Kepler's Second Law:
II. The line joining the planet to the Sun sweeps out equal areas in
equal times as the planet travels around the ellipse.
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Kepler's Third Law:
III. The ratio of the squares of the revolutionary periods for two
planets is equal to the ratio of the cubes of their semi-major axes:
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With a bit of algebra, it can be expressed in years or distance:
To calculate the "radius" of Mars orbit (semi-major axis) from the orbital period: Mars orbits the Sun in 1.88 Earth years: