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Physics, Astronomy & Cosmology / Re: Are there more stars in the Universe than grains of sand on Earth?
« 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.
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.