Wednesday, August 18, 2010

About how many stars are there in the universe?

This is a tough question, since we do not know the precise number of stars in the universe. If we were to simply look up at night sky, we can see an extremely large number of stars. We can use a telescope to increase the distance at which we can observe a star. Still, there are so many more stars we cannot see, which means we have to make certain approximations to answer this question. 


Our own galaxy, the Milky Way, contains about 100 billion stars. If we imagine that galaxies are spread throughout the universe uniformly, we come at an estimate of about 10 billion galaxies. Multiplying those two numbers, we get an estimate of about 1000 billion billion stars or `10^21`  stars. 


Note that this estimate only includes the stars in the observable universe. Since we estimate the age of universe to be around 13.7 billion years, we cannot see any stars or galaxies that are beyond 13.7 billion light years away.


Hope this helps.

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