Working Out What I Can See....?

[Qualia]

I was wondering if anyone could help?

Imagine I had a 4", 6", 8" and 10" scope and I wanted to do some observing this autumn and I wanted to view deep space objects like nebulae, galaxies and globulars. My skies are averagely okay; not inner city but not hardcore darkness either, and my eyes are averagely okay too, not an eagle but not blind.

What are some of the general data you use before beginning your observing session to appreciate the possibility of whether you will be able to see the object or not? So a priori, you kind of know whether you're wasting your time, have a slim chance or that the object will be a breeze to observe.

Thank you in advance of any input or enlightenment

[swamp thing]

TBH Rob for extended objects its always a tough call on what aperture can see what from where.

Theres so many factors involved its almost impossible to gauge. 

I tend to just suck it and see.

Have a bash at everything is my policy, you never know you may just surprise yourself.

[D4N]

Smaller objects are generally easier to see than big ones of the same magnitude so even this doesn't help much.

It really is just a case of learning what your equipment, eyesight and seeing conditions are capable of.

Sent from my iPad using Tapatalk

[Moonshane]

I think the problem is you are asking (mainly) UK astronomers how they plan an observing session. Planning requires reliable weather and given the UK's poor track record in this area we cannot plan anything in advance with any reliability and appreciate any scraps of good sky we get whenever we can get them

Personally, I just put the scope out and choose an area that is unpopulated by clouds using the star map to guide me.

If I do get a chance to plan, I just use a planisphere to choose the best areas, then highlight any DSOs in those areas not yet seen (usually using Sky and Telescope's Pocket Atlas) and try my luck. Sometimes it works and sometimes not.

In short I think unless you have really good weather, planning is a bit of a waste of time in the UK unless of course you count the enjoyment of checking out maps and reminding yourself what you have not seen yet

[Knight of Clear Skies]

One thing I've been using to work out what targets I can image with my camera lenses is this 360 degree Milky Way panorama. It's been calibrated to have the same relative brightness across the sky and I have a fair idea from my previous efforts what brightness levels I can pick up. Might be of some use to visual observers as well, although the resolution isn't high enough for small objects.

Hope that's some help.

[RikM]

I also just give it a go and see what I can see. I'm working through the "SAC 110 best of the NGC" booklet and am pretty confident I will be able to see all the objects listed. The NGC descriptions also give a good idea what to expect.

[Qualia]

Arrr, I'm disappointed with those answers, gentlemen I thought you guys were going to offer some magic p x q / x formula that would whisk my troubles away.

I guess you're all spot on; best to just bite the bullet, get on with it and see how it goes, that weather conditions are not exactly conducive to any significant level of planning and even if they were, there are so many factors involved that the issue of calculating what you might be able to see remains mute

Anyway, thank you all for your replies and excellent insights

[jetstream]

I check the "greyness" of the sky, how the constellations look and whether any stars are visible near the horizon. This gives me an indication of sky transparency and how light pollution will effect sky darkness. Its amazing how suspended dust, aerosols, whatever can reflect LP and kill the sky. If the constellations are easily visible, but they are "all alone" ( not good)  I pick star asterisms/clusters like ET, the Muscle Man ( best in poor conditions),Pleiades, M13 and nebs like M27 and M57. The horizon star check also tells us about light extinguishment...if there are no low stars visible or they are poor its over to the objects listed above. Double stars are a favorite then too, the atmosphere can change and sometimes enhance the beautiful "color" doubles, Izar, Almach and Albireo are among the favorites. I tend to use my refractors- 90mm and 120mm under these conditions, SQM of 19 mag or less.

But then the sky can magically seem blacker, clearer and cleaner-from any location ( SQM 19.5+)- and out comes the bigger scope.  Galaxies like M81, M82, M31, M110, M32, the Leo Triplet are all viewable as are others. The Veil with an OIII will be reasonable ( like last night) and M27, M57 will be great. I check galaxies for a surface brightness similar to M81, M82  and know they will be good if similar or even a bit fainter. The 3.5"-4.5" scopes will do good under these conditions too, but extra aperture really helps.

Technically the magnitude of the sky, light extinguishment and NELM are what I use to assess the conditions and then pick appropriate surface brightness DSO from the list. The better the sky the more aperture I'll use- keeping in mind that more aperture- up to some limit- will almost always help.

[cotterless45]

I do a list of most stuff down to mag.+12. Don't forget some of the dim planetary nebulae and galaxies have a bright spottable core.Usually it's so nightmare to see anything remotely faint from home. I use the formula,

T= 1/m + 1/s

Where T is the amount of time spent looking and m is the magnitude and s , is so given up !

Higher magnification helps cut through the glare of light pollution to enter the wonderful world of clusters, double stars and planetary nebulae, hurrah !

Nick.

[webboid]

In making the choice of which scope I am going to use for DSO observing the 12" dob always wins. I observe from several sites NELM 6.5 & home with NELM at best 4.8. In order to determine whether I will be able to view xyz object I tend to rely on surface brightness data obtained from Kepple & Sanner "The night sky observer's guide" in tandem with experience of other objects observed from the site I am observing from. I often use familiar objects to assess the sky M51, M101, M33, NGC 891 & so on.

I was recently observing from a dark sky site I use where I have seen galaxies with surface brightness dimmer than 13. But conditions were poor & I struggled to see any of my planned targets. Knowing what I had seen there before & using them as a reference that night it was apparent that my plan was scuppered. However they should be visible on another night from that location with better conditions. So I just retain the list for a future session.

On some occasions a surprisingly good sky develops in an unlikely location. From home observing in Virgo just over the roof of my house in the skyglow I was able to clearly identify over 20 galaxies there. An exceptional night that would have been missed if I had not at least tried.

You say "What are some of the general data you use before beginning your observing session"

I refer to records of previous observations at my particular observing site to confirm what has been possible. Look at previous observing plans not completed. Make an assessment of the sky on the night of observing. Be persistent as conditions change. Use surface brightness data of DSO rather than magnitude. Start with familiar targets that I know what they look like as a guide to likely success on the new targets. But I think experience at the eyepiece allows the observer to become more skilful at seeing what is there & may have been visible in your chosen scope all along.

HTH.

[jetstream]

I do a list of most stuff down to mag.+12. Don't forget some of the dim planetary nebulae and galaxies have a bright spottable core.Usually it's so nightmare to see anything remotely faint from home. I use the formula,

T= 1/m + 1/s

Where T is the amount of time spent looking and m is the magnitude and s , is so given up !

Higher magnification helps cut through the glare of light pollution to enter the wonderful world of clusters, double stars and planetary nebulae, hurrah !

Nick.

LOL! Good formula Nick!

[Qualia]

Great replies, and thank you When and if these clouds and dry lightening storms clear, it'll be back to mirror and glass to see what can be tweaked from the heavens. Really fancy seeing if I can spy something of the Galaxy cluster in Pegasus (7317 et al)