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Name: Doug A. Foster
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How do scientists measure the size of the other planets and their distances from the Earth?

Kepler, essentially, did it, and it was not simple. The idea is basically that if I know a planet's orbit around the Sun, and I know where the planet appears to be at two different positions of the Earth in the Earth's orbit, then I can figure the distance to the planet by triangulation. Once I know the distance, figuring the size is straight trigonometry based upon the planet's apparent size. It all checks, because the planet's distance from the Sun can be calculated from the length of its year.

J Lu

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