Census of stars
Name: Pam J Byrne, Pamela A McDermott, Cynthia M Sauceda,
Janette L Gubalabm, and Don R Judd
How many stars are there?
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!
Visible to the naked eye: a few thousand.
In the Milky Way: around 10 billion; and at least 10 billion galaxies!
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Update: June 2012