tools’ menu and select ‘Enable Graph’. What you will see is a graph showing your guiding performance in RA (the blue line) and in Dec (the Red line). The name of the game is to try to keep the two lines as close as possible to the centre line running from left to right across the chart. The horizontal scale button (‘100’ above) allows you to zoom in and out by reference to guiding cycles. By default 100 guiding cycles are shown across the chart, this isn't a fixed time scale as such and the longer your individual guide exposures, the longer those 100 cycles will take. You can click the scale button to zoom out and see more cycles, but to be honest the default 100 cycles is most useful for diagnosing guider problems. The vertical scale button (RA/Dec) allows you to switch between RA/Dec corrections and x/y pixel corrections. Again the first mode is most useful since you want to see what is going on with your RA guiding and Dec guiding separately, whereas the x/y mode isn't (necessarily) much help in that regard. Again the vertical scale is not too helpful at first sight. Each dotted line corresponds to one pixel of error on the guide camera. Since you have calculated the pixel scale of your guide camera already, you can multiply it by the number of divisions to find your maximum guide error. In the graph above I was using my ST80 and QHY5, and the blue RA line averages out at about 0.2 pixels above/below the line, making for an error of: 2.67 arcseconds per pixel x 0.2 divisions = 0.53 arcseconds. This is what we call the “Root Mean Square” or RMS error, which basically means we square the all the errors (positive stay positive, negative x negative becomes positive), add them together, average the total and take the square root. If we didn't calculate the RMS then the negative errors (below the line) would cancel out the positive errors (above the line) and our average error would be close to zero, which clearly it is not! Helpfully PHD calculates the RMS error for whatever you can see on the current graph scale and puts it on the bottom left of the graph below the buttons. It only does this for the RA error however (the blue line) as it is assume you will not be making major Dec corrections at all (not always true though!) The other figure just below RMS is the ‘OSC Index’, i.e. the oscillation index. Again this is only calculated for the RA axis. The OSC index is the probability that guiding will change direction at the next step (i.e. the blue line will cross the centre of the graph) A mount with no Periodic Error would have a figure of 0.5, i.e. equally likely to have to correct in either direction, but a figure between 0.25 and 0.4 for a real mount is generally considered okay but there isn't a hard and fast rule about the OSC index: - If you have a small RMS figure and a large OSC index you should be okay. The mount is constantly flipping between guide directions but only by a small amount. - If you have a large RMS figure and a large OSC index, that would tend to suggest the poor guiding is due to lack of stability in the set-up, and that could be down to mechanical/balance problems, wrong exposure/gain on the camera creating a noisy guide star, incorrect guiding parameters or just really bad seeing conditions. Unhelpfully in my example, the OSC index is greater than 0.5, which suggests the mount is correcting more in RA in one direction than the other over time. I'm man enough to admit I don’t know what that means! What I do know is that I got really good imaging results from that session so clearly it wasn't a problem to worry about. Common Issues from the Graph - First of all, please bear in mind that you can have a pretty ugly looking guiding graph that produces little or no visible effect on the actual image. The opposite is also true of course! You need to convert the pixel lines on the vertical scale and/or the RMS error to arcseconds of error by performing the guider pixel scale multiplication described above. Now compare that to the pixel scale of your imaging rig. You may find that what looks like a major guiding issue is actually less than a pixel or two of error on your final image. For example, looking at the RA error in the graph above: 0.2 RMS pixels error x 2.67 arcseconds per pixel = 0.53 arcseconds of error on the guider image 0.53 arcseconds of error / 1.9 arcseconds per pixel imager scale = 0.28 pixel RMS error on final image Looking at my graph, I can see that the RA error is roughly evenly distributed above and below the line so I should double the RMS error, meaning my stars are perhaps half a pixel wider than they should be in RA. The Dec error looks pretty much the same. Sounds pretty good to me, and indeed it looks good on the final result. (If the guide error was predominantly above the line, or predominantly below the line, we could use the smaller 0.28 pixel RMS value instead). - If one or other of the RA/Dec lines is shooting off the graph it may mean that corrections in that axis are not being sent to the mount or are not being responded to. Again perform the manual guiding checks to ensure everything is working as you would expect. Also check that you haven’t turned off Dec guiding under the ‘Brain’ button. If everything checks out, ensure your clutches are tight on the mount and look for other signs of flexure or equipment flapping about. (if you are using dithering, it is normal to have the RA and/or Dec lines shoot away from the centre line whilst dithering is in progress, and then drop back to the centre line as dithering finishes and guiding settles. It does tend to make me jump off the sofa when I see it happening on my remote monitoring screen though!) Tweaking Guiding Parameters The next tip is that your results may well vary according to the Alt and Az of the target. I consistently get better results on higher targets nearer to the meridian. Targets lower in the east produce rougher guide graphs. Whether that is due to poor seeing due to more atmosphere in the way of the guide star, something mechanical or perhaps needing to tweak the guiding parameters I know not. If your guiding graph is zig-zagging all over the place and you are getting many arcseconds of error, and assuming you have checked all the basics above, then you may need to tweak some of the guiding parameters. Helpfully the main parameters that you may need to change can be adjusted using the controls directly below the guiding graph: - RA Aggressiveness: How much of the calculated RA correction to apply. Start with the default figure of 100%, as hopefully PHD knows what it is doing. If you find that guiding in RA (blue line) is constantly overshooting the mark and then rapidly zig-zagging back the other way, try reducing this to a lower figure, perhaps 70-80%. If you think your mount has sloppy gears, maybe try going to 110 or 120% to see if you can compensate. - RA Hysteresis: How much of the previous RA guiding trend to take into account. Good guiding is smooth and doesn't respond to rapid changes in guide direction (usually caused by seeing or poor SN from the guide star). If you think that guiding is too jerky with sudden rapid corrections, increase this number, or decrease it to make guiding more responsive. Aggressiveness and Hysteresis go hand in hand and you should normally reduce or increase them together in small increments until you get best results. - Min Motion: The smallest guide error that should result in a correction being made. This is in pixels and applies to both the RA and Dec axes. So if I set min motion to 0.1 pixels, then PHD would not try to correct any errors until they were more than that value, and for my guider scale of 2.67 arcseconds per pixel, that means PHD would not try to correct any errors less than about a quarter of an arcsecond in size. Again this is useful for smoothing out jerky guiding if your mount is poor or you don’t have a good guider set-up. - Max RA Duration: This sets the maximum single guiding correction that PHD will send in a single cycle (in this case 1,000ms = 1 second guide pulse). Generally you shouldn’t make this value too large (maybe less than half a second), since PHD will issue another correction if it needs to, but if the first correction is too large and overshoots you’re already in trouble. (In this case, the rest of the guiding is working well and PHD never gets anywhere near the perhaps excessive 1 second maximum I have set, but your mileage will vary!) - Max Dec Duration: This is the same as above. The default setting is smaller than the default for RA out of the box, and I've never needed to change it. To be honest I think that is the final tip: If it ain’t broke, don’t fix it! It can be very tempting to dive in and start fiddling with the advanced parameters in PHD in the hope of finding a magic formula for pixel perfect guiding. In reality 90% of the guiding problems are external to PHD guiding. Only when you have investigated and fully understood all those externalities will you be able to make an informed decision as to what to tweak in PHD itself. There are many other resources on-line covering advanced PHD fettling, and plenty of people on the forum willing to offer you customised advice and assistance, so please don’t hesitate to ask for help. You’ll probably find their advice more useful if you have done a bit of homework first.
  8. 84 points
    Introduction If someone were to ask what a galaxy is, the simplest answer would be to say a group of thousands of millions of stars, lots of planets, dust, gas and dark matter rotating within the emptiness of space. If they wanted a little more detail, you could point out that some galaxies are so small they contain no more than 10 million stars or so, while others are so big they could have over a billion stars, that is, a million times a million. 1 followed by 12 zeros. You could say that there are an estimated 200,000 million galaxies in the visible universe and the average distance between them is 15 to 20 million light years. Unable to imagine such vastness, it comes as no surprise that even Andromeda, the closest galaxy to us at about 2 million light years, appears on the darkest, clearest nights little more than a subtle misty blur on the edge of visibility. Knowing that this will be the oldest light you will ever see without the aid of a telescope, cranking open the aperture will still be a night of listening to faint whispers and delicate murmurs as you hunt out galaxies. The world of deep space is a world of almost silence, of muted sounds where nothing breathes and everything is transfixed. The Milky Way Galaxy Before venturing out and exploring, it makes sense to appreciate our own surroundings. That way, we have something to compare our own world to. If home is a place on the planet Earth and the Solar system is our neighbourhood, then on this cosmic scale the Milky Way Galaxy can be considered our country, a single island in a world of hundreds of thousands of millions more. Our cosmic island is around 13,500 million years old and may contain over 400,000 million stars whose average distance is about five light years apart. These stars are spread across a disc about 100,000 light years across and 10,000 light years deep increasing to around 30,000 light years at the Galaxy’s nucleus. An edge on view of the Milky Way would look like two fried eggs stacked back to back. At the centre of the Milky Way is a nucleus containing a bulge of stars while surrounding the entire disc is a spherical halo of older stars and globular clusters extending to a diameter of about 130,000 light-years and containing some of the most ancient stars in the Galaxy. There is also a vast outer spherical region made up of hot, ionized gas which could be as much as 600,000 light years in diameter. Even though there are thousands of millions of stars and each individual star may have a handful of planets, several dozen moons and tens of thousands of asteroids, all this would still only make up a tiny fraction of the Galaxy’s total mass. The Milky Way, along with all the other galaxies, is also in the grip of something mysterious called dark matter. No one knows much about dark matter other than it does not seem to be made of the atoms that make up you and me, or the stars and planets but it outweighs the mass of everything we can detect many times over. There are over 150 globular clusters in the Milky Way. These objects belong to the Galactic Halo and are compact groups of about a million stars moving together around the Galaxy. Globulars are among the oldest objects in the universe and no doubt there are many more to be found but we cannot see them because of the bright band of light reaching across the sky between us and them which rather confusingly is also called the Milky Way. The Sun is about two-thirds of the way out from the centre of the Milky Way, around 27,000 light years toward the edge of the visible disc and perhaps about 22 light years above the centre of the Galaxy’s plane. Like all other stars in the Galaxy, the Sun orbits the galactic centre at about 900,000 km/h and takes about 250 million years to complete one circuit. On that reckoning the Sun and the entire Solar system it carries about with it is about 18 galactic years old while the Sun has barely covered a thousandth of its present circuit in the entire history of Homo sapiens. If we were to fly over the Milky Way, we would see a central bar crossing over the bulge composed mainly of stars and about 30 light years long. From here four tightly wound arms are spiraling from the centre. It is for this reason that the Milky Way is known as a Barred Spiral galaxy. The arms contain mainly hot, young stars which are typically bright and big. Because the more massive a star is, the more intensely it must burn its fuel to hold itself up against the pull of gravity, the more quickly it runs through its fuel and the shorter lived is the star. Such stars may live as little as 10 million years and as such, spiral arms are the sites of rich star formation and death. The Sun is a smaller, mellower star which although forming in one of the spiral arms does not burn nearly so brightly and will outlive many of those hotter stars by a thousand million years. At present the Sun belongs to a large concentration of stars located in the Orion or Local Arm, which is a kind of star bridge between the two major arms of Sagittarius and Perseus. The Orion Arm contains about 25 Messier Objects the majority being open clusters with a small handful of planetary nebulae such as M 27, M 57 and M 97. Stars such as the Sun which form in the arms and disc of the Milky Way are called Population I stars. These contain the recycled material from previous generations of stars which died long ago and so have a greater abundance of elements heavier than helium, including the elements which make up planets and all known life. Older stars are found further out either in the galactic halo or the bulge at the centre of the Milky Way. These are known as Population II stars and their ages range from 10,000 to 13,000 million years old. They tend to be redder than Popuation I stars and less rich in elements heavier than helium. Old star clusters are called globular clusters and because they swarm around the Galactic centre like bees around a hive, they have been used to locate the centre of the Milky Way. If all the stars are circling the galactic centre at colosal speeds and those stars nearer the centre are rotating more rapidly than the stars in the outer regions and thus ceaselessly changing their positions relative to one another, how does the spiral pattern remain? There might seem an easy solution. Stars orbit the Galaxy and the faster stars nearer the galactic centre twist around the nucleus faster than the more distant stars which overtime produces the Milky Way’s spiral shape. The problem is we know that if the idea were correct the spiral would become tightly wound and smear out within 1,000 million years or so. Spirals persist because they appear to be riding a kind of shock wave or sonic boom called a density wave. These waves move through the galactic disc, just as sound waves might move through the air or ocean waves pass through water, compressing and slowing down different parts of the disc at different times. The spiral arms we observe are defined by the denser clouds of interstellar gas and stars the density waves have created and so in a way, spirals are not great masses of stars being transported from place to place, but patterns moving through the Galaxy. The younger stars found in the spirals are the visible feature of the shock waves travelling around the Galaxy. Clouds of gas and dust are also being squeezed as the density waves go on their way. Some of these clouds get compressed sufficiently to trigger star formation. This process begins in large clouds of dust and gas thousands of light years across and containing the material to build millions of stars like the Sun. Within these gigantic cloud complexes are significantly smaller, tighter knots of clouds whose collapse was probably caused by the impact of density waves and the turbulence from the explosions of super massive stars known as supernovae. With the pull of gravity, the gradual knotting of these denser clouds leads to the formation of a star bearing core which gains mass as its gravity pulls in material from the surrounding area. The mass of the star is dependent on the quantity of material nearby and once the star begins to shine, the radiation from it blows away the rest of the cloud. By the aid of density waves and supernovae, star formation and star death becomes a self-sustaining process within the vicinity of the spiral arms. The balance between interstellar material being converted into new stars and the amount of material thrown back into space by dying stars maintains the Galaxy’s spiral shape and enables the process of star birth, life and death to continue for billions of years. Most newly born stars are part of binary or triple solar systems; many will form open clusters while solitary stars like the Sun are rarer. Whether the Sun was part of a more complex star system is open to debate which perhaps is ultimately premised on the anthropic principle. If our Sun were part of a more complex star system or cluster, we would probably not be here to observe it, for either life would never have developed or evolution would have taken a vastly different course. Astronomers estimate that there are over 100 million black holes in the Milky Way Galaxy, the stellar remnants of stars whose mass was at least twenty times that of the Sun. In the life of a star there is a cosmic game of tug of war between gravity pulling in and pressure pushing out. Nuclear reactions in the star produce sufficient pressure to balance the force of gravity and depending on its initial mass the star will remain stable for millions, if not thousands of millions of years. When a star nears the end of its life and starts to run out of fuel, gravity takes over and the material in the core is compressed even further. The more massive the star’s core, greater is the force of gravity that compresses it. For smaller stars, the repulsive forces of electrons within the star eventually counter further gravitational collapse. The star cools; it releases its atmosphere in the form of a planetary nebula and dies peacefully. What remains is a star cinder we call a white dwarf. More massive stars explode as supernova; the star’s atmosphere is violently expelled into space while the core unable to hold itself up under its own weight, continues to collapse, shrinking to a point of zero volume called a singularity. All the particles, the atoms, neutrons and electrons which made up the star’s core are crushed out of existence and the gravitational attraction of the object becomes so powerful that nothing can escape, not even light. Needless to say, black holes are invisible but we know they exist because of the gravitational influence they have on their surroundings. Some black holes are in orbit around binary systems and astronomers can detect the effect of the black hole on its companion’s orbit. Black holes can also rip matter from the companion star, which tumbling into its hungry mouth gets hot enough to emit x-rays as the particles speed up and collide. In principle any object can become a black hole if it is sufficietly crushed. There is a critical radius for which this will occur for every object. The Sun would have to be compressed to about 3km in radius, the Earth about 1cm, and you and I to something smaller than a neutrino. Black holes are simply matter squeezed to extremely high densities but the black hole at the centre of the Milky Way is something a little different. About 27,000 light years from Earth, at the core of the Milky Way is a huge black hole. Our Galaxy’s nucleus lies in the direction of the constellation Sagittarius. Unfortunately, there is a significant amount of gas and dust in the plane of the Milky Way, so all visible light from this direction is blocked from view. However, with longer wavelengths like radiowaves and infrared we can penetrate the dust to garner a better understanding of the galactic centre. The centre of our Galaxy is known as Sagittarius A and from radio telescope observations we know that it is made up of three components. The first is Sgr A East, an expanding bubble of gas associated with a supernova remnant. The second is Sgr A West, a region of hot ionized hydrogen gas and finally there is Sgr A*. This is an area revealing the traces of shock waves from recent star explosions. There are also x-rays and gamma rays pouring out from the region and there is indication that a dense cluster made up of over 20 million stars are packed into a volume of about 3 light years across while at its centre is a supermassive black hole. Stars close to this black oblivion orbit it at some 32 million km/hr. They are moving so fast that even though they are very far away, their positions taken in infrared are seen to change within a matter of months. This orbit also tells us that the stars are in the grip of a monstrous object with about 4 to 5 million times the mass of the Sun yet contained in a volume of space a little less than the distance between Mercury and the Sun. Moving far from the raging black hole and out towards the halo, we come across vanishing stellar streams. These appear to be long filaments of stars all with a similar composition but moving at an angle relative to most of the other stars. More than a dozen such streams have been identified ranging in length from some 20,000 light years to as much as a million. Stellar streams are created when galaxies come too close to our own and are gradually torn apart by gravitational forces. The stars are pulled from the smaller galaxies by tidal waves until eventually all that remains of the galaxy are these vanishing stellar streams merging with the Milky Way. One of the most spectacular is the Sagittarius stream which extends over a million light years and bridges the Milky Way to the Sagittarius dwarf elliptical. One of the most studied is the Arcturus stream, located about 37 light years away, containing the star Arcturus. Arcturus and its stream is a remnant of a dwarf galaxy devoured long ago by the Milky Way. Just like many other creations of nature the Milky Way has consumed its way to its present size, swallowing up lesser objects through intergalactic cannibalism. The interaction of galaxies is not confined to greater galaxies devouring lesser ones. The light from M 31, the Andromeda galaxy, shows a blueshift corresponding to an approaching velocity of some 360,000km/h. This means that in about 4,000 million years time, just as the Sun is ending its own life and Earth has died long before, Andromeda and the Milky Way will collide. The stars in each galaxy will probably experience few collisions due to the colossal distances between them but the structure of both galaxies will be destroyed, perhaps forming a giant elliptical galaxy. If there is anyone about to call this galaxy home, a new story on the evolution of the Milky Way will begin. A Brief History If you’ve arrived this far, then a little history is in order. It’s amazing to think that our understanding of the universe, a huge amount of expanding space generously littered with thousand of millions of other galaxies is a rather recent story, no more than a hundred years old. At the beginning of the last century, astronomers were still debating the nature of nebulae, those fuzzy, spiral shaped clouds found all over the night sky. Were they part of the Milky Way or were they galaxies like our own but very far away? The story of galaxies probably began back in 1750 when Thomas Wright reasoned that the Milky Way formed a disc made up of thousands of stars and that the Sun was not at the centre of the disc but out to one side. He went on to suggest that the cloudy blobs of light seen in the night sky probably resided outside the Milky Way. Kant called them island universes. By the late 18th century astronomers were eager to find comets which were easily mistaken for the fuzzy nebulae. Careful cateloguing became essential and two observing masters, Messier and Herschel, plotted many such nebulae. Indeed, Herschel positioned some 2,500 most of which are now known to be galaxies. Over the following decades, many nebulae were resolved into clusters, others were identified as glowing clouds of gas within the Milky Way. But the spiral structured nebulae remained a mystery. Many astronomers at the beginning of the twentieth century would still agree that they were interstellar clouds of dust and gas. In the 1920s, Edwin Hubble, using a 100" telescope, detected variable stars in several nebulae. His discovery was revolutionary because now distances could be measured. Variable stars have a characteristic pattern resembling other stars called Cepheid variables. Henrietta Levitt, had shown there was a correlation between the period of a Cepheid variable star and its luminosity, its intrinsic brightness. By knowing the luminosity of a star it is possible to measure the distance to that star by measuring how bright it appears to us. The dimmer it appears the farther away it is. Thus, by measuring the luminosity of these stars, Hubble was able to show that the nebulae were not clouds within our own Galaxy, but were external galaxies far beyond our own. Hubble's second revolutionary discovery was based on comparing the measurements of these galaxy distances to the recession velocities, or redshift of them. He showed that more distant galaxies were moving away from us more rapidly. When these two discoveries were put together, it dawned on astronomers that the universe must be expanding. Hubble’s work marked the beginning of modern cosmology. Looking Out From Home There’s a useful principle called the Copernican Principle. It accepts that Earth is not at the centre of the universe but moves around the Sun which in turn is not at the centre of the universe but is quite an ordinary star, occupying no privileged position in the Milky Way, let alone in the universe itself. The principle is useful for it allows us to infer the likelihood of the nature of the universe. If the Earth and the Sun are occupying no special place and the Sun appears to be a pretty ordinary star as far as stars go, then in like manner so too with the Milky Way. It must also be pretty similar to other spiral galaxies. It was one of the justifications of the Hubble Telescope to put this inference to the test by calibrating Hubble’s Constant – the redshift or recession velocity of galaxies known to describe the expansion of the universe – and then measuring the angular diameter of a good number of galaxies resembling the Milky Way to determine average size. Needless to say, in agreement with our principle, the Milky Way was found to be a pretty ordinary spiral just a little smaller than average. Another key insight of Hubble was to note that there were different kinds of galaxies of which spirals were just one. Following this discovery, all galaxies are defined according to shape. Hubble is credited with creating a classification scheme for galaxies, which is usually referred to as the Tuning Fork diagram. Spirals Spiral galaxies usually have two main parts. The first is a flat disc containing a lot of gas and dust between the stars which means quite a bit of star formation is taking place within the disc, particularly in the spiral arms where we find a lot of hot, young stars and their clusters and a large bulge component consisting of old Population II stars related to the globular clusters. Spirals are further sub-divided into regular spirals and barred spirals and then further sub-divided depending on the size of the central bulge and how tightly the arms are wound around the centre. The ‘a’ group has large bulges and tightly wound spiral arms and the ‘c’ group have almost no bulge and very loose arms. The Milky Way is somewhere in between and because we cannot really see the Milky Way, it is loosely classified as a ‘b’ and ‘c’ type spiral galaxy. The ‘SB’ group has a large, well defined bar that passes through the bulge with subclasses of a, b, and c. The Milky Way is believed to also have a bar, so is finally classified as a SBb or perhaps SBc type spiral galaxy. Lenticulars Some galaxies have no spiral arms and these are called ‘S0’ or Lenticular galaxies. Lenticulars are spiral galaxies without spirals. That is, they are disc shaped galaxies but where stellar formations have stopped and so consist of mainly old population II stars. For all intents and purposes, they can hardly be distinguished from ellipticals. Ellipticals Elliptical galaxies are the cosmic rugby balls of the universe. They are typically smooth looking and ellipsoidal in shape and unlike spirals, do not seem to rotate as a whole. Elliptical galaxies appear to have very little interstellar matter between the stars and so consist mainly of old population II stars. Most Elliptical galaxies are small and dim and are sub-divided according to how flat they appear. The letter ‘E’ is followed by a number, bigger the number flatter is the galaxy. Irregular Irregular galaxies are where all the other types go for they have no definite stucture. Often distorted by the gravitation of their intergalactic neighbours, these galaxies typically exhibit peculiar shapes. Some irregulars have a lot of dust and gas so star formation is possible. Others have very little star formation going on. Messier's Galaxies When it comes to observing galaxies, Messier’s list is a good place to begin. These can be grouped into two main categories: Spring Galaxies and Autumn Galaxies. Spring Galaxies in Virgo: M 49, 58, 59, 60, 61 84, 85, 86, 87, 88, 89, 90, 91, 98, 99, 100. Galaxies in Leo: M 65, 66, 95, 96, 105. Galaxies in and around Ursa Major: M 51, 63, 64, 81, 82, 94, 101, 102, 106, 108, 109. Autumn Andromeda - The Local Group: M 31, 32, 33, 110. Pisces: M 74. Cetus: M 77. The Messier galaxies can also be placed into their respective types: Spiral Galaxies M 31, 51, 58, 61, 63, 64, 65, 66, 74, 77, 81, 83, 88, 90, 91, 94, 95, 96, 98, 99, 100, 101, 104, 106, 108, 109. Lenticular Galaxies M 84, 85, 86, 102. Elliptical Galaxies M 32, 49, 59, 60, 87, 89, 105, 110. Irregular Galaxies M 82, 51B NGC Galaxies It is also of interest to work through some non-Messier galaxies. Here I've included some of the brightest galaxies in the night sky and should have a magnitude brighter than 10. Autumn Spirals: NGC 253, 891, 1055, 7331, 7479. Irregular: NGC 6822 Winter Spiral: NGC 247, 253, 613, 1023, 1232, 1398. Eliptical: NGC 185, 1395, 1407. Spring Spiral: NGC 2403, 2683, 2841, 2903, 3184, 3344, 3521, 3628, 3953, 4490, 4526, 4535, 4565, 4559, 4571, 4631, 4656, 4699, 4725, 4753, 5005, 5068, 5247, 5907, 6946. Elliptical: NGC 3115, 3384, 3585, 3607, 4125, 4494, 4636, 4697. Lenticular: NGC 3115. Irregular: NGC 2976, 3077, 4214, 4449, 5195. Summer Spiral: NGC 5866, 6946 and of course, the Milky Way band of stars. What to Expect There is a kind of deep space disappointment for many beginners when they set out to observe galaxies. Perhaps they rightly expected to find more than a smudge of light at the eyepiece, perhaps they expected Hubble like images. But just as music is interpreted on the silence built around it, so to with observing galaxies. As sometimes happens, those moments in deep space when you have eventually caught a galaxy and you can say to yourself, “I’ve seen it! I’ve finally made visual contact with an object millions and millions of light years away”, remains much more than just a moment. If there is something as grand as an art to galaxy observing, it may consist in nothing more than being sensitive to each moment, wholly receptive and regarding that moment as utterly new and unique. Here are just a few sketches of galaxies taken with a 10" to give some idea of what to expect. Sketches with a 10" And here are a few more sketches but this time along with Hubble like images to get a feel for comparison.M104NGC 3953NGC 3184NGC 2903NGC 3226/7NGC 2683NGC 2859NGC 2964/68M 109Observing Tips As with many things in life, observing galaxies is dependent on many variables, not least of which is experience. Within reason, the more you practice, the more you will see. Assuming you’ve already got your telescope and eyepieces, some general advice can be offered. Needless to say, there are many threads on SGL which cover these points in more detail. Stellarium - useful for planning sessions, seeing what is about, learning the positions of constellations and much more. Star Atlas - quite literally, you’ll be lost without one. RACI Viewfinder - helps when it comes to hunting out deep sky objects. Telrad or Rigel - helps to aim your scope in a given part of the night sky. Low Magnification Eyepiece - your star-hopping workhorse. Observing Chair - to be patience you need to be comfortable and so you need to be seated. Red Light - helps retain night vision when you need to see something like your map etc. Eye Patch - keeps both eyes open while observing, since squinting strains the working eye. Light Pollution - the single worst enemy for stargazing is light pollution. A small telescope in the countryside will show faint objects better than a larger scope in the city. In effect, darker the night skies, brighter the deep sky objects. Dark Adaptation - the human eye takes time to adjust to the dark. If you have planned an evening with deep space objects, try not to observe any bright celestial object such as the Moon or planets with your working eye. It’s best to let your eyes adjust to the dark for 30 min or so before starting a galaxy observing session. This will give the rods in your eye time to adapt, for very faint objects like galaxies cannot be seen easily with the cones. Clothing - you’re observing at night when it is the coldest, when the body and mind is most sensitive. Effective protection requires three-layer clothing. The inner layer should be made of cotton or synthetic microfiber. This will help absorb sweat. The middle layer is made of heat insulation material to keep body-heat cocooned. The outer layer transmits water vapour to the environment and keeps out the wind. Also, pay particular attention to your hands, feet, head and neck. Averted Vision - looking directly at deep space objects might not be the best method for observing them. Practice by centering a dim star or DSO in the centre of the eyepiece’s field of view and concentrate your attention on an area just a little off to one side or above. Alternatively, place the object a little to the side or below the centre of vision. Either method should work, but finding your sweet spot will be a matter of trial and error. Don’t Squint, Jiggle and Breath - try not to squint when observing celestial objects, for by doing so you are not only straining your working eye which can lead to fatigue but also limiting your powers to detect faint objects. There may also be occasions where you are certain you have the specific area where you think the deep space object resides but it appears to be lurking under the limit of visibility. If this is the case, tap the telescope or eyepiece just a little to make the field of view jiggle. It’s not guaranteed but you might find the object revealing itself. Again, when you are concentrating you might find yourself holding your breath without realizing it. Limiting the oxygen to your brain, even for just a few seconds, compromises night vision. So while observing its good practice to breathe steadily and deeply but in a calm and relaxed fashion. Aperture and High Power - when it comes to viewing deep sky objects, aperture rules. Sketching and Log Book - better to be a visitor, rather than a tourist. There are two essential features to visual astronomy. The first is to find the object and the second is to observe it. The former process involves star-hopping and reading star maps, the latter requires you to slow down and to engage yourself with the complexity and beauty of what is being observed. It's been said many times before but anything glanced at will always look like a featureless something or other but the trick is to go beyond this style of looking and practice picking out features and textures. It is important to slow down from time to time and sketch or write about what you are seeing. Planning - a session is a good idea and part of this is to check out sketches by other observers. Drawings should give you an idea of what the object will more or less look like if you were to use similar aperture and magnification. Patience - master patience you'll be master of yourself and the night sky is a good teacher. If you don't succeed one night, or you can’t go out for weeks on end, don't be down hearted. In most cases, during that time you've probably discovered something new about yourself and those stars and DSOs will be back to give you another chance, another night. Cloudy nights - stargazing is a hobby that can be a tiresome road and one can suffer for it and be grieved, but the worst you can do is add to this frustration and curse those things beyond your control. Cloudy or uneventful evenings are just that, nothing more and when older they will appear as a singular, non-descript events, yet shining from them like a host of gleaming stars will be those evenings where everything just seemed perfect and the universe, at last, could murmur to you its secrets.
  9. 79 points
    Happy New Year Everyone. So finally after 9 months processing, which included a full redo of the RGB blend, I have finished the 2nd Mega Mosaic to complement the 400hr Orion Mosaic myself and Olly made. This mosaic began in 2012 where I collected 30 panes of Luminance. In 2013 I completed 2 rows of RGB. Later in 2015 while taking imaging trips at Ollys in Les Granges, I finished the RGB panels, and I took Ha data to blend into the central rift area. I also took an extra LRGB column on the left hand side of the image. Like the Orion mosaic, this had data at 0.53m with added 1m resolution data for the Eagle, Swan, Lagoon and Trifid nebulae. Again this is the highest resolution image of this area of the sky as far as I am aware of. Thanks Tom. Flickr image can be seen here. https://www.flickr.com/photos/28192200@N02/24086292076/in/dateposted-public/
  10. 78 points
    Just a few of the goodies ive had from the 130pds over the past few months:
  11. 77 points
    A true dark site is not "pitch black". Once your eyes are fully dark adapted the sky is markedly bright with stars, Milky Way and natural airglow. Moving around without any artificial light is easy. A lamp is only needed for seeing small objects, reading etc. Foreground objects (trees etc) look truly black against the bright sky. In a telescope at high power, the sky background looks truly black (you can't see the eyepiece field stop). After viewing for some time, when you look up at the sky again it's dazzling (you need to shield your eye from it while looking through the eyepiece). At a light polluted site it's very different. The eye adapts to the ambient light level (dictated by the pervasive glow of streetlights etc, even if not directly visible). Under those conditions a clear sky can look "pitch black", but only because the eye can't adapt fully. So apparent blackness is not a good test of sky quality, it only tests dark adaptation. The test is limiting magnitude. If you can see stars down to 4 mag then you should manage a few bright DSOs in a telescope (e.g. M31, M42, M57, M13, M81/82). If you can see to 5 mag then you'll see many more, and the Milky Way may be visible. If you can see to 6 mag then the MW will be clearly visible and you'll be able to see all the Messiers above your horizon with a 100mm scope (or smaller), and all (or nearly all) above-horizon NGCs with a 12". If you can see stars fainter than 6 mag then you have very good eyesight. Light pollution is of three types. One is direct glare from steeetlights etc. You need to shield yourself from that, e.g. by choosing your viewing spot, putting up barriers etc. Two is ground light reflected off walls etc; you can't see lights directly but your garden is indirectly lit up. Shield yourself by putting a hood over your head at the eyepiece and give your eye time to adapt. Three is skyglow caused by ground light reflecting off water vapour in the air. This limits the faintest stars you can see, and there's nothing you can do about it (unless you find that a "light pollution filter" works for you). "Nebula" filters (OIII, UHC etc) are effective on emission nebulae (e.g. M42, M1) but have no effect on other types of objects, i.e. clusters, galaxies (note for pedants: there can be some slight effect on a handful of large galaxies at a dark site, e.g. M33). At a light polluted site the easiest DSO types are open clusters, bright globular clusters (e.g. M13), bright planetary nebulae (e.g. M57, Eskimo, Cat's Eye). Diffuse nebulae (emission or reflection) are generally more difficult, though with a few bright exceptions (e.g. M42), and galaxies are generally very difficult, again with a few bright exceptions. The reason for all this is that light pollution hurts the limiting surface brightness of a scope more than limiting stellar magnitude. For example see Figure 18 of this paper: http://arxiv.org/pdf/1405.4209v1.pdf A telescope can't improve the surface brightness of a target, and most galaxies are of about the same surface brightness as the Milky Way. So if you want to see galaxies well, you need to be able to see the Milky Way with the naked eye.
  12. 76 points
    I've recently come across this piece on the web written by Alan MacRobert from the well known and respected astronomy magazine Sky & Telescope. It is well worth a read if you are thinking of getting into the hobby - ideally before you leap in and buy a telescope : https://www2.wwnorton.com/college/astronomy/astro21/sandt/startright.html As someone who has been in the hobby for many years now I found that many of the hints, tips and pointers in this article are right "on the button". John
  13. 73 points
    I don't profess to be either an expert or an expert speaker but was asked to do a couple of talks at the Peak Star Party recently. I have attached below my written handout notes for each session in the hope they will help the odd person with how to find objects in the sky and also how to ensure you get the best views when you do find them. These notes are based on my own experience and also information gleaned from many sources since I started observing; thanks to anyone who recognises their work or comments. If one person finds them useful then I'll be delighted and it's been worth the minor effort uploading them. They have been put into a couple of other threads but I felt they were somewhat hidden and might be more easily located here. Cheers Shane Locating Objects in the Night Sky.pdf Collimation of Newtonian Telescopes-1.pdf This post has been promoted to an article
  14. 71 points
    Preface The purpose of this post is to provoke a basic understanding of Mars which will not only help ignite further interest in the red planet but also aid planetary observations when out in the field. In this manner, I have divided the entry into two main divisions. The first deals with some of the more important features and characteristics of the red planet while the second entry deals with observing Mars. Part One: A General Understanding of Mars 1 – General Introduction Mars is a barren and cold planet orbiting the vast darkness of space. It is a world of undulating landscapes, jagged rocks and arid hills. It is dry, dusty and desolate; its air is thin and extremely cold. You probably wouldn’t want to live there for long. There are dust storms that can darken the skies for months and every night temperatures drop to about 140ºC below zero and the days rarely see better than 15ºC. Since the beginning of the historical record, every major civilization has been captivated by the red planet. Ancient cultures worshiped Mars and typically understood it as foreshadowing chaos and catastrophe whilst more recent cultures have believed it could harbor life and even advance civilizations. Today, we see an old and weathered world, a place with ice caps, wind sculptured rock and dusky continents, but a world no less fascinating than those conjured by past civilizations. The ancient Egyptians named their grandest city after the planet; Al Qahira, the Vanquisher, an old Arabic term for Mars which over time changed to Cairo. For Asian cultures, Mars was the fire star, a portent of grief and murder. The Greeks of the Polis called Mars Ares, the son of Zeus whose sons were Fear (Phobos) and Terror (Deimos) from which Mars’ own two moons have been named. The planet itself is named after the Roman God of war, hostility and unrest whose sons Romulus and Remus founded the city of Rome. 2 – Distance, Orbit and Seasons Mar’s average distance from Earth is about 228 million kilometers, hurtling through space at around 86,500 kilometers an hour. If you drove a steady 120km an hour, the legal limit in most European countries and never stopped, you’d expect to arrive within 216 years. A Martian year is 687 Earth days long, and a Sol or Martian day lasts 24.6 Earth hours, or 39 minutes and 35 seconds longer than here on Earth. The planet’s orbit is so eccentric – the most eccentric of any planet apart from Pluto - that there is quite a variation in surface temperatures ranging from a mild maximum of 27ºC to an unforgiving minus 140ºC. Putting this into some perspective, the lowest recorded temperatures on Antarctica, the coldest place on Earth, have been around minus 90ºC. Typically, the low albedo regions, the darker areas you see through a telescope, are warmer than the lighter northern or southern regions. Although the Northern Star on Mars is the supergiant Deneb, Mars’ axial tilt is in fact very similar to our own which means it experiences similar cycles of seasons. However, due to its eccentric orbit they’re twice as long as on Earth. Breaking down the seasons into their respective hemispheres, we end up with the following durations: Southern Hemisphere Northern Hemisphere DurationSpring Autumn 146 days.Summer Winter 160 days.Autumn Spring 199 days.Winter Summer 182 days. 3 - Mass, Volume and Atmosphere In one respect Mars is similar to the Moon in that one side is heavily cratered while the other is not. It is also similar to Earth in that it has seasons, an atmosphere of sorts, and weather. There are clouds here and winds and evidence that rivers once flowed and flooded the ancient lands with water. It’s also about midway between the Earth and Moon in size, measuring around 6,800km in diameter. In terms of volume about six Mars’ globes could fit in one Earth. Its mass is just 11% of Earth’s and it has 62% less gravitational force. This mix of low density and smaller size make things lighter on Mars. Objects fall slower, where a ton of soil would weigh about 370kg. The gravity on Mars is just a third of Earth’s but it is still sufficient to allow the planet to retain a tenuous atmosphere. This toxic layer surrounding the red planet rises to almost 11km high, some 5km more than on Earth and consists of 95% carbon dioxide, 2.7% nitrogen, 1.6% argon and a smattering of oxygen, water, and methane. The thin atmosphere has allowed Mars to be relentlessly attacked by space debris which would have been vaporized in our denser atmospheric veil. Like the Moon, Mars’ surface has been bombarded with impunity and its wounds and scars are evident across the entire surface. Martian air is made up of the same stuff we have on Earth but there is death for us in it. On Earth, roughly 75% of our atmosphere is nitrogen, 23% oxygen, 1% argon and carbon dioxide makes up only 0.05%. What oxygen there was on Mars, so precious to life on Earth, has been used up, transforming the iron rich planet into a rusty oxidized red. Considerable quantities of methane have also been found in the Martian atmosphere. A single plume can release over 40,000kg of the stuff in a single day. Methane appears to rise during the warmer spring and summer months and is distributed in large plumes over volcanic regions such as Tharsis, Elysium and Syrtis Major. The implications of methane is interesting for on Earth it is a greenhouse gas typically released by tiny organisms present in rotting vegetation and the stomach of certain animals like sheep and cows. The existence of such a gas has sparked renewed interest in the possibility of some kind of micro life on Mars, yet we must temper this possibility with the knowledge that methane can also be produced by purely physical, non-biological processes. 4 - Retrograde Motion In a world before electricity, people had no more than flame to light their way. Night was a blanket of darkness and Mars would have stood out more than almost any other object. In the dark, the world is not the same; the absence of light skews estimations and fires the imagination. You would see this blood red planet glaring down, distant and vaguely menacing, at times demonically possessed as it would start shifting from its forward motion and wander backwards like no other object in the night sky. Little wonder that Mars had such notorious fame. This phenomenon of Mars going backwards is referred to as Retrograde Motion and to get an idea of what is going on we can imagine the planets in our solar system racing around the Sun on a cosmic sized race track. On the faster inner lanes are Mercury, Venus, Earth and Mars and on the slower outer lanes are Jupiter, Saturn, Uranus and Neptune. From Earth’s perspective, we see Mars racing around a relatively slower outside lane and for most of the time the background stars and Mars are moving in the same direction relative to us. However, we are racing around the Sun on a faster lane, so at some point we are going to lap Mars and as we approach and then pass the red planet, for a brief period, in fact every two years as we approach Mars’ opposition, from our line of sight it actually looks like Mars is going backwards. As we draw further away from the planet after opposition, our line of sight alters the apparent course of Mars and it appears to recommence its slow eastward path. It is so simple to explain, but in fact took thousands of years and some of the greatest minds ever to find a mechanical explanation for Mars’ bizarre orbit. In the end, it needed a radical new way of thinking, a heretical paradigm shift for which people were burnt at the stake for believing; an idea which placed the Sun at the centre of the Solar system. 5 – Regolith The ochre hue we see of Mars is due to rusting. Over the slow march of billions of years, any oxygen there was on the planet has caused the upper layers of the Martian surface to rust and disintegrate into a dusty iron oxide. On Mars as well as the Moon and Venus this surface material isn’t referred to as sand, soil or dirt, but regolith. The word stems from the Greek rhegos meaning blanket and lith meaning rock. As such, regolith, regardless of its material composition, is a form of very loose, ground up rock spread over the bedrock of other worlds. Most of Mars’ regolith is a very thin, highly toxic layer of oxidized dust which is so finely ground that its particles are as fine as cigarette smoke and when winds whip up it can stay suspended for months often causing surface features to appear muted and obscure. Martian regolith creates dunes similar to those on Earth and dust devils frequently loft high into the atmosphere, whipping violently across the wind sculptured terrain. These spinning vortexes are formed when cold air drags the surrounding warmer air upwards creating huge columns of dust, some of which can rise to over 10km in height, stripping the terrain of its brighter surface dust and leaving behind dark streaks and trails. Regolith may help shape and transform the surface of Mars but wind is the primary process of erosion as it cuts into the landscapes creating grooves, ridges and yardangs – streamlined hills carved by the wind. Mars is said to suffer from Low Thermal Inertia which means its surface heats up quite quickly in daylight. As there are no lakes or oceans to quell this effect with clouds, when the Martian land heats up, hot air rises and is replaced by cooler air. This cocktail of lower pressure air rising and a mass of cooler air racing in to replace it causes winds. Typically wind velocities on Mars are reckoned to be anything from a mild breeze to gales of around 150km an hour. 6 – Water Traces of water vapour in the atmosphere is a 1000th of that on Earth but even this small quantity is sufficient to form clouds and coat areas of the Martian surface in frost during the long winter chill. Mars’ low pressure prevents water molecules existing in liquid form, so when temperatures rise above freezing point, the ice and frost sublimates into vapour. From Earth the plumes of cloud, fog or ground hazes can appear as bright, transient features often covering low lying lands such as valleys and canyons and atop larger volcanic areas. Ice and dry ice exist at the poles. Carbonates have also been found which may contain the fossilized remnants of stromatolites. Such fossilized microbes have been discovered in Australia dating back to 3.5 billion years ago, so there might be the chance of finding such microscopic Martians on Mars some day. It’s a long way from the Martians of science-fiction but even the discovery of such tiny microscopic life forms on another world produced from the wonder of amino acids would be significant, perhaps as significant as the Copernican revolution that put the Sun at the centre of the Solar System and many at the burning stake for believing such things. 7 – Core and Magnetic Field No ghostly auroral displays grace the Martian skies and a compass here would be useless. If the existence of a magnetic field is a good indicator of a geologically active and living world, then Mars died long ago. There is no fluid molten iron at the planet’s core and any dynamo effects the planet ever had ceased billions of years ago. Mars’ core in now inert but evidence in rocks suggest that its original magnetic field was about a tenth of Earth’s and was lost in the late heavy bombardment period. Certainly, no impact craters after this time show signs of magnetism. Mar’s core mass is estimated to account for 6% to 20% of the total mass of the planet and is primarily made up of nickel-iron surrounded by a silicate mantle and then a rocky crust similar to the basalt found on Earth’s oceanic crust. The Martian magnetic field shut down may have been due to a gradual cooling and solidification of its core, or a more violent consequence of asteroid impacts which generated such tremendous damage that Mars’ liquid core lost incredible amounts of heat and the ability to flow coherently. 8 – Timescale Periods Even if Mars never sustained life, it has been alive geologically speaking. There is profound evidence of weathering, enormous flood areas the size of Europe, dried up river deltas and extinct volcanoes. Lava, wind and water have all worked upon the tortured surface. Mars presents to us a record of the vast period of time during which these natural powers were exerted. There are enormous mountains which have been produced by volcanic action, and in like manner, there are huge valley systems which teach us not merely the power of moving water, but furnish us with data for estimating the enormous lapse of ages during which that force operated. Deep and long ravines have been spied that have required aeons for nature to create, and yet even the sum of these years is nothing, as if merely the work of yesterday, when compared to the antecedent periods, of which there are also monuments. In this respect, although Mars has never been subject to plate tectonics, its surface has not only been sculptured by water and weathering but also by the severe punishment of meteor and asteroid impacts. It is estimated that about 60% of Mars’ surface is cratered and that there over 300,000 craters larger than a 1km in size. A general timescale of Mars is based on crater density and stratography. This scale has been worked into four distinct stages: Pre Noachian Period – 4.5 to 4.1 billion years ago. This is part of the late heavy bombardment period and one of the most violent stages in Mars’ life. It was probably around this time that the Borealis Basin and the Hellas Planitia were formed, two huge impact craters created when asteroids 60% the size of the Moon came crashing into the red planet. Around this time the Martian magnetic field shut down and the Solar wind started stripping away the atmosphere. Noachian Period – 4.1 to 3.7 billion years ago. This is known as the wet and warm period when water lakes covered large areas of the Martian surface. By the end of this period, Mars had probably lost most of its atmosphere and water resulting in the dry and dusty Mars we know today and the formation of dry lake beds and deltas around Arabia Terra. Hesperian Period – 3.7 to 3 billion years ago. Volcanoes erupted over the Martian surface, especially in the Tharsis region. Huge quantities of baslatic magma flowed from Mars’ interior creating the enormous shield vocanoes we see today like Olympus Mons. Amazonian Period – 3 billion years ago to today. This period saw the end of Mars’ more active age and the beginning of its long retirement. There was the dwindling of volcanic activity, the disappearence of most of its water and atmosphere, and the significant reduction in asteroid or meteor impacts. 9 – Outstanding Martian Features Any brief tour of the Martian surface should highlight the following features. The Tharsis region is home to some of the largest mountains in the solar system. Olympus Mons is part of this area and is the tallest known mountain anywhere. Over three times the height of Everest, the now extinct volcano soars 22km into the thin air with a base width of almost 600km. If water surrounded it, the ancient shield volcano would be the size of a small island, very similar in structure and form to those making up the islands of Hawaii. Near Olympus, spanning the planet’s crest diagonally are three older volcanoes, Arsia, Pavonis and Ascraeus Mons and although smaller in size were no less violent, generously adding to the basaltic smothered area of Tharsis. Most volcanic activity occurred between 2 to 1 billion years ago, finally spluttering out around 200 million years ago. It is due to this extensive volcanic activity that you find the northern hemisphere is sparsely cratered relative to the south. Tharsisian lava flows simply filled in many craters; some so completely that what remains are ghost craters similar to those on the Moon. Valles Marineris is the largest valley in the Solar System. Named after the success of the Mariner 9 voyager, it is a gigantic gash stretching east from Tharsis along the equator and takes up about a quarter of the planet’s circumfrence. It was formed when the local crust could no longer take the pressure from the growing volcanic Tharsis region and simply collapsed upon itself resulting in a huge channel some 4000km long, 200km wide and up to 7km deep. By comparison, the hive of canyons, gorges and valleys that make up the majestic Grand Canyon in Arizona is dwarfed by Valles Marineris. To the north of Valles Marineris back to the northern part of Tharsis, we come to Alba Patera Mons a huge but relatively flat volcano. Its outflow forms an ellipse which spans roughly 1400km. It is the largest known lava factory in the Solar System. Other notable volcanic regions include Elysium and Syrtis Major which has its own volcanic beast about 1000km wide and 3km tall. The prominent dark shade of this area comes from the basaltic rock of the region and the relative lack of dust. The Borealis Basin takes up almost half the northern hemisphere and was likely the result of a huge, planet crushing impact. As such it is a monster crater, the largest in the Solar System which required something like the size of Pluto to smash into Mars. The consequence of such a violent outrage is believed to have finished Mars’ magnetic field for good. Hellas Planitia in the south is another huge impact crater roughly 2300km wide and around 7km deep. It is so deep that even lacking Mars’ atmospheric pressure that makes it impossible for water to form, there is enough pressure down here to allow liquid water to exist. If you draw a line from Hellas Planitia and follow it through Mars’ interior, you’ll end up in the area of Tharsis and its gigantic volcanoes. Scientists now believe that the impact at Hellas was so great that the seismic shock wave helped form these features. Space probes have revealed a number of caves on the Martian surface, most notably on the sides of volcanoes. These caves are thought to be treacherous shafts produced by collapsing ash and balsatic deposits. The Seven Sisters are the largest known caves on Mars, found on the flanks of Arsia Mons in the Tharsis region. These have been measured to have entrances around 250m wide and descending to roughly a kilometer. No doubt they will be found to run deeper, especially if these caves extend along the now extinct lava tubes. Mars is also home to two icy polar caps made from a mix of carbon dioxide ice and water ice. Most of the water on Mars is locked up in these caps and it is estimated that if all the ice melted, Mars would be covered by an ocean averaging 11 meters deep. Clouds and ice-fog form as the Sun climbs during Mars’ spring and summer. Atmospheric pressure is too low for the ice to melt and become liquid, so the water and carbon dioxide vapor rises through the process of sublimation forming clouds and a brilliant haze as seen from Earth. By winter the vapor freezes once again awaiting another new seasonal cycle. The North Pole measures some 1100km across and about 2m thick while the Soth Pole is about 4000km across with a thickness of around 3km. In comparison to the flatter and smaller North Pole, the southern cap is a landscape of pits and troughs, ice dunes and even geysers. The Kasei Valles is Mars’ largest outflow channel probably caused by water melting in underground reservoirs of ice. Some 3000km long and 230km wide, most of the Kasei Valles formed during the Hesperian periods some 3.5 billion years ago. To create such a system, scientists have estimated that a volume of water equaivalent to a global ocean about 1km deep was required with a discharge rate of up to 1000 million cubic metres of water per second. Certainly, Mars wept as it was dying. Oceanus Borealis is a hypothesised ocean that may have covered a third of Mars but which has long since disappeared. As the climate on Mars cooled the remnant of this speculative ocean froze over and was eventually absorbed beneath volcanic ash and dust. If the ocean ever existed, it is pressumed to lie hidden beneath the plains of Vastitas Borealis. Ancient shorelines have also been identified around Shalbatana Vallis which shows evidence of an ancient lake whose area was some 210km2 and about 460m deep. Large quantities of ice more than likely lie beneath the surface in areas far from the poles. Dust and ash cover the ice from imaging but its presence has been confirmed by space probes. Dark streaks of brine still ooze along narrow channels and can grow as much as 20m a day. By winter these streaks fade away as temperatures drop too cold for even brine to remain in liquid form. Part Two: General Observations 1 – Observing Considerations and Magnification Famed for being such a violent and war-like character, it’s quite ironic to note that Mars is relatively small planet made up of very delicate and subtle shades of oranges, browns, slate-blues and whites. For the observer, nothing really stands out like it does on Saturn or Jupiter and because Mars only comes into opposition once every two years, most of us simply don’t have enough practice when it comes to observing the red planet. A given session may reveal nothing more than a bright ocher globe, perhaps if we’re lucky a dark blob or two on its surface through the murky, unsteady haze of our own and Mars’ atmosphere. We browse a detailed Martian map only to find it too difficult to identify what we were looking at, which side of the planet our telescope was focused and even on some nights where the poles were to tell north from south. Following such frustrations, it should come as no surprise to understand why many astronomers find Mars quite a disappointing planet. Nothing is given in astronomy, especially when it comes to viewing Mars. Jupiter is about three times the size of Mars and to see Jupiter with a significant amount of detail, we’ll need around 160x to 200x magnification which means that to get a similar view of Mars, we’ll need an outrageous 600x. As impressive as that sounds, we are never going to get the kind of viewing quality that can allow for this type of power. 99% of Earth’s atmosphere lies in a layer about 30km thick and you’re at the bottom of it looking up. Adding to this problem is the fact that most atmospheric disturbances take place in the first 15km or so from where you stand, exactly where Mars’ own light is being refracted by air cells causing shimmering in the eyepiece. If you view from an urban surrounding although light pollution isn’t going to affect your image quality too much, warm air coming from buildings and mixing with the cold night will also help to warp the image. So a compromise is needed. In terms of aperture, I feel that Mars begins to get interesting around 6” in a reflecting type of telescope and around 4” to 5” in a good refracting telescope. In terms of power, we’ll need 200x to 250x to start tweaking some significant Martian detail which still means seeing conditions will have to be very good. As such, Mars is not a particularly giving planet. However, there are other ways we can help ourselves. 2 – Time, Patience and Comfort Atmospheric conditions can wreck havoc on our observations. Light diminishes and turbulence increases the lower Mars appears relative to the horizon, so try to view Mars as high as possible in the night sky. Mars also requires time, patience and comfort. You need the patience to spend time at the eyepiece waiting for those brief moments of atmospheric stillness where everything is just perfect and comes into view. To have this kind of patience you need to be comfortable and so you need to be seated. This cannot be stressed enough. If you want to do some serious planetary viewing of Mars, do yourself a favour and buy or make for yourself an observing chair. At this junction, we can also point out the importance of sketching. Typically, the general advice for seeing more on Mars is to up the aperture a little or improve on the quality of optics and telescope’s contrast but of equal importance is to simply slow down. There are two essential features to viewing Mars: locating the planet and observing it. The former requires the technique of knowing where to look, the latter, asking questions about the object and recording them in either written or sketch form. Anything at a distance just glanced at will always look like a featureless something but the trick in visual astronomy is to go beyond this and practice seeing - picking out the subtle and yet complex features and textures of the given object. Sketching really aids this process, but so too recording the observation in written form or talking into a digital recorder etc. There's no right or wrong way of going about it, so long as you spend a little time on your Martian sessions really trying to observe rather than just looking. Contrary to what folk may happen to think, the point of sketching is not to create some beautiful rendering of the object itself, but rather to train your eye to see better. With practice, it's amazing what the eye and brain can do. Overtime you really start to pick out features that the casual observer simply cannot see. I'm so convinced about the power of sketching that I believe with a little practice and care it will add a virtual inch to your aperture. If you sketch while seated, you can add another 1" for being comfortable. That kind of power increase is priceless. 3 – Aphelic and Perihelic Oppositions A Martian day is a little longer than on Earth and it rotates on its axis once every 24.6hrs. This difference of about 40 minutes relative to our own rotation is quite handy in terms of observation. If you can observe Mars at the same hour on every clear night possible, you’ll note a subtle lagging towards the planet’s east as those features of the previous day come into view just a little later on each progressive evening. This difference amounts to about 9º of longitude east every day which means that over a period of about 40 days, you can complete a tour of Mars’ surface. The best time to observe these subtle changes on Mars is when it is at opposition. This occurs once every two years when Mars is opposite the Sun relative to our own orbit and is virtually 100% illuminated and at its largest apparent diameter for that given apparition. As we approach Mars’ opposition more dusky features and the bright glare of the polar caps come into view. However, not all oppositions are equally favourable. Aphelic oppositions place Mars further from Earth and the planet’s disc is generally around 15” arcseconds in apparent size. Perihelic oppositions, on the other hand, are what most amateur astronomers look forward to. The planet is closer to earth and its disc has now grown to an apparent size of roughly 25” arcseconds, so obviously appears a lot bigger. Armed with a small telescope, you can work out not only the seasons on the planet but how the tilt of Mars gives good indication of the type of opposition you can expect. When Mars is at an aphelic opposition, its North Pole is tilted towards the Sun, which means it is summer in the north while the south is in its extremely long and severe winter. At such times, northern features are easier to discern. When Mars approaches a more favourable perihelic opposition, the South Pole is tilted towards us, making the duskier features of the south more presentable. Here it will be summer in the south and winter north. The summer at such times is shorter but warmer, causing the southern polar cap to melt more rapidly than it does in the northern pole cap during its summer. By way of a rough estimate, when Mars is about 15” arcseconds in apparent size, 1” arcsecond is equal to about 450kms and when Mars presents itself as some 25” arcseconds, 1” arcsecond is equivalent to about 270km. 4 – Martian Maps and Albedo Features Looking at the array of Martian maps, you’ll find two general features, areas once thought to be seas and those once thought to be land. In essence these are just different albedo features, areas differentiated by apparent brightness caused by sunlight being reflected back from another world. The maps I include below are some of the best I have seen which reflect to various degrees what you will be likely to see when observing in good conditions. Seas are the lighter features and include Sinus Meridiani, Mare Erythraeum, Mare Sirenum (Sea of Sirens) and Aurorae Sinus (Bay of the Dawn). Lands are the darker features such as Syrtis Major, Arabia Terra, Amizonis Plasatia (Amazonian Plain). The north where the Polar Cap lies is known as Planum Boreum while the south is known as Planum Australe, the Northern and Southern Plain respectively. If it is summer in southern hemisphere on Mars, then the South Pole will be tilted towards us. If summer is in the north, then the North Pole will be tilted towards us. At a given opposition one of these poles will be visible but due to its relatively small size and the fact that it is shrinking due to sublimation caused by the summer Sun, it might be quite hard to see. If you do observe something big, bright and icy that you feel ought to be a polar cap, big, then it's more than likely Hellas, a huge impact basin which often fills with mist and fog and looks more like a polar cap than the Martian polar caps themselves. The most obvious dark features you'll see on a night of good seeing are Syrtis Major, Terra Sirenum and Terra Cimmeria covering some 5000km and the Cydonian and Erythraeum area. These albedo features all have distinctive shapes. For example, Syrtis Major is often said to resemble India or Africa with bright Hellas at the edge. Terra Sirenum and Cimmeria are more elongated, Erythraeum is a large and darker blob while Cydonia is rather curved. If the night’s seeing is favourable, you can also try to discern more subtle features. The Eye of Mars is near Solis Lacus which some observers say looks like a human eye peering back at you. You'll also be able to see Niliacus Lacus, Acidalium, Sinus Sabaeus and Sinus Meridiani which are quite dark and dusky areas of Mars. By contrast to these darker albedo features, predominately lighter areas are typically around the Tharsis region, home to the tallest mountain and biggest volcanoes in the Solar System. The volcanoes are so big that even from Earth with our small telescopes we are sometimes able to see clouds floating on top of them which in the eyepiece will appear as rather small misty-white patches. It really is well worth your time looking out for them. There is always a dusty haze in Mars’ atmosphere but sometimes you will try to look at Mars and even on a great night of seeing will not be able to see the albedo features with clarity. Martian desert storms are very unpredictable and extremely violent and you’re never going to know when the next one will come crashing in and cover everything. Usually these dust storms last a few days, but sometimes they last for weeks and even months. If you’re fortunate enough to see one, you might be able to note a significant brightening of the fiercer areas as the winds hurtle through the region kicking up dust devils and huge spiraling columns of Martian regolith. At the end of the evening, even if you cannot see anything on Mars and only experience a shimmering, blood red globe try not to feel too disappointed. Think how fortunate we have been are to even be able to experience another world out there floating in the vast darkness of space. For further reading I can recommend the following books: Destination Mars by Rod Pyle. Mars & How To Observe It by Peter Grego.
  15. 71 points
    First attempt and first clear morning after 2 weeks of bad astrophotography weather. Taken about 2 hrs before sunrise on 07/13/2020 The image still has some startrails from the comet stacking mode in DSS. I've used the comet stacking mode and normal stacking mode and blended both together in Photoshop to get the comet with its starfield rather than startrails. Difficult process to do this manually. If someone knows a method/software that does comet stacking with its starfield, please let me know. DSS failed me on several occasions using comet+star stacking method. Ken Equipment and image detail: Nikon d610 TS72 APO + TS72flat settings: 432mm, f6, iso400, 40min. Different exposures ranging from 30 sec to 5 sec. Tracking: Skywatcher Star Adventurer software: Stacking: Deepskystacker 4.2.2 Processing: Adobe Photoshop
  16. 70 points
    I took a photo of Betelgeuse in February 2019 just because it's a pretty star - Thought I'd take another to see if it really has dimmed as much as everyone says and the difference is very noticeable - (prime focus of a 7" refractor with a focal reducer bringing it to f 5.6. )
  17. 70 points
    Years ago in one of my first astronomy books I read that this cluster is now known to be ploughing through some interstellar gas and dust - and the book (now lost) had a picture showing the streaming 'wake' behind the stars as proof. Trying to bring this evidence of motion out in my own picture has become an obsession so whenever guests want to image the region I add new data to what I already have and push it even harder in processing. A couple of nights ago with SGL member Sandancer we captured a further 6.5 hours or so in the dual rig. Great! I don't know how much is in here altogether but it must be... a lot!! The processing is a bit but this rendition is all about that 'wake' and the cluster's movement. Olly Bigger one; http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-ZBmVMGT/0/X3/M45%20final-X3.jpg Full (if the link workls) http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-ZBmVMGT/0/O/M45%20final.jpg
  18. 68 points
    There is a section in the Code of Conduct that refers to the forum censor that is used to edit out profanities. Please read it and follow its dictates. This is a family friendly forum and there have been many instances recently where posters have deliberately included words that are obvious profanities that have been obscured by asterisks or other non-alphabetic characters. This is not acceptable - there is no reason to include such words in posts. Let's keep the forum suitable for our children and grandchildren and something we can all be proud of. Mike
  19. 67 points
    The MW from Perissa Beach, Santorini. Taken on my recent 23rd wedding anniversary trip with my lovely missus. Canon 6d/Samyang 14mm, bracketed image - sky 10 x 25s iso 800 stacked in PI, foreground 1 x 30s iso 800. Processed in PS. Hope you like it! Rich ?
  20. 65 points
    "It is not the employer who pays the wages. Employers only handle the money. It is the customer who pays the wages." Henry FordFirst Light Optics is only one month away from her seventh birthday. With your support we have grown from a single person working from home to a team of seven operating from two units on a business park in Exeter. We literally could not have done this without you so we are hugely grateful. Earlier this year we began wondering how we can give something back to the community. We already sponsor Stargazerslounge which benefits it's members and others searching for info. But many of our customers don't belong to this or any other forum. We considered emailing all our customers with a one-off discount code but that didn't feel right because it would benefit only those who were in a position to buy. Then Grant came up with a really neat idea - a weather forecast site dedicated to astronomers. There are of course other forecast sites available with an astronomy theme but often they use only a single freely available data source or, worse, simply scrape data from other sites. And they tend to be built on a budget so don't update frequently enough to be really useful or they provide limited information so you need to visit multiple sites to obtain a full picture. So we decided to build the best weather forecast site focused entirely on astronomy and to release it free of charge. Clear Outside Weather Forecasts for Astronomers Here are some key feature: Hourly forecasts, updated hourly. Easy to understand traffic-light indicators with a drop-down menu for those wanting more information. Without giving too much away we use an aggregate of a number of weather models including the UK Met Office, the Norwegian Met Office and the American NOAA. To provide the most reliable up-to-date forecast and long-term stability we have invested in commercial weather data services and a dedicated infrastructure. Detailed Sun and Moon rise, set and meridian data are accurately modelled on your location. Similarly we have integrated ISS pass over times and other info modelled on your precise longitude and latitude. For more information please click the 'How to Use' button and take the tour. We have also included a 'Contact Us' page where you can make suggestions and leave feedback and a ‘Road Map’ page where we will detail upgrades and developments we are working on. It is our gift to you the astronomy community for your support over the years. We hope you like it Regards, SteveG, Annette, James, Grant, Lisa, Martin & SteveB.
  21. 65 points
    This has got to be THE single most iconic image out there - So thanks to Hubble there's masses of pressure with this image! How can you improve on an icon? I have no idea at the moment! But the mono Ha data has come out OK! This is a low one for me - Only gets to 37 degrees maximum and I was just starting to only image above 40 degrees I will be collecting the OIII and probably SII as well (depends on how a bi colour comes out) - But meanwhile I thought that this stood on it's own two feet as a mono target. It was a delight to process as the data is nice and strong. Details: Mount: Mesu 200 Scope: Orion Optics ODK10 Camera: QSI683 with 3nm Ha Astrodon filters 28x1800s 14 hours in total. You can see the larger res image here
  22. 63 points
    I havent posted for a while its so good to finally get going again..... Ive been wanting to image a wide field of M45 for years.... managed to get tenough over the past 4 weeks now it is rising early in the morning.......total 12hrs comprised of 300s, 180s and 60s exposures. Imaged with a 105mm 1.4 Sigman lens @ f2 with an ASI2600 OSC. Cmos Processed in Pixinsight, Photoshop,and lightroom Thanks for looking Peter
  23. 61 points
    Hi all, this has been a tough slog. Starting in August i intended to just shoot Barnard 150 and well i just kept going. I really have no idea how you guys with mono cameras manage mosaics, hats off. Shot over 9 nights and a total of 31 hrs in 150 second subs. Esprit 100, Zwo 071 pro, mounted on an AzEq6 Captured using SGPro, stacked in APP. Processed in APP, PI and PS. Hope you like it. Richard.
  24. 61 points
    I never seem to be pleased with my editing of the M45-data I´ve got but now I think I´m getting there! This time I pushed the faint nebulosity even harder but still managed to keep it together... sort of. I could have sharpened the nebulosity more but I like the dusty, fluffy look. This is a bit over 15,5 hours of data, captured using Canon EOS 1100D and a Canon EF 300/4L IS lens. My mount is a HEQ5 Pro Synscan, guided. 31*3 minutes 87*5 minutes 55*8 minutes All at ISO 800. I hope you like it, don´t think I will do much more reprocessing of this one now. No use beating a dead horse
  25. 60 points
    I have had this on the PC since January and have refrained from posting it as I really can't decide how I feel. It started off as a more usual colour palette for me, but it always seemed very flat. I went back to process and decided to leave the green in and see what that bought to the party. It certainly seemed to give it a more 3D feel and more general depth..... but it has been tweaked here and there now for months. It hasn't been posted anywhere yet as I think it's too far from my comfort zone colours to be able to decide how I feel about. I've tried to look at it objectively and wonder what I'd say if someone else posted it, and I can't quite decide whether I'd give it a 'thumbs up' or a 'thumbs down' I've thrown it open to comments and criticism here - Please feel free to be as brutal as you like...... I need to hear it Details: Mount: Mesu 200 Scope: Takahashi FSQ85 0.73x Camera: QSI683 and Moravian G2-8300 This has been data from last year and this year. 27x1800s Ha 11x1800s OIII 20x1800s SII Totalling 29 hours of integration. I can't link to a high res version as there isn't one online!
  26. 59 points
    Some photos added today?.. Mint Takahashi FS128 on Tak EM2 mount. My heartfelt thanks to Tony for waiting for so long until I could proceed with the purchase, and to my wonderful wife Heather for her loving support. Can't quite believe it.. Dave
  27. 58 points
    These are a few considerations that I've found handy and might be useful with organising your observing . Practical. Red torch, check it's working and the batteries are ok Check your finder is aligned with your scope. Half covering a Telrad will enable you to align on a distant chimney in the day. Notebook or paper and a soft pencil, 4B or softer. This'll avoid ripping into paper as you note or draw in your fever of excitement. A cardboard box on it's side will keep stuff out of the dew. Ensure your dew heater is on straight away , they take time to get results. Have a hairdryer handy in case. Ensure that if you do leap of bed that you can lay your hands on, Glasses. Clothes. Shoes. Ensure the bloke in the living room mirror doesn't leap out at you.shocking. Keys to the door. White spray paint the edge of garden steps.ouch. Ensure the washing line pole is out of the way.Ouch. Planning. Before starting , the session will be productive if you have a list of targets or you could end up looking at the same old familiar suspects. Check out which constellations are favourably placed for you. Go one constellation at a time. You'll find one leads to another.Get the targets noted down , a photocopy of the relevant star chart with these marked out helps. Initially I use a clipboard. A garden chair(s) or table is ideal for putting gear on within reach. An A4 plastic sheeted file will keep these safe. One idea is to start off with the Telrad Messier charts. http://www.atmob.org/library/member/skymaps_jsmall.htmlThese are quite plain and can easily be added to with the best of targets. Your own charts will be personal to you, not packed with stars, but easy enough to star hop with. Remember that if you do take books and charts out, they are dew magnets particularly in autumn and spring. Best scanning them or making a rough reference. Results ! A few notes of magnification used and noting which are the best targets is worth keeping,addition to a brief description, I grade clusters with asterisks, four being the best , with compact star clouds or simple spectacular such as NGC 2301 or NGC 7789. Any additional notes such as dust lanes or core brightness of galaxy will be of interest when you do an observing report. Any reports however brief are really appreciated. Simple drawings of planets will give you great pleasure and show you the changes in details . There is so much of interest and a quick net search later will reveal the background of what you have found. There is a certain excitement knowing how far away NGC 2419,"The InterGalactic Wanderer "is and observing the oldest globular clusters and the newest planetary nebulae. There is no harm in adding a few faint targets , some of the galaxy magnitudes don't take account of bright cores. Being on the edge of town my lists go down to about +11, with some extras for dark skies! Forum observing reports are one source of targets, they are things that other observers actually see. You can also fill your individual constellation lists with monthly magazine suggestions and books. Apps and Stellarium are a rich source, just get them down on paper ! When I started , I borrowed library books and went through the constellations. This will give you a wide range to look at. If you wish to spend a night just on planetary nebulae for instance, your constellation info will provide you with an observing list. Keep these lists, noting not only those seen ,but the ones you had trouble with. Other observers can help, just let them know ! If planets are up, ensure that you know where to look. Once you are used to the night sky, you'll soon spot any wanderers along the ecliptic. Just as relaxing is sitting out there looking or using small bins. An evening with a simple Dob and the sky and you'll soon drift away. It is wonderful out there under the stars, a bit of planning and you'll be looking forward to your next session under those elusive, Clear skies ! Nick.
  28. 58 points
    Well, I didn't think I'd be making this post but here it is - tonight I have managed to see the Horsehead Nebula, Barnard 33 The sky here tonight is the best and darkest I've experienced for a long, long time. The transparency is excellent although the actual seeing is mediocre in terms of star images, splitting doubles etc. M31 is a direct vision naked eye object and notably extended too. The double clusters in Perseus are clear without any sort of optical aid as is M35 in Gemini and the brighter 3 star clusters in Auriga. I don't know what the naked eye limit at the zenith is - probably close to mag 6 ? This is as good as it gets from my back yard. By 12:30 Orion was well above the rooftops and the streetlights have gone out. Neighbours have gone to bed and there are no lights on in our house or any in the vicinity. It's all "come together" for a change and my 12" dob is definitely the right instrument for these conditions. I've been trying to see the Horsehead Nebula for a few years now. I've got to know the star field around the star Alnitak (lowest of the "belt" stars) well and I've read the advice pages on the target plus reports from those who have seen it many times. All lights off. Laptop screen is dimmed, curtains are closed tight. I spend 20 minutes outside just looking around the sky, getting as fully dark adapted as I can. First stop on the path to the Horsehead is NGC 2024, the Flame Nebula, which is right next door to Alnitak. Good start tonight - the Flame Nebula was not only visible without a filter, but the dark rifts that run through it, like the branches of a tree, were also visible. Even the dazzling Alnitak in the same field of view could not drown out the illuminated lobes of the Flame. Ok, time to add the Astronomik H-Beta filter to the eyepiece of choice for this search, the 24mm Panoptic. Filter in place, I was pleased to see that the Flame Nebula,it's shape and form were still quite visible. Time to push Alnitak and the Flame out of the field of view and to concentrate on the 1 degree of sky that is home to the Horsehead Nebula. There are 3 stars that frame this patch of sky on one side, one of which is bathed in faint nebulosity which this evening was visible with and without the filter. This is NGC 2023, a faint emission and reflection nebula. I had seen this before but not as clearly as it was showing tonight. Another hopeful sign. Now the big challenge. I knew that the key to seeing the Horsehead Nebula was to detect the faint glow of the emission nebula IC 434 but in previous attempts this was the fence that I'd fallen at (Horsehead - get it ??!! ). Tonight though, as my eye adjusted to the filtered light across the field of view, the elongated but rather amorphous band of slight cloudiness that is IC 434 gradually became apparent, varying in density here and there, almost not there sometimes but re-confirmed subtly over and over as my eye swept around the field of view. And there it was. A bay, an intrusion, a dark overlay, a piece of IC 434 was missing !. Quite a large piece as well or so it seemed as my eye moved from one side of the field to the other bringing various degrees of averted vision into play. It's been described as a dark thumbprint and I'd concur with that. Not a chesspiece, no snout or ears, but a soft edged, ill defined shark bite chunked out of the side of the nebulosity, leaving the black sky to spill into that cove and the nebulosity of IC 434 to curve around it. One side of where the dark intrusion started was marked with a very faint pair of stars which I believe I've read Swampthing / Steve describe as his indicator of the Horsehead location. I kept observing for 20-30 minutes trying all the tricks I know to keep all stray light from around my eye and the eyepiece. The clarity of what I was seeing ebbed and flowed, possibly after a while because my eye was just trying so hard !. But the more I observed, the more confident I became that I was seeing this long sought target. Ok, it was very indistinct - well I'd thought it would be, especially if I ever managed to see it from my back yard, but I was pretty sure that I was looking at Barnard 33, at last !. I rather reluctantly dragged myself away from the eyepiece and tried a couple of other eyepieces with the H-Beta filter attached - a 30mm plossl (Vixen) and the 17.3mm Delos. Each time I came back to the eyepiece I needed 10-15 minutes to get back "into the zone" again. But the same pattern of vague nebulosity was indeed replicated with the darkened bay pushing into the cloudy edge of IC 434 in the same place, to the same extent and at the same angle, each time. The original 24mm eyepiece seemed to provide the most distinct view but I should really say the least indistinct !. Not a spectacular view at all, just suble variations of dark and slightly darker patches of space peppered with stars. Without the filter the stars brightened but only the Flame and NGC 2023 were visible in terms of nebulosity. IC 434 and the large, dark, thumb shaped indentation were nowhere to be seen. OK. Back inside to warm up (it's cold out there despite the adrenalin flow that the hunt has prompted). Take stock of what has been observed. I turn to one of my favourite web references on deep sky observing - Jeremy Perez and his wonderful "Belt of Venus" website. Here is what Jeremy says about his observations of this target, albeit with a smaller aperture scope than mine (from a darker sky though, I'll bet !): http://www.perezmedia.net/beltofvenus/archives/000379.html Re-reading the above has confirmed 100% for me that, tonight, I have seen the Horsehead Nebula So much of what Jeremy describes chimes with my experiences and my impressions tonight I got into astronomy 40+ years back with the help of Sir Patrick Moore's "The Observers Book of Astronomy" and in that little volume there is a greyscale long exposure image of the Horsehead Nebula which made a big impression on me then and has stuck with me to this day. Quite possibly this is the least impressive target I've seen though a scope in all those years observing but the pleasure that seeing it at last has delivered is very tangible indeed. If you have got this far, thanks for bearing with my rambling descriptions
  29. 57 points
    Imaged with my AG12 and H35. A massive task to tame Alnitak, it took over 12hours to process this one. Exposure times were 4x900s in H-alpha, 4x900s in Red, 4x820s in Blue and 4x640s in Green. Processed in Photoshop and Lightroom. Comments welcome thanks for looking
  30. 54 points
    Hi everyone Today I woud like show You my longest expose photo. This is very well known OU4 (Outters4) Gigant Squid Nebula. In polish wheader condition I started cathing it at last week od may and finish few days ago. All frames without moon. It is O3RGB composition. QHY695A, Ioptron Cem60EC, TS APO100Q, Chroma O3 3nm, Chroma RGB. O3 47h @1200s, RGB 3h @300s link to full size https://www.astrobin.com/7wcspr/ edit. Sorry, I forgot Negative and starless version full at Astrobin
  31. 54 points
    Headed out after work last night in chance of capturing the arch for the last time before summer nights really take a grip. I had a idea of a location and it worked out better than planned. theres a slight glow to the north ( left of the image) as the auroa kicked off at 1:30am sadly the mountain was in my way but i like the purple hue's. Sony a7rii Tokina F2 FIRIN lens 21x12" iso 6400
  32. 54 points
    Two panels, the lower one from last year. The top one was from this week, with guests, but Tom remembered that he also had a good dose of Shark Nebula data so that went in as well. The lower panel is Ha OIII LRGB for the supernova remnant and planetary nebula while the top is only LRGB. About 50 hours, dual Tak FSQ106N/Atik 11000/SXVH36/Mesu 2000. This time I went for an honest colour, resisting the temptation to try to make the Shark look like an emission nebula! The three VDB objects are, 149, 150 and 152. The PN is G111.0+11.6 (catchy name) and the SNR is ... I've forgotten!!! Olly, Tom and guests.
  33. 53 points
    This Sunday 24th May at 8pm, we are launching the first of an ongoing series of virtual astronomy talks, workshops and presentations at 'StarGaZine'. You can attend StarGaZine events free of charge via the Zoom video communications platform. For our very first event (Sunday 8pm) Steve Richards / @steppenwolf will provide his talk 'Making Every Photon Count: An Introduction to Deep Sky Imaging for Observers'. His beginner-friendly talk will explain the equipment and techniques necessary to successfully capture deep sky targets. After the talk there will be a Q&A session. The following week (Sunday 31st May) Nik Szymanek will provide a talk followed by a Q&A session. After that, we are working on a week long imaging conference with a speaker every night covering specific topics. Dates, speakers and topics will be announced later. Initially the talks focus on astrophotography but, ongoing, we will cover a wide range of astronomy subjects. Why are we launching StarGaZine when we already have StarGazersLounge? There are several reasons but primarily it is because: During the pandemic we cannot have a SGL Star Party. Many regular astronomy society meets are also not happening. The usual astronomy fairs and shows are cancelled. It will compliment and enhance SGL. It will promote astronomy to a wider audience. It will be fun @daz has agreed to be host. @Grant will cover the techy stuff and some general organisation. Ian King will help us find and book speakers. @FLO will cover the costs (i.e. speaker fees, Zoom license, equipment required, etc). If you have suggestions or know someone who might be interested in providing a talk, workshop or presentation, please let us know. As I type this Grant is hosting an outreach event, via Zoom, using the Ikarus Ovservatory setup at Pixel Skies in Castilléjar, Spain. But he'll be along later to explain how to find and access StarGaZine events. We hope you will join us
  34. 53 points
    Made this false colour venus image using a UV data from 9th April and IR data from the 10th April (as I didn't capture any IR on the 9th). As the IR channel is generally featureless I didnt see any issue doing this, just needed to align and resize the IR slightly to match. 90k frames of UV and same IR. 20% stacked for each and synthetic green made from a 50/50 mix. Fullerscope 8.75" newt with APM 2.7x barlow. Altair GPCAM 290m with Baader UV and ZWO 850nm filters. Image resized 200%. North up.
  35. 53 points
    Here are my attempts at Astrophotography with a smartphone. Taken thought a 10 and 20inch Dobsonians. Most of the photos have been processed through photoshop. The eclipse photos where taken with a smartphone with a small screw on Samsung lens and a home made white light filter. I have more on my Instagram https://www.instagram.com/astroramblerphotos/ Venus Messier 13 (Hercules Cluster)
  36. 52 points
    What a fabulous night it was last night (Saturday 6th Oct) Everything worked flawlessly with no issues except for one green channel getting trashed from high cloud, that passed pretty quickly and I was able to continue. This shot is a simple RGB image, I do have plans to get some more data including Luminance and Ha to enhance the H2 regions. Im quite please with the core detail. Exposure time 7x 900s in Red, 7x640s in Green and 860s in Blue. Taken with my AG12 and H35 camera Click to view full res image Thanks Peter Shah RGB Managed to get 4hours of Ha 900s subs....click for full res version RGB and H-alpha
  37. 52 points
    Naturally this is a popular target with guests, which means I can accumulate data and combine it to keep chipping away at the quality of the final image. Last night we ran the dual Tak rig on this for our guests' new image, but I also combined it with everything I already had from both the Taks and the TEC140. It allowed me, above all, to push the outlying dusty structures without the need for noise reduction. I've lost track of the total exposure time but it will be around 25 to 30 hours. I thought I was approaching the limit of useful data last time I worked on this but the extra 9 hours from last night really did make a difference. This is LRGB, mostly from the dual Tak FSQ106 rig but wth TEC140 data thrown in. Mount, Mesu 200, cameras Atik 11000 mono. Click on it for a larger version. Best wishes, Olly
  38. 52 points
    Following on from my Horsehead nebula in mono thread here I was quite happy with it as it was.... then ..... @pietervdv was a very naughty boy and suggested that perhaps I *may* like to do another pane above it. Well how could I resist when I was finally up and running with the dual rig. Double bubble on the Ha time as I've got a 3nm Astrodon in both camera's. It would have been rude to ignore his suggestion! The original thread was called widefield.... so this one can only be *even wider* All comments and thoughts welcomed (except those that suggest ANOTHER couple of panes are in order) - There will be no colour either this year Details: M: Mesu 200 T: Takahashi FSQ85 0.73x Pane 1: C: QSI683 3nm Ha filter - 27x1800s Pane 2: C: QSI683 3nm Ha filter / Moravian G2-8300 3nm Ha Filter 20x1800s QSI / 8x1800s G2-3800 Total exposure time 27.5 hours You can see a larger version on my website here
  39. 52 points
    Snowdon and the Milky way panorama. 41 images captured on a Sony A7S and Samyang 24mm f/1.4 lens exposed at 8 seconds, f/2.0 iso5000 and post processed in Autopano Giga to produce the stitched image and then processed in Autopano Panotour to produce a 360 interactive panorama which is quite nice to play with full screen
  40. 51 points
    I'm still dizzy after processing this one for each LRGB filter. Comet 21P meets open cluster M37 in the night/morning of 10/11 September, at perihelion. This is a combination of 60s x 30 x 4 subs, taken through the SW130PDS with an ASI1600MMC. https://www.astrobin.com/366252/ No deconvolution applied, only noise reduction. About the remaining noise?! ... yes, please. Unfortunately the light pollution at home didn't let me record more. Thanks for watching and clear skies! Alex
  41. 51 points
    Hello Sometimes show images at 100% does not allow to see all the details. If you are looking the smallest craters visible it is necessary to enlarge the image. Here are somes pictures, Copernicus at 300%, Copernicus at 120%, a part of Clavius at 120%, Atlas at 300% and Walter's area at 150%. Of course click on images for full resolution. Regards. Luc
  42. 50 points
    This is 3.5 hours of data with the RASA 8 and ASI2600MC (105 x 2 min at gain 100, -10°C) on a NEQ6. There is apparently quite a bit of dust around M45 that I have not noticed before. I am pleased to see how deep this telescope/camera combination can go in a few hours. A dark site (Bortle 2-3) helps of course. Stacked in PI and mainly processed in PS, as usual. EDIT: I now added a second version of the image, inspired by Olly's reprocessing of his data, where I have sharpened the image more (mainly HiPass filtering and LCE in PS), getting closer to the limit of what the data can support.
  43. 50 points
    I started this back in February 2019 and finished it over the last three beautifully clear nights capturing whilst I slept. In total 13hrs of Lum, 5 hrs each RGB and 14hrs of Ha. Lum and RGB through my Esprit150/SX46 and Ha through piggybacked Esprit100/ASI1600mm mounted on a Mesu 200. Processed in APP, Pixinsight and Photoshop with mild deconvolution of Lum and Ha. The Whirlpool Galaxy, also known as Messier 51a, M51a, and NGC 5194, is an interacting grand-design spiral galaxy with a Seyfert 2 active galactic nucleus. It lies in the constellation Canes Venatici, and was the first galaxy to be classified as a spiral galaxy. Distance is estimated to be 23 million light-years and diameter 76,000 light years. Its mass is estimated to be 160 billion solar masses What later became known as the Whirlpool Galaxy was discovered on October 13, 1773, by Charles Messier while hunting for objects that could confuse comet hunters, and was designated in Messier's catalogue as M51. Its companion galaxy, NGC 5195, was discovered in 1781 by Pierre Méchain. In 1845, William Parsons, 3rd Earl of Rosse, employing a 72-inch (1.8 m) reflecting telescope at Birr Castle, Ireland, found the Whirlpool possessed a spiral structure, the first "nebula" to be known to have one. Also in the image are IC4263 (top right) , IC4277 (below left) and IC4278 (below) Thanks for looking Dave
  44. 50 points
    Hi SGL, I ve been away for quite a while, but its good to be back, and have a picture to post. This is Cassiopeia, a 25 pane 530mm mosaic. I started this in 2016 when I captured the Lum panels, it took building my own remote observatory at Ollys in France before I could capture the RGB, Ha and O3 data. This comes to about 350hrs of LHaRGB data about 240 of those taken in the last year remotely. No noise reduction has been used, and only sharpening on a few certain objects. I re-took about 5 panels in RGB due to stitching and gradient issues. There are a lot of objects in here that I have not seen before. mostly Sharpless objects, but the main defining nebula here is the "Breaking Wave" that Olly coined when we went deep in Ha in this area before. I was pleased to find the "Face On mars" as I like to call it SH2-173 in the mix, along with numerous other objects. I m attaching a small image, and then a bigger attenuated version which I hope you can zoom in to. My friend is setting up the Zoomify option on the website but it may take a few days, so I ve decided to post these in the meantime. I hope you like it, and of course huge thanks to Olly Penrice, Steve Richards for helping with the remote set up, and all the others on the group who helped me trouble shoot the observatory issues. Tom.
  45. 50 points
    TS130 f6.6 G3-16300 Riccardi APO Reducer und Korrektor 0,75x SkyEye Observatory 70x300 L 40x300 R 40x300 G 40x300 B
  46. 50 points
    Recently I bought a Canon 6D for daytime photography. Of course I was going to put it one day behind a telescope. Said and done. Last weekend I went to my girlfriend's parents' village (Clear Outside estimates an SQM of 21.9 there), I put the Canon 6D behind the Esprit 80 and both of them on top of the tuned AZ-EQ5. Guiding was done with a finder guider and overall stayed at 1.5"-1.8" RMS. But the 6D has large pixels and I also downsampled the final image so there shouldn't be much loss due to poor tracking. Moon was rising just before 11 so I started early, shooting Orion as the first panel. 2 other higher panels followed, consisting of 21, 21 and 19 subs, 5 mins exposures at ISO1600. For the Orion's core I used also 12x5s. That's a total of 3 hours. The stars towards the corners are not perfect with the Esprit80 and a full frame sensor, but resampling at 60%, I do not notice any weird shapes. Can't wait to shoot a wide Antares region with this setup. On astrobin: https://www.astrobin.com/393580/ Clear skies! Alex
  47. 50 points
    Well no surprise this was coming next after the M81 and M82 recently published (total 103 hours data from RCOS, AP RH and OS RH - the latter used as the base frame onto which the objects were placed) - think this concludes my look at this area. C&C welcomed, if not hope you like.
  48. 49 points
    We will soon apply a significant update to the SGL platform but before we do we want to remind everyone what SGL is, and is not. This is important because it underpins the way SGL is constructed and moderated. What is SGL? SGL is a positive, safe, friendly online community where you can discuss all things astronomy with like-minded people. Whether you are beginner or professional, visual astronomer or astrophotographer, armchair astronomer or cosmologist. SGL is for you. SGL is not Facebook. SGL does not amplify negative emotion, does not insert dodgy video into your timeline and does not lock you in. There are no fake members or bots. No fake news or click-bait. You are not wrapped in a filter bubble then sold to advertisers (our sponsor pays the bills). At SGL your worth is not determined by how many followers or 'likes' you have. So if you enjoy drama, dissent and controversy. If you enjoy discussing politics and social injustice. If you enjoy constructing carefully worded insults. If you like sharing photos of your cat or breakfast. SGL will not suit you. SGL does however have a Lounge area for non-astro discussion. This is separate and distinct from the astronomy boards. Please help us keep it this way. Best wishes, SGL ADMIN & Moderators
  49. 49 points
    Hi, It's been a long time since the last time I posted anything here. I was mostly into deep sky shots back then but planetary imaging has taken over. I've been making mirrors and scopes over the last two years with a goal of making a good big planetary scope ready for Mars in 2018. That scope may end up being my current 20" f3.8 tracking dob or it could be a 25" or 30" version if get around to it. For now the 20" is doing well. So here's a few shots. equipment: 20" f3.8 traking dob, ASI224MC camera, ZWO ADC, 5 x powermate. 5/2/2017 Derotated Jupiter by Raymond Collecutt, on Flickr 3/3/2017 Jupiter 2017-03-03-1337 by Raymond Collecutt, on Flickr
  50. 49 points
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