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harrym

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Everything posted by harrym

  1. Saw this tonight with the 12" refractor in Cambridge. It's quite tough and is definitely nowhere near the mag 13.2 or 13.6 that has been claimed - it's probably 14.5 if that, and the fact that it's not against a completely dark background doesn't help.
  2. Last night was the first good chance for me to observe with the 12" refractor since I got back to Cambridge a couple of weeks ago. The forecasts didn't all agree that it would be clear, but after 8pm the clouds dissipated so I decided to give it a go. First I had a look at M57, because why not? Then the clouds came in. 45 minutes later they unexpectedly disappeared, and didn't come back. Here are the objects I observed: NGCs 6802 in Vulpecula, 7128 in Cygnus and 7296 in Lacerta - all open clusters small enough to fit in the FOV. None of these seemed particularly interesting so I prob
  3. Just saw this quasar again. The conditions weren't nearly as good as last time, but I think it's a bit brighter now than it was in August. Back then it was fainter than the star I marked "14.9?" on my chart which I posted earlier in the thread, and I estimated it was around magnitude 15.2, but this time it was the same brightness as the 14.9? star or maybe even a little brighter - perhaps 14.8. Now's the time to give it a go before it gets fainter again!
  4. Its closest approach was yesterday, and it didn't get brighter than 19th magnitude so I doubt anyone saw it.
  5. Get a red torch - red light doesn't harm your dark adaptation much, but it will allow you to read the book. If I were you I'd get an adjustable one, as you'll probably want a brighter light at home than at a dark site.
  6. That is correct, but only because no-one even knew it existed before the photographic era - it was discovered photographically! P.S. Never even tried the Horsehead - don't have a Hb filter so there isn't really any point.
  7. Quasars are often variable so it could change brightness, yes. But as it's only recently been discovered we don't know anything about its light curve. It seems to have been recorded as a magnitude 14.9 'star' in some catalog (can't remember which one), whereas combining the magnitudes from the initial paper suggested 14.5, and visually it seemed more like 15.2. As these measurements were all at different times I guess this could be a sign of its variability?
  8. This discussion of not being able to fit objects into the FOV reminded me of Stephen O'Meara's story about observing M57 with the 42" scope at Pic du Midi. Apparently he put in an eyepiece that gave 1200x magnification and was surprised to only see two stars and no nebula. Then he realised the FOV was entirely inside the ring! Minimum magnification = aperture / fully dilated pupil diameter if I've got my sums right.
  9. Thanks for the tips John! Didn't realise the Pup was visible with such a small scope. I've never actually tried it myself, but we have two big refractors and a few orthos in Cambridge so I'll definitely try and give it a go this winter.
  10. Inverting and reverting always gives an image that isn't reflected, but the angle of rotation depends on the positions of the mirrors/prisms relative to the direction you're viewing from. For example, a vertical Porro prism appears to rotate the image 180° (and reverses the direction of the light), but a horizontal Porro prism doesn't appear to rotate the image at all. This is highly counterintuitive but it seems to be correct. See the image below, and always imagine you're viewing the light coming towards you.
  11. Has to be an even number for the same reason I mentioned before. You could do the Porro prism effect with 4 mirrors I think? (Edit: but this might cause distortions...) Does anyone know how those 45 degree image erecting diagonals work?
  12. I think it's to do with even/odd numbers of mirrors. In the Newtonian there are two mirrors and each mirror flips the image once, so the image you see isn't flipped (though it is rotated 180°). However, a refractor with a diagonal has just one mirror (in the diagonal) and a catadioptric with a diagonal has three, so the image is flipped.
  13. Thanks - this is Type II so it should hang around for a while. Will have to give it a go with the 12" when I get back to Cambridge in a couple of weeks.
  14. Don't you mean NGC 457 - I think 147 is a galaxy?
  15. It's trying to show the dark nebula Barnard 22. IC 2087 is the little bright nebula in the middle of B22.
  16. There's still time to catch M11 this year. The Coathanger cluster is a good binocular object, and no-one's mentioned M71 or M103 yet. M81 should be doable but M82 might have to wait till it's higher in the sky. M32 and M110 are also possible given dark enough skies - I saw them with a pair of 8x56 bins from a site with NELM around 6 when I was a novice.
  17. Wow - a clear night! Haven't had many of those in the last few months. Some nice targets as well, though at magnitude 14 you'd need an incredibly dark sky to see Pluto with a 127 Mak. Just wondering, could the alignment issue be anything to do with daylight saving i.e. time zone is effectively +1 hour at the moment?
  18. Nice report! I haven't got a great horizon so I've seen my last of Sagittarius this year. Want to give the Omega a proper go but it'll be a while now till I get a chance. M16 isn't the Eagle Nebula by the way - it's just the associated cluster. The actual nebula has the designation IC 4703, and was discovered in 1876 (with a 26" refractor!), more than a hundred years after the cluster.
  19. The Virgo cluster is great fun - basically point the telescope in that region of sky and there'll be a galaxy in the FOV. Although Mars will be at its closest for about 15 years next year, at opposition it will be at something like -25 declination so not a great position! I'm looking forward to the close approach of comet 46P/Wirtanen in December 2018 - should be 3rd or 4th magnitude and a very nice binocular object, and we haven't had any comets that bright for a while.
  20. It was about mag 10 last night. It's fading quite quickly now - should be down to mag 11 by Saturday. Hope you get another chance to see it!
  21. Finally got a chance to see it with the 8" dob tonight. It's great to be able to watch something moving so quickly - I've seen a couple of comets moving through the field of view before but nothing this fast. The only moon I could see tonight was the big bright one though...
  22. I think the people who are saying 13th magnitude weren't talking about Bortle 1 skies. From lots of Britain, for example, 13 is a realistic limiting magnitude for a 6" scope. Whether you can actually see to 15.5 shouldn't really matter here. The important thing is that from those skies you will be able to see some details in galaxies and nebulae with a 6" scope that are essentially impossible to see with any scope from a light-polluted sky; on the other hand, even from a light-polluted site a large enough dobsonian will show magnitude 15.5 stars.
  23. 15.5 is based on the assumption of Bortle 1 skies, so NELM between 7.5 and 8, and high magnification. Under most circumstances 15.5 with a 6" is out of the question. 15.5 is close to the limit of the 12" refractor in Cambridge (NELM ~6). Experience does play a big part as well, especially with seeing those spiral arms. How often can you get to Bortle 1 skies? Where do you intend to do most of your observing?
  24. 1. Yes, easily. Pluto is magnitude 14.2 I think. Under Bortle 1 skies (I wish I had some of those!) your scope should have a limiting magnitude of 15.5 or better. (Note that you won't see moons of Saturn that are this faint, because of the glare from the planet.) But Pluto looks just like a star, so either you need a star chart that goes down to about magnitude 14.5 or you need to sketch the field on two different days and see which "star" moved. 2. Do you have a hydrogen-beta filter? If so, then probably yes from reasonably dark skies. It might be doable from a Bortle 1 site without a fi
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