"The number of habitable worlds in our galaxy is certainly in the tens of billions, minimum, and we haven't even talked about the moons. And the number of galaxies we can see, other than our own, is about 100 billion."

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There are in fact 100 billion galaxies, each of which contain something like a 100 billion stars. Think of how many stars, and planets, and kinds of life there may be in this vast and awesome universe.

— Carl Sagan