Determining Light Pollution

[Falcon]

Hi, I'm wondering if theres a method in which i can calculate how light polluted my skies are.

I was out two nights ago with my scope, I was looking for a few galaxies around Ursa Major and the Glob M13 i think.... I had no luck at all. I was using my starry night program to star hop and i thought i was on the right track. But i saw nothing. I think the light pollution is too much....

[skywalker]

You didn't mention the magnitude of stars visible, Tho fortunate to live near rural area in Midwest, still lots of lights, difficult to find a true dark sky... My area use close by is right on the edge of small town, lights only just over 2 blocks away, but still pull in near or just over 5th magnitude stars in south, forget it in the North, closer to and even below 4th but not anyway near 5th magnitude...area is very open near 360 degrees and again close by... What magnitude stars are you seeing can help, but that's not the complete picture, also sky conditions as clarity, steady seeing... Amazing to me some of the best observations were close to or rather hazy skys, as goes along with steady seeing, stars don't twinkle or very little, unfortunately a rare treat... Current object I use alot to know immediately of what the views will be is the famed Trapezium, if the additional 5th or 6th come into view, I'm in for a very good observation session... Far as the light you have to contend with, only hope is to move away from the lit area if possible, however planets do-not require dark skys at all, can look at Jupiter under a steet-light and still pull in details... Galaxies are abit more elsusive, the other day pulled in either Owl Nebula or the Galaxy nearby, conditions so bad couldn't tell which I had, during fair to good conditions the Galaxy was large spindle like, tho the Owl was not defined larger then prior views...

[doriscrisp]

I have always used Ursa Minor as a rough estimate of limiting magnitude, as it covers a good range from 2.0 down and includes stars of pretty much every magnitude down from there. There are plenty of charts online and the one linked below (second chart on the page) is pretty good for what you need.

Of course limiting magnitude will be different in different parts of the sky, depending on elevation of the star, where the local light pollution is coming from etc. As a rule of thumb, 5.5 in a suburban setting is pretty darn good.

I'm a little surprised that you can't find M13. I would have thought it was almost naked eye in anything better than moderate lightpollution, even if only using averted vision.

[admin]

There is also a more accurate method of determining limiting method which is used by the International Meteor Organization (IMO). It involves counting the number of stars visible in certain areas of the sky. Then you just look up a table and from the number of stars that you can see, you know the limiting magnitude in that particular part of the sky.