Local sky darkness

[jetstream]

I was wondering what typical limiting magnitudes guys have in U.K. on nights of good seeing?Our weather seems similar and am finally finding DSO's from my yard.4.6 magnitude was the faintest star I could see,but here is my list last night:m4,m8,m13,m20,m22,m27 &m31.Not the best views but I could see them,is this typical?

[umadog]

It all depends where you live. The best tool for this purpose that I know of for North America is: http://www.jshine.net/astronomy/dark_sky/ The colours are described on the clear sky clock e.g. this is the clock for my local site: http://cleardarksky.com/c/CstrInsNYkey.html and: http://cleardarksky.com/lp/CstrInsNYlp.html?Mn=astrophysics

"Seeing" has a specific meaning, though. It is the term that describes the stability of the atmosphere, so it's not a general descriptor of sky quality. A given night may have good seeing (still atmosphere) but poor transparency (clarity or opacity of the sky). On such a night, the limiting magnitude will be poor but the stability of the air will make it a good time to chase planets and double stars.

The colours are related to the Bortle Scale: http://en.wikipedia.org/wiki/Bortle_scale The motivation for the scale is that limiting magnitude can vary a surprising amount between observers, whereas the criteria on the Bortle scale are a little more robust.

So your back yard is roughly Bortle 6 or 7. You could try for M31 naked eye when it's higher in the sky. You description of what you can see is quite consistent with such skies.

[jetstream]

Thanks again umadog,I'm looking at the dark sky finder site...in between International falls MN and Thunderbay Ontario there is a smallish patch of darker zone.So the transition from grey to black(or darker grey) would be an improvement of?If a guy zooms in I may head in on the Manion lake road which is darker by a "shade" than the other dark spot but further away.Looked at the Bortle scale-new to me again.Your light prediction for my house matches this.Skies look good so I'm deciding on which place.Site is about 50 miles from Fort Frances west on Hwy 11.Andromeda low in sky was washed out bad as pollution in that direction is worse-nothing as good as I've seen away from here.

[umadog]

Oh wow! You don't know how lucky you are, my friend. Smallish patch?!? That's a HUGE patch. See that blue stuff? I drive 4 hours to get blue stuff like that I consider myself very happy indeed when I get there. That gray and black stuff? I drive a whole day (days in one case) to get to skies that dark. Once a year is all I get.

Of course, at this time of year you won't get much darkness but come the fall you ought to have easy access to really dark skies. "Blue" skies are really nice. M13 and M31 are obvious to the naked eye, etc. Very pretty. The "gray" and "black" stuff is just breathtaking. Dark nebulae become really fun objects. The spiral arms in M33 are obvious and the galaxy itself is a naked eye object. The difference between gray and black will probably relate to stuff such as distant light domes. No hard and fast definitions. Looks like 45 minutes out of Thunder Bay will yield some nice skies, though.

[jetstream]

Thats great to know umadog,I never realized the "grey" area was so good!Our cabin is into that area by about 10 miles...Last winter the sky blackened and it LIT up like a Christmas tree!I had just bought my scope then & only knew couple of objects,but the Orion nebula was stunning.The two things here are the clouds-clear this morning but now clouding up again,same as last night...cleared at 10:00 & I ran out with my scope until 1:30am!Another issue is the trees & rocks,very hard to find a good spot-BUT- on that logging road (manion) I found 2 clearings not too far up,4km & 7km.I fish up there so I know it somewhat.So on my other post about scope size for DSO detail...with that darkness & good seeing would you go 8",10" or 12" Newtonian?I know bigger is better,however....Oh yeah I can be long winded & blab away!lol!

[umadog]

Bigger is generally better, although obviously bigger is harder to move and set up. Even in light polluted skies a larger scope will show more. Small, bright, objects like planetary nebulae always benefit from aperture. Also, you get more useful power with an OIII or UHC filter in a larger scope. That said, the difference between, say, an 8" and a 12" only really makes itself felt in dark skies (better than about Bortle 3 or 4). If you have easy access to such skies then absolutely the bigger the better.

[jetstream]

I do have access to these skies,on the ice in the winter,roads in summer to fall.I'm pretty excited to know about the potential around here & maybe for fall I can look at a Dob.Ok I'm not a computer guy(please excuse the spelling/keyboarding mistakes) and so if I want to talk scopes now should I start a new thread?I see you have some TOP quality optics & had a few more questions...

[umadog]

Yeah, start a new thread so more people will chip in.