The Stellar Census: 70 Sextillion

Imagine all the stars littering the dark sky on a clear, moonless night, miles from the glowing city -- and then multiply that number by more than a million million million. You would come fairly close to the total number of stars that can be viewed by the world’s most powerful telescopes, according to a new astronomical survey.

There are approximately 70 sextillion -- that’s 7 followed by 22 zeros -- stars in the known universe, a team led by Australian astronomer Simon Driver announced this week at the 25th General Assembly of the International Astronomical Union in Sydney.

That means there are more stars in the sky than there are grains of sand in every beach and desert on Earth -- substantially more than the 100 or so stars visible from downtown Los Angeles or the 2,000 stars that can be seen from Mt. Wilson Observatory high above the city in the San Gabriel Mountains.

The astronomers made the calculation with observations from the Isaac Newton Telescope in Spain and the Anglo-Australian Telescope in New South Wales as part of a project known as the Two-Degree Field Galaxy Redshift Survey.

First, they determined the density of galaxies in a strip about a thousandth the size of the entire night sky and then figured out approximately how many stars are in each galaxy. Using the results, they estimated the number of stars in the galaxies visible to the two telescopes.

The astronomers did not originally set out to count stars -- it was simply an interesting side result of more serious research into the evolution of galaxies, which will be published by London’s Royal Astronomical Society.

“Finding the number of stars is not really the research we were doing,” said Johns Hopkins astronomer and co-author Nicholas Cross. “But it was a nice result to play around with.”