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[Chicago Astronomer - Astro Joe]

What is the Limiting Observable Magnitude under the Bright lights of Chicago?

Chicago Astronomer reader Herb sent me an email with a rather good question:

Hey Joe.

Thanks for killing the spam bots!

Assuming average human visual accuity and taking into
account the light pollution in Chicago. What would you
say is the limiting Magnatude for the Chicago area?

Thanks.

Herb

Since there are different opinions on observable magnitudes, I deceided to post here instead of answering via email.

In my opinion...

I try to caluculate the evenings limiting magnitude conditions from the heart of Chicago, (about two miles west of downtown), by locating Polaris. Some nights the conditions are so bad that I can't even pick out the pole star. But Polaris is a 2nd Magnitude star and it's sad that at times..even it is hard to catch.

On a good, clear and transparent night I would say the limiting magnitude naked visabilty is "3" and on a very clear exceptional night maybe "4". At mag 3 that's only about 250 stars that are within our sight!

Quite depessing, if you think about it...