# Astronomers say there are more stars in the universe than there are grains of sand on all the beaches on earth. How do they know how many grains of sand there are in the whole world?

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Astronomers say there are more stars in the universe than there are grains of sand on all the beaches on earth. How do they know how many grains of sand there are in the whole world?

In: Mathematics

How do they know how many stars there are in the universe? It is an ever-changing number. As we see more distant galaxies we have to increase our estimation of stars.

According to astronomers, there are probably more than 170 billion galaxies in the observable Universe, stretching out into a region of space 13.8 billion light-years away from us in all directions.

And so, if you multiply the number of stars in our galaxy by the number of galaxies in the Universe, you get approximately 10^24 stars. This is a minimum value based on the observable universe.

The Universe could be much bigger. It’s even possible that the Universe is infinite. What defies belief though is that the game of chess still has more moves – 10^120, as shown by the [“Shannon Number”](https://en.wikipedia.org/wiki/Shannon_number)

Follow up question. If there are seven quintillion stars, why is the night sky black and not white?