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Counting Stars

July 26, 2013

The Milky Way arcs across the east as the sky gets good and dark this evening, from the hook of Scorpius in the south, through the body of Cygnus, the swan, in the east, to W-shaped Cassiopeia in the north. It climbs higher as the night goes on, although the Moon spoils the view when it peeks into view before midnight.

The Milky Way outlines the disk of our home galaxy, which is quite impressive. It’s a hundred thousand light-years wide, and about 10,000 light-years thick. Bright young stars in the disk trace out spiral arms, which extend from a thick “bar” of stars in the galaxy’s center.

Just how many stars the Milky Way contains is uncertain. Estimates range from a hundred billion to as many as a trillion.

It’s impossible to actually count the Milky Way’s stars. The sheer numbers are one problem, while another is that most of the stars are far too faint to see even with big telescopes.

So astronomers must estimate the galaxy’s population. In part, they do so by counting the stars that are close to us, then extrapolating for the rest of the galaxy based on the types of stars, the size and mass of the galaxy, and other factors. Yet there’s still a good bit of uncertainty — providing a wide range of estimates for the number of stars that fill that hazy band of light known as the Milky Way.

If you’d like to count up some of those stars yourself, find a dark spot away from city lights, then gaze deep into our galactic home.


Script by Damond Benningfield, Copyright 2013

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