It's an estimate based on the average number density and volume.Originally posted by ShadowKnight
I was looking at some maps of the known universe (http://www.anzwers.org/free/universe/) and a question occured to me - how can astronomers say how many stars are in a certain galaxy? What method is being used to count them? Is it direct observation or is it some kind of formula?
this is a pretty interesting questionOriginally posted by chroot
It's an estimate based on the average number density and volume.
tho not an expert I will tell you how I understand those numbersOriginally posted by ShadowKnight
OK, that makes sense to me. So I wonder if astronomers take any dark matter into consideration when they make their estimates. I've heard compelling evidence that it exists (though unproven?) On one map of the galaxy (http://www.anzwers.org/free/universe/milkyway.html) it shows this data in a table:
Number of stars in the Galaxy: 200 billion
Mass of the Galaxy: 1 trillion solar masses
Ignoring any dark matter this would mean that they came up with an average of 5 solar masses per star. How do gas clouds and nebula and other non-stars in the galaxy get figured into this?