nebulae - what can I see with an 8 inch dob?

[banner001]

seeing is mainly affected by moisture content in the sky.

unfortunatly as i dont know where you are i will assume you are in the UK, so here its usually poor seeing as the atmosphere is quite moisture-laden, aircraft do dump some water into the atmosphere, their most anoying aspect is that they can condense water into small droplets = clouds, it has been shown in several studies that the presence of aircraft leads to more clouds.

and again, if you have bad light pollution that will kill off any views you want to get, there is no way around LP, no amount of filters will ever get rid of it, you need to deal with it and accept poor quality skies, or try to get to a darker site, preferably at a slightly higher elevation, even a few hundred meters will make the world of difference.

[coffee_prince]

using the bortle scale, bristol is 8/9, so pretty terrible.

need-less light pollution

this seems accurate as it also shows my area is an airplane route

is this enoughto be a reason why i cant see any faint fuzzies?

[pete_l]

My suburban sky used to have a limiting magnitude of about 3.5. Now that the council have fixed the streetlights, it's better: about 4.5. I can see the two 4.5 Mag stars near Vega - which is pretty much directly overhead these nights. Howver, as soon as I stray far from the zenith, the LP still puts severe limitations on what I can see. By about 30° above the horizon, to the south (the only direction I can get that low) my VLM is still about 2.

In those "bad old days" sorry: nights, I could just about see Andromeda as a faint fuzzy blob through my 8-inch SCT. It was a massive anticlimax and really, not worth ever going back to. I could also see M42 when the local football club decided they weren't going to obscure the whole sky with their floodlights when they wanted a practice (which they sorely needed , but that wasn't any consolation). The basic problem was partly the sky brightness, but also that my eyes never got sufficiently dark-adapted to see stuff through the eyepiece. I know there are techniques: such as a towel over the observing end of the telescope, or an eye-patch, that may improve the situation but they're not really practical solutions.

Apart from those two I was limited to stars, doubles, planets and clusters. The only way I could see things that weren't point-sources (or for the planets: close to point sources) was with photography.

So to answer the original question. Under light-polluted skies, I reckon M31 and M42 are your best targets. I never had any success eyeballing any other nebulae.

[umadog]

Anyone who says that light pollution filters are of questionable use visually, doesn't know what they're talking about. Complete rubbish. I was out last night and saw the N. America nebula, the east and west veil, pickering's wisp, and the cresent nebula. None of those were visible without a filter and all popped nicely into view with a filter.

Aircraft won't create bad seeing (turbulence). That is caused by atmospheric heat currents and the jet stream. It's also cause by your primary mirror not being cooled to with in a degree or two of ambient. That latter, of course, you can control. Poor seeing won't affect your ability to find DSOs, however.

I still don't think there's anything wrong with your scope. Nothing you have said indicates that something is wrong with it. For example, you haven't complained of focus issues or bad star images. Even if you had a minor problem, you'd likely still be able to find DSOs. It's more likely, IMO, that you aren't looking in the right place or that you're looking for targets which are being overwhelmed by light pollution. There have been many times when I couldn't find an object and thought it was too faint for the conditions only to later find that I was looking in the wrong place. I was certain at the time that I was looking in the right place. This is more likely to happen in light polluted conditions where few stars are visible. My best advice is that you track down your local astro club and get them to show you the ropes. The coming weekend is a new moon. Any club worth their salt will be out viewing. Honestly, I'm not 90% certain that the problem is light pollution an inexperience. Buy a Telrad.

[coffee_prince]

I also think my scope is fine, but I think as explained by others, the light pollution severely limits what I can see. This would explain why I can find star clusters and stars, but I am also willing to accept I may be missing things, but I find it hard to believe that I am missing certain messier objects that are near the big stars, i don't think you can go too far off course, especially with a wixey and compass to hand. I've also been scanning the sky in a methodic fashion, once I get the altitude and azimuth pretty much spot on, I look around carefully but find nothing.

I'm going to buy a telrad, it should help tell me where I am going, and I do need some help but the club in my city do viewings outside of the city, so I can't get there.

[Squif]

I say its light polution - I live in the town and my telescope was pritty limited (I kept wishing for a powercut ) however went out to the country and the view was amazing! the telescope was like a different tool. I thought mine was broken when I first used my telescope so I would take it out somewhere less yucky and give it a real go!

[swamp thing]

but the club in my city do viewings outside of the city, so I can't get there.

You could contact them and ask of the availability of some transport, I'm sure one of them would be able to squeeze you and your scope in if you were to contribute some gas money.

Most amateurs are a friendly bunch only to willing to help others out.

Regards Steve

[umadog]

+1 on contacting the club. From areas that are severely light polluted, astronomy is rather restricted. From a darker site things are a totally different ball-game.

[banner001]

I was out last night and saw the N. America nebula, the east and west veil, pickering's wisp, and the cresent nebula. None of those were visible without a filter and all popped nicely into view with a filter.

thats true for nebulae...they emit different wavelengths of light to stars, but pop one in and it will diminish the light from galaxies, it diminishes them from point sources of starlight, galaxies are 99.999% stars so they will apear darker, for nebula you can buy filters, for galaxies all you can really do is go someplace darker.

[umadog]

Sure. I know you understand this, banner, but some beginners might be confused by your use of the word "different." To clarify the key concept: Emission nebulae emit light in narrow bands of the EM spectrum and stars also emit at these same bands. However, stars emit in a whole load of other bands as well: a huge range of the EM spectrum, in fact.

LP filters work because we can choose to pass nebula emission lines, such as OIII, whilst discarding virtually everything else. This improves contrast between the DSO and the sky background. Contrast improves visibility. Stars are broad-band emitters, as is a lot of light pollution. Consequently, the spectra of light pollution and starlight overlap too much for a useful filter to be created. For that reason, LP filters work poorly on galaxies. They also work poorly on reflection nebulae which shine by reflected starlight. The fact that stars are point-sources does not impact whether a useful filter can be created.

[umadog]

seeing is mainly affected by moisture content in the sky.

I think you mean "transparency", which is indeed affected by moisture. "Seeing" refers to the degree to which the image is distorted by atmospheric turbulence, which itself is driven by temperature gradients. The distinction is important because it's not uncommon for good seeing to go hand-in-hand with poor transparency. Some of the best seeing occurs on still nights, where the lack of air-motion causes haze to build up. The conditions might look awful for astronomy, but in fact the still air produces good seeing which makes it awesome for planetary and lunar observing. A friend of mine recently got his 8" Dob to 400x on Jupiter under such conditions. Usually around here we're lucky to hit 280x. Well worth knowing...

[coffee_prince]

Best night i've had in a long time, the skies were pretty cear and dark. managed to find the orion nebulae it looks a lot better with averted gaze, for some reason the wixey and stellarium were giving me wrong coordinates, I used the "new" telrad instead and found it. Why was this? The wixey and stellarium coordinates were fine for jupiter...

Pleiades looked great but I need a wider ep as the 25mm culd not fit it all in, is a wider FOV better or a low mag piece?

I think I found neptune and uranus, but can't be sure because they are supposed4 to look green or blue?

I tried my new neodymium filter on jupiter, it made the colour bands easier to discern.

But I am having problems finding things high in the sky, near the horizon its a lot easier, the higher up you go the more confused I get. I could not find the andromeda galaxy. I can see on stellarium its near cassopiea so i tried to hop frm that but failed.

[banner001]

for andromeda i try to locate it in the finderscope first.

also if you are having real dificulty you can always "cheat" a little, and by cheat i mean either add compass markings to your dob base, buy a wixey angle finder, or like me do both

that way if i find something on stellarium i can manually slew myself to the correct degree in alt/az, and its always within the finderscope, i just need to do a slight adjustment to see it in the eyepiece.

getting a wixey is easy, marking out precise angle markings (i do mine at 5 degree intervals) is harder.

even with a wixey you can star hop to the approximate location, set the correct angle of declanation and then you need to be quick, but it should only need an AZ slew to find your target, again andromeda is really quite faint, it has quite low surface brightness because it is so massive, try to find it in the finderscope first is my suggestion.

[brantuk]

You can get the setting circles in a pdf file here:

Sky-Watcher SkyLiner 200 Dobsonian Telescope

Take the disk into somewhere like Staples office supplies and they'll print it out at the correct size for your dob base diameter on acetate film that can be stuck on. Costs about £10-£15. Then all you have to do is make the hole/pointer. Here's a nicely done soltuion:

http://www.homebuiltastronomy.com/Ma...ingCircles.htm

[banner001]

i used the POWER OF GEOMETRY to work out my angles

find the chord length necessary to generate 5 degree increments and did that, im out by 1 degree overall...but whats one degree when the finderscope shows me a FOV of 4 degrees...im still always on target.

DSC would be nice, but mine cost me exactly £0.00...well maybe a small amount of electricity to power the PC, and i suppose i used a small amount of pencil lead and permanant marker ink...

[twotter]

Pleiades looked great but I need a wider ep as the 25mm culd not fit it all in, is a wider FOV better or a low mag piece?

I found the same thing with the supplied 25mm EP, so I bought a 32mm GSO plossl which allowed me to view Pleiades nicely. But, then I read something about wider FOV EPs along the lines of shorter focal lengths giving more magnification but with the bonus of 'blacker' night sky and better contrast - IYKWIM?

Anyway, I'm replacing my 32mm plossl (FOV 52 degrees) with a 24mm Hyperion (FOV 68 degrees)

[umadog]

My hunch with the Wixey is that you'll find it useful at first whilst you're learning the general locations of stuff in the sky. However, once you've learned that stuff you may well never use the Wixey again. You'll be faster simply star-hopping with the Telrad. More accurate too, probably. So don't get overly concerned if the Wixey approach isn't getting you there every time. The point is just to find stuff, doesn't matter how you do it. Wixey, GoTo, DSC, star hopping, etc.

Star hopping is good because there's no technology to go wrong. Personally, I prefer to star hop than de-bug equipment. Every time I learn how to reach a new object, I have something extra in the bag. It's all useful extra experience. I used to have an Orion COL and basically never used it because it didn't always work. I didn't see the point in spending my time de-bugging the device when I could have just used that time to find the object. Time under the stars in precious.

[brantuk]

"i used the POWER OF GEOMETRY to work out my angles"

That's great Banner - no probs with that at all and cudos to ya. It was just an idea for folks who don't have time/inclination for geometry. But whatever method you choose is cool

[coffee_prince]

Managed to find the Wild Duck Cluster and Andromeda, I'm getting somewhere now!

I am reading online that some people can use higher magnifications so it fills the whole EP, I guess I have bad light pollution, but both messiers appeared simlar in brightness, needing averted gaze to really see it better

[banner001]

Managed to find the Wild Duck Cluster and Andromeda, I'm getting somewhere now!

I am reading online that some people can use higher magnifications so it fills the whole EP, I guess I have bad light pollution, but both messiers appeared simlar in brightness, needing averted gaze to really see it better

for big things like the andromeda you need to use the "surface brightness", not the mag, wild duck cluster is surface brightness ~12, andromeda ~13...so thats about right, remember that even though the andromeda galaxy magnitude is listed as ~3 thats spread out over the whole galaxy...so a low surface brightness.

i would guess that a lower mag EP would show you it better, more concentrated light in a smaller area? thats usually the case, dim things look brighter at lower magnification...

[coffee_prince]

last night i could not find the triangulum galaxy, try as I might, and any messier clusters i found looked not so good due to the poor conditions. jupiter looked a lot better tonight with crisp bands, which ive never noticed before. but seeing conditions for everything else was poor

i'm not sure if the neodymium makes any real difference in light pollution reduction, but i kept it in the ep for the sake of it.

it boggles the mind to think you can see andromeda in perfect skies with the naked eye, damn light pollution

[Stu]

Coffee_prince, you can indeed, it's well worth a trip to a dark site. I was down in Dorset recently and the skies to the south were amazing. Andromeda was very obvious to the naked eye, and looked bigger than I have seen before. The milky way was so bright it looked liked high cloud!

Managed to see the brighter part of the Veil nebula (eastern veil?) With a 4" apo, 31t4 nagler and OIII filter.

Cheers

Stu

Sent from my GT-I9000 using Tapatalk

[coffee_prince]

Despite a near full moon out tonight I managed to find for the first time a few messiers. I think if you expect not to find stuff you don't tend to do so well, but now I realise even in these poor skies I can find several things in the sky to enjoy.

m57 ring nebuae

m13 cluster in hercules

m92

They were all pretty hazy, ring nebulae definitely most interesting, despite fuzziness

Getting the hang of starhopping.

I should start making a checklist, but this thread is just a notepad for me right now...

[coffee_prince]

New items found m15, m2 and the Dumbell m27

Could not find m101 tonight, despite clearest night in a long time

[Stu]

I tend to stick to the 'brighter', smaller dso's when looking under light polluted skies. Mine actually aren't too bad, but still find it pretty difficult to see galaxies because the light is spread over such a large area. I've never managed to spot M101 from here.

There are plenty of globulars to see, which I love looking at, and things like m27 and 57. Probably best will be m42 when it returns in the winter, so much to see in that at different magnifications.

I'm starting to do more on double stars, and also the moon which I regularly look at, but have never really ' learnt' the features of.

Skies are at least getting a bit darker now :-)

Stu

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