# The Naked Scientists Forum

### Author Topic: Are there more stars in the Universe than grains of sand on Earth?  (Read 1558 times)

#### Harri

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##### Are there more stars in the Universe than grains of sand on Earth?
« on: 16/10/2015 19:55:20 »
Hi all,  a friend told me that there was more stars in the universe than there are grains of sand on the whole planet! Is this correct? If that were true just how many planets and moons would we be talking about?
« Last Edit: 16/10/2015 20:36:00 by chris »

#### chiralSPO

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##### Re: Are there more stars in the Universe than grains of sand on Earth?
« Reply #1 on: 16/10/2015 22:08:57 »
Well, we don't know how many stars there are in the whole universe, but in the part of the universe we can see (the observable universe), there are about 1021 stars (that's 1000000000000000000000 stars).

How many grains of sand on the Earth? a quick google search offers 1018. Even if they are underestimating by a factor of 100, that's still 10 times as many stars that we could theoretically see.

As to how many planets and moons there are... Recent work looking for and studying exoplanets suggest that stars have between one and two planets on average (that we can detect). Many of these may be too close to their stars to have stable satellites, but I would hazard a guess that any given star would have around a dozen orbiting bodies that are large enough to pull themselves into spherical shapes (our own solar system has at least 32 confirmed spherical bodies https://en.wikipedia.org/wiki/List_of_gravitationally_rounded_objects_of_the_Solar_System)

So there could be 1022 worlds in the observable universe, a full 10000 times as many as there are grains of sand on Earth.

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#### Harri

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##### Re: Are there more stars in the Universe than grains of sand on Earth?
« Reply #2 on: 17/10/2015 20:02:42 »

It's a lot for a small human brain to take in but you put have put it quite succinctly and I find it quite mind blowing!!!

#### chiralSPO

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##### Re: Are there more stars in the Universe than grains of sand on Earth?
« Reply #3 on: 17/10/2015 20:24:21 »
Even more mind blowing (I think) is that there are >1000 times as many atoms in a glass of water as there are stars in the observable universe!

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#### PmbPhy

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##### Re: Are there more stars in the Universe than grains of sand on Earth?
« Reply #4 on: 18/10/2015 00:11:23 »
Hi all,  a friend told me that there was more stars in the universe than there are grains of sand on the whole planet! Is this correct? If that were true just how many planets and moons would we be talking about?
If the universe is flat then yes, that's true. If it's not true then it might still be true, I don't know.
« Last Edit: 18/10/2015 04:15:35 by chiralSPO »

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#### The Naked Scientists Forum

##### Re: Are there more stars in the Universe than grains of sand on Earth?
« Reply #4 on: 18/10/2015 00:11:23 »