by William Remski

Created on: September 12, 2007

The only way to determine the number of stars in the universe is to estimate the number. We cannot even count the number of stars in our own galaxy, because they are hidden by lanes of dust and clouds of ionized gas. Star surveys used to be a bigger part of astronomy before the true structure and nature of the universe was known.

The first way to estimate the number of stars is to start counting them. You will need to take a photograph of some area of sky. You will need a microscope to see all the tiny specks that are distant stars. You will not live long enough to count the number of stars even in our own galaxy. This number is about a hundred billion. If you spent one second counting each star, every minute of your entire life for seventy years and did nothing else you would only count to 2 billion, 207 million. It is impossible to directly count the number of stars. Still, in a single afternoon you could count all the stars on a photographic plate and multiply that number by the number of plates it would take to cover the entire galaxy, and you would come up with a rough estimate of the number of stars in the galaxy.

That's just one galaxy. The thing is, there are billions and billions of galaxies, as Carl Sagan would have said. How do you count the galaxies? Same as stars, take a picture, count the stars on the photo, than multiply by the number of photos it would take to cover the entire sky. Now, multiply the number of stars in one galaxy by the number of galaxies and you have an estimate for the number of stars in the universe.

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