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Rob Sellent

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Rob Sellent last won the day on November 14 2019

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About Rob Sellent

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  1. Judging by all the threads you've set up this week, I imagine you're rooting for some cosmic phenomenon that will indicate dooms day for Earth. To wet your appetite, have a gander at the life cycle of stars like the Sun or else massive asteroid impact.
  2. A megaparsec is a million parsecs (mega is a prefix meaning million; think of megabyte, or megapixel) and as there are about 3.3 light-years to a parsec, just one megaparsec is quite some distance. Now multiply that megaparsec by 900, 3,000, or what have you.......
  3. In a sense, to view the Sun in H-alpha I feel the question is to either go for a Quark eyepiece or a dedicated H-alpha telescope and to be honest I don't feel there is a correct answer. In general, one important feature in astronomy is aperture and this also applies to solar viewing in white light and H-alpha. Looking just at the Lunt scope (50mm & 60mm) one will find that they are beautifully designed H-alpha fracs and work exceptionally well. They have the advantage of being solely dedicated to H-alpha, need no time to be up and running (great for 'grab and go') and with something like the 60mm, you will be able to see all the possible solar features that are in H-alpha. I no longer own a Quark but evidently it is not a telescope but rather a type of eyepiece. You need an external battery and cable to run it and you need a refractor with a focal length between f6 to f8. Most people with a Quark use a frac with ED or APO quality glass. To this you may want to add a UV/IR cut filter and if you use a refractor with more than 100mm aperture you will have to buy a D-erf. After 'faffing' - if you pardon the term - the Quark will give you significantly more aperture than the Lunt 50mm or 60mm and that should translate into a more detailed view. You can put the Quark into something like an 80mm ED frac and you'll have a telescope in h-alpha running at 80mm. That kind of thing in Lunt terms would costs you thousands! However, the Quark is not perfect. It has a 4.3x barlow in it, so you need a relatively short focal frac (f6 to f8 is ideal) to keep the magnification down. Also, accounting for Barlow, depending on the focal length of your scope, you will not have a complete image of the sun. By way of example, if you take an 80mm frac and a Quark, you will have 80mm of h-alpha aperture but with the scope's focal length of 600mm and 4.3x Barlow in the Quark, you'll have a focal length of 2580mm. With something like the 32mm Plossl you will have a working magnification of 80x. Thus, the Quark is too often dependent on atmospheric conditions. What I mean by this is that on average one is generally only working around 50x both in white light and h-alpha. There is also the question of exit pupil. If your telescope has a focal ratio of say, f7.5 and the Quark has a 4.3x Barlow, you'll have a f32 scope. With the 32mm Plossl, you'll end up with an exit pupil of 1mm. Some folk may not find this too comfortable either. This is certainly not making it difficult for the Quark but I feel these points are worth raising. So again, we return to potential possibilities: Quark + Refractor + Battery + Cables + UV / IR cut + TeleVue Plossl 32mm, more faff setting up, not much play in magnification range, perhpas not always a full disc, possibly dependent on seeing conditions but you end up with something like 80mm of aperture in H-alpha which would cost thousands if it were a dedicated h-alpha scope. When it's working and functioning well, this kind of set up offers more rewarding views than a 50mm or 60mm Lunt. Or Lunt 60mm (or 50mm), does what it says on the box, no messing, no cable, nice and simple but with significantly less aperture and at some stage you might want to change the focuser which is a horrid little thing, espeically if you end up hanging larger eyepieces from it like a Delos or Mk IV zoom. In my own case, weighing up all the options and even having a decent frac, I decided in the end to stick with a Lunt 60mm. There are an awful lot of sunny days in Spain and I hate messing about with gear. My general habit is a quick grab n go view and then back to getting on with the day. Hope that helps a little. P.S: Those with a Lunt generally seem very happy with their scope and those with a Quark generally seem very happy with their eyepiece.
  4. We know that cosmic rays (atom fragments that rain down on the Earth from outside of the solar system) are constantly raining down on Earth. The higher-energy cosmic rays are generally reflected away by the Earth's magnetic field and atmosphere while the lower-energy rays can reach us on the ground. By all indication, this means that the planet is around 99.99% protected from space radiation. As you'll appreciate the quantitative biological effects of the remaining 0.01% cosmic radiation is poorly understood and is subject to ongoing research. However, we can make a plausible guestimate. If, for arguments sake, we assume that cosmic rays hitting biological systems on Earth have absolutely no beneficial qualities whatsoever, then we can assume they are a form of radiation. 1 sievert is associated with about a 5% increase in the risk of cancer. Putting this into perspective, a complete CT body scan is about 0.5% sievert, an astronaut on a 24 hour Earth-Moon round trip would receive about 0.0009% sievert while someone on Earth would receive about 0.00009% every day.
  5. My advice: stay active on SGL (probably not going to happen) find an astronomy club in your area and join it ask these people lots of questions at the club, watch folk use their equiptment find a mentor after a few months you will have a better idea whether AP is your thing.
  6. A lucky friend you have Not knowing what accessories the budding astronomer has already, and no idea of budget here are a few suggestions: cheap and effective seating arrangement (ironing chair, drum stool) an evening accompanied under truely dark skies donuts, snacks, sweeties hip flask (purely medicinal use only) proper red torch (not cyclist type) which can be suitably dimmed S&T's pocket sky atlas Baader solar film to make a solar filter equipment case keeping bits and bobs in one place Illustrated guide to astromnomical wonders (Book) Rukl's Moon guide (Book) download Stellarium (t's free) sign up to SGL and ask questions and get involved till your heart's content fingerless gloves, warm hat, warm socks, winter coat and boots big enough to accommodate 2 or 3 pairs of socks note/sketch book, decent pencils, rubber and sharpener to take notes, make plans and sketch what is viewed perhaps as much as two thirds of any given UK year will be tricky to practice visual astronomy. As such an introduction to another astro-related hobby might also be an idea. I have found sketching, pastel, acrylic tutorials, laymen science, art, humanities, history and philosophical books, scale modeling and music have all helped me to understand and appreciate this hobby even more. Other lovely gifts of which a few highlights have included: Little Planet Factory's solar system set (skip to 1:41 to 3:00). Mova's Globes Sky & Telescope's Mars Globe Metal Earth Space Models (**patience needed** skip through to see space related models) New Ware and Real Space resin models that build into impressive kits (**patience needed** not bothered about rockets but love the old satelites, Soyuz, Voskhod spacecrafts and capsules etc) Hasegawa's Voyager (relatively easy build) Vintage Luna Poster And so on. Hope that helps
  7. Welcome to the forum For a very good introduction to astrophotography that will serve you well and will save you a lot of money by making sure you don't head off down some dodgy or misinformed lane or an expensive dead end with equipment - it's worth getting a hold of a copy of Making Every Photon Count by Steve Richards.
  8. I think a 3x Barlow would make a f/5 scope behave like a f/15. In effect, tripling magnification, reducing TFoV by a third and likewise the exit pupil. Depending on the Barlow you may need more out focus to accommodate for the narrower light cone being produced. A possible sollution is to unlock the Barlow-EP combo from the focuser and slowly bring it out and see if you can reach focus.
  9. In terms of visual reference, I tend to avoid images and focus instead on sketches from seasoned observers. Using them as a guide and understanding them as the best representation I'm likely to see myself. The linked video of Saturn probably presents a run of stacked images passed through some kind of software to tidy the image. With a power of 300x and an exit pupil of around 0.3mm it is not a handy guide for visual work. Nevertheless, on any reasonable night of seeing my 4" Vixen offered more visual information of Saturn this late summer than the video. However, no matter how much I worked with my Mak 127, I cannot remember ever seeing the Cassini Division. My Tal 100 achro would struggle and only on the best of best nights does the little TV76 reveal a hair line gap. Taking this into account, when observing planets with smaller apertures not only do the atmospheric conditions, one's experience and visual acuity play a significant role, but so to the quality of optics used. Finally, reading charitably the video and many sketches, I feel that astronomy is a very intellectual hobby. Many of the things we look at are barely visible or are whispering hints of something more just beyond our immediate grasp. Most people think we're nutcases. Sitting out in the cold and dark, observing barely nothing. I also think a lot of people find astronomy disturbing and even frightening. They either don't get it or simply don't want to. The reason we get exited about it and may exaggerate our visual experience is because we know what it is that we're looking at and it is that very knowledge which fuels our kick.
  10. In no manner has my own collection been as exhaustive or as profound as many of the other members'. My telescope history runs as: Tal 100 - my first scope purchased about twenty years ago. Built like a tank, good optics and well corrected f/10 achromatic. To this day, I still consider it a fine first time scope. Worth more than any asking price the Russian gem was donated to charity in 2014. TeleVue 76 - the little 3" is still arguably one of the most attractive scopes I've ever seen. Its primary function was for solar white-light but over the years I have grown to admire its night time capabilities: ease of use, swift cool down, compact, solidly built, with crisp, aberration free views. Lunt 60 B1200 - without doubt my most used scope. My astro-life changed with the Lunt. Now I could star gaze, sip on chilled cocktails and get a tan all at the same time. The revelation was more fundamental than the first time I viewed a faint fuzzy or Saturn at magnification. SkyWatcher 300p Skyliner - nice introduction to the universe 'Beyond Messier'. Decent aperture, quick set-up and good views. Sold in 2019. SkyWatcher Mak 127 - everything about this scope I dislike. Weighty, long cool down dew magnet, narrow field of view, sloppy focus, mediocre optics. Will donate when appropriate charity/club hits my radar. Celestron C8 - relatively light, compact and generally decent scope. However, it was sold on due to narrowish field, off axis aberrations, and uninspiring views. Ottiche Zen 10" Mirror Truss Dob - classic truss dob design, mirror from Italy. Solid, fluid, extremely compact offering outstanding views. If the Lunt is my most used scope this is probably my most travelled. It's been all over Spain and to France, Italy, Slovenia, Austria, Hungary, Slovakia, and the Czech Republic. Vixen FL 102s - absolutely stunning scope with incredible optics. The telescope staggered me at first light and hasn't let me down since.
  11. From my understanding it takes a good few millions of years for a large mass star to gradually die, less than a quarter of a second for its core to collapse, perhaps a couple of hours for that shockwave to reach the outer layers of the star, a few weeks to months to brighten as a Supernova, and then it just fades away with time. I recall observing the supernova in Messier 82 a few years back but can't remember it staying bright in the sky for long. With the 10" in action if I said it lasted a few weeks, I don't think I'd be that far out. Anyway, here's an amazing extract of the death of a star like Betelgeuse:
  12. Just to add to the complication (bear in mind I do not own either type, so just going on numbers)... Weight - + 1 for Ethos Eye relief - + 1 for ES92 On axis - both Contrast - I've always been a sucker for TV's field fo view contrast, so I'm guessing + 1 for Ethos Re-sale - if you bought secondhand and resold, you really wouldn't lose out either way. Focal Lengths - +1 for Ethos (more choice)
  13. Thank you all for such great replies. Its interesting to see what you guys are using and how your eyepiece set ups are in a good state of flux and evolution. The secondhand astronomy market being so poor in Spain and so tricky either to buy or sell decent used gear, I tend to drift towards the dictum, 'Buy once, cry once.' I also try to buy eyepieces that are recognised as working well without any aberration or distortion in any focal ratio scope be it an f/4, f/5, f/6 or what have you. I've found that scopes come and go, but eyepieces more often stay. Like Stu, I have a full set of BGOs. Optically they are outstanding and I used to use them all the time but now I'm older I find them a little tiring to use over extended periods. I also have 24mm and 19mm Panoptics, 14mm and 10mm Delos and Mark IV zooms for binoviewing. I don't have any comfortable, wide field of view, high power eyepieces. For many years I was quite content with just using a Barlow or BGO but perhaps for 2020, I'll keep a look out for a higher power Delos or DeLite and then I think I'll call it a day.
  14. To the question 'what is maximum useful/optimal magnification?' There seems to be a whole range of ideas.... 0.45mm x aperture in mm. 2mm x aperture in mm/50x per inch of aperture. 1mm x aperture in mm/25x per inch of aperture. focal ratio of scope x2 / focal length of scope (2mm exit pupil). focal ratio of scope x1 / focal length of scope (1mm exit pupil). Half focal ratio of scope / focal length of scope (0.5mm exit pupil). TeleVue recommends 2.5x mm of telescope aperture. Experienced observers going way beyond even these limits etc and so on and so fourth.... Depending on who you ask, a 100mm f/10, for example, will either have a maximum useful/optimal magnification of around 45-50x, 100x, 200x, 250x, or more. Plug in other factors like optical quality, collimation, seeing and atmospheric conditions, visual acuity, the type of object being viewed and these numbers may start to vary once again. In other words, all the detail through your scope will be seen at about (a, b, c, d, e) x per mm of aperture and that any magnification above will fail to reveal any more detail, although the detail might be easier to see. Clearly, as this thread is showing, such statements cannot be right. What magnification is useful is evidently variable. As such, all options should be explored when observing, or at least those which maximise the observer's experience.
  15. Just thinking outloud. But it might be worth placing the eyepiece's barrel a little way out of the focuser (cm by cm) and see if it comes to or near to focus. If so, it might be a 'problem' with the primary mirror's placement. If it is possible, raising the primary mirror just a small amount towards the secondary (mm by mm) might help. P.S: If that sounds a but mad, it might be an idea to hunt down a local astro-club and get some of the regulars to check over your system. For sure, it will be purely a mechanical problem which shouldn't take too long to fix. P.P.S: Looking at the photo, also make sure your secondary is at 90 degrees to your focuser and centered. If I'm reading the photo correctly it looks a tad skewed.
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