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Name: Pam J Byrne, Pamela A McDermott, Cynthia M Sauceda,
               Janette L Gubalabm, and Don R Judd
Status: Other
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Question:
How many stars are there?



Replies:
Well, you could try counting them :-) From my house you can only see about 200 or 300 most nights, because the street lights get in the way. In principle, on a dark night in some isolated area of the country, there should be several thousand visible. You will also notice a kind of hazy band extending diagonally across the sky - this is the Milky Way, our home galaxy. The hazy band actually consists of millions of stars too faint for us to resolve without using at least binoculars, or of course telescopes. Nobody's counted all the stars in the galaxy - I believe the number that have been counted is on the order of a million. But in fact, by looking at other galaxies that seem to be about the size of the Milky Way, their overall brightness implies that they contain roughly 10 billion stars - much more than we can see, or count easily. Put another way, that is several stars in our own galaxy for each person here on Earth. But there are also lots of galaxies out there - in fact, you can even see a few of them on those dark nights when you can see the Milky Way with your bare eyes. Using telescopes, we find more and more of them, out to immense and almost unimaginable distances - billions of light years. Again, nobody's counted all the galaxies, although I believe several hundred thousand have been catalogued. But just from the immensity of the space we can observe, and the average distribution of galaxies in it, we can guess there are 10's of billions of them also. That means the number of stars in the universe is really enormous - 1 followed by 20 or more zeros!

A Smith


Visible to the naked eye: a few thousand.
In the Milky Way: around 10 billion; and at least 10 billion galaxies!

Hawley


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