The period of a planet orbiting a round a star, for example, the Sun, relates to th=e radius of the orbit according to the third Kepler's Law:

`T^2 = (4pi^2)/(GM) a^3`

Here, T is the period of the planet ( 1year for the Earth orbiting the Sun), M is the mass of the Sun,...

(The entire section contains 153 words.)

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