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Comet C/2012 S1 (ISON)

tuxcat

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I have a couple questions re. Comet ISON

a) The green ion tail is apparently due to cyanogen and diatomic carbon; what does this mean? Does this give any indication of where it's come from in the solar system?

b) At it's perihelion it will be around 1 degree from the sun (from the observer's position); is there still a chance to see it with the naked eye? How about a telescope with a solar filter attached - will it be visible and safe to look through a telescope or should I put a camera in the eyepiece instead?

Thanks for your time, sorry if these questions sound daft though. I have Googled but haven't found any answers.
 
tuxcat said:
a) The green ion tail is apparently due to cyanogen and diatomic carbon; what does this mean?
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How much detail are you looking for here? Comet tails form when matter is thrown off them due to heating from the Sun. The tail will largely consist of the more volatile components, ie. the ones with lower boiling points which often means organic and carbon-based compounds. All atoms, molecules and ions have different emission spectra, so by analysing the light from an object it's possible to work out what species must be present. Dicarbon and cyanogen happen to have emission peaks corresponding to the green part of the visible spectrum, so the tail appears somewhat greenish to the human eye.

Does this give any indication of where it's come from in the solar system?
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If anything, the reverse is true. All comets are thought to come from either the Oort cloud or Kuiper belt, depending on whether they're long or short period comets respectively, and we can tell that by looking at their orbit. Analysing what they're made of can help us learn what conditions are like where they came from, rather than their conditions telling us where that was.

b) At it's perihelion it will be around 1 degree from the sun (from the observer's position); is there still a chance to see it with the naked eye?
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It would be difficult but probably not impossible to see around perihelion. There will probably be a better chance to see it later when it is further from the Sun but may still have a negative magnitude. Predicting exactly what will happen to a comet is tricky at the best of times though, so there's no guarantee it will even still exist by that point.

How about a telescope with a solar filter attached - will it be visible and safe to look through a telescope or should I put a camera in the eyepiece instead?
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Solar filters work by blocking the vast majority of the light coming in to the telescope. While they can make it safe to view the Sun directly, you'd need one hell of a bright comet to be visible through one.

On the other hand, C/2012 S1 should be visible to a telescope right now, so if you have access to one there's no need to wait until it's near the Sun.
 
Thanks for the replies everyone! So the tail is from volatiles being shed - that makes sense!

The solar filter doesn't seem that good an idea after all - I take it that the filters aren't hydrogen/helium specific and are more of a blanket filter?

I'll see how I get on tomorrow morning at 5.30 am as it's been calculated to be over the horizon by that time. It's currently wet and windy here though. There is one advantage to being semi-rural; you can just grab the 'scope and go without needing to drive for miles to get clear sky on account of urban light pollution. There's a huge field (used for offroading) about 2 1/2 minutes walk behind the house so I can just set up there. It's very dark and very convenient at the same time.
 
tuxcat said:
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The solar filter doesn't seem that good an idea after all - I take it that the filters aren't hydrogen/helium specific and are more of a blanket filter?
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Filters like mylar or glass solar filters used in front of the objective are safe on the sun.
They are indeed like a blanket filter. Glass (some or all?) and mylar solar filters will change the color of the sun's image somewhat, but will not give you any spectral advantage.
The Baader film is supposed to give you a proper white solar image.

NEVER use an eyepiece solar filter visually in your telescope, as the concentrated heat may crack the filter and damage your eye permanently.

As Cuddles mentioned already, a solar filter will render a comet not originating from fairy tales entirely invisible.

tuxcat said:
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I'll see how I get on tomorrow morning at 5.30 am as it's been calculated to be over the horizon by that time. It's currently wet and windy here though. There is one advantage to being semi-rural; you can just grab the 'scope and go without needing to drive for miles to get clear sky on account of urban light pollution. There's a huge field (used for offroading) about 2 1/2 minutes walk behind the house so I can just set up there. It's very dark and very convenient at the same time.
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The Sun and comet are quite far apart currently, the Sun should be no problem currently.

Good luck with spotting the comet and with the weather. I'm looking forward to reading about your observation.
 
tuxcat said:
I take it that the filters aren't hydrogen/helium specific and are more of a blanket filter?
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There are different types. Many are just blanket filters that reduce all light pretty much equally and are used to view the Sun as it would normally appear, just with reduced brightness so you can actually look at it. You also get hydrogen-alpha filters, which block everything except the hydrogen alpha spectral line, and can be used for viewing solar flares and other coronal phenomena.
 
Sadly it's been pouring of rain and when it's not raining it's overcast so I haven't been successful. It's really frustrating I can tell you, but I'm still hoping that this week will be better weather-wise. I'll also have an attempt at photographing it via the telescope (there's a camera attachment like a tube that you put the camera's lenspiece into).
 
tuxcat said:
Sadly it's been pouring of rain and when it's not raining it's overcast so I haven't been successful. It's really frustrating I can tell you, but I'm still hoping that this week will be better weather-wise. I'll also have an attempt at photographing it via the telescope (there's a camera attachment like a tube that you put the camera's lenspiece into).
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Sorry to hear about the poor wheather.

As far as photography is concerned:
Do you mean an eyepiece adaptor, as in, adaptor goes into the focuser, eyepiece goes into the eyepiece adaptor and dslr camera goes onto the adaptor with a T2 ring?
Or do you mean attaching the dslr camera to the focuser and using the telescope as a lens?
Or do you mean a-focal photography through the telescope's eyepiece with a dslr or compact camera?

Do you have decent tracking capability on your telescope mount?
 
It's essentially an attachment that instead of putting your eye into the eyepiece you can attach your camera to the telescope and use it as a telephoto lens, I think It's designed for regular digital cameras as an SLR lens unit would be too big. I'm not sure if it came with the telescope or it's an extra as it came as a present.

It's hard to describe to be honest and at the moment I have a cold and am not very lucid (you'd never have guessed would you!). I'll do some pics which would be better than trying to describe it.
 
I've just remembered - the tripod attachment for the telescope broke due to over-tightening (think the torque fractured the plastic) so I think that photos are out of the question as it'll just be a blur. I'll have to use superglue to stick the ring back together again as that'd be easier than holding it and getting tired arms.
 
Well, that your mount broke is a pity.
However, if the comet develops a large tail, you might as well try your hand at long exposures (in your case perhaps 15 seconds maximum) with aperture wide open, from a tripod or any sturdy support for the camera in manual mode or any mode allowing such exposure times.

A (properly tracking) telescope would then (long comet tail) give too small a field of view to appreciably image the comet.

If the comet is very bright you may have to experiment with a range of shorter shutter speeds or/and close the aperture a bit.
 
The comet is allegedly eye-visible; I'm told almost magnitude 3 - but I couldn't see a ghost of it this morning in 100% clear skies. The moon is pretty bright, so I figured it was washed out - but at 3.5? I think I still should've seen it.

Eventually not far above the horizon I saw a brightish dot (with no tail) that I took to be Mercury, as my astronomy software showed it rising at that time. However, halfway between Spica and that dot - where the software said ISON should be, well above the horizon at that point - nothing. I don't have binoculars or a scope, sadly; however, at least from a naked eye standpoint the Great Comet of 2013 should more accurately be called the Meh Comet of 2013.
 
I've now recovered from my cold. What I'm planning on doing is forgetting the photography part of comet-sighting as it'll just be a blur as there's no way that I can hold a telescope steady. It's still overcast and raining - and now blowing a gale so I've been thwarted yet again :mad:
 
I should point out that right now on PBS there's a very interesting show about lightning sprites. It's called At the Edge of Space.
 
I will watch the show; I am quite interested in this comet. However, the description:

Right now Comet ISON, somewhere between one and 10 kilometers in diameter, is just beyond the orbit of Jupiter. As it races past us toward the sun it should develop a tail that will light up the skies brighter than a full moon. Then the comet will slingshot around the back of the sun and could emerge brighter than ever, treating the entire northern hemisphere to an unforgettable sight.
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...was obviously written some time ago; the comet hasn't exactly delivered as advertised yet - and considering that perihelion is only a week hence, I don't see it delivering, either.
 
Hey I'll admit I might be. If I'm wrong, I won't feel bad because that will mean the comet is spectacular.

But again - it's only a week to perihelion. Is there a history of comets which weren't all that visibly-exceptional initially, suddenly becoming prominent less than a week before perihelion?

I realize also that once this comet rounds the Sun it might be much brighter as well; but I was under the impression that it was this comet's pre-perihelion phase that was going to be the most visually striking - I could be wrong about that too.
 
Everything I've heard has said it should be brightest after perihelion, peaking in mid-late December (if it survives perihelion, of course). First heard that many months ago. Closest approach to Earth is Dec. 26.
 
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