The Laws of Planetary Motion
I. The orbits of the planets are ellipses, with the Sun at one focus of the ellipse.
II. The line joining the planet to the Sun sweeps out equal areas in equal times as the planet travels around the ellipse.
III. The ratio of the squares of the revolutionary periods for two planets is equal to the ratio of the cubes of their semimajor axes:
The eccentricity of the Earth‘s orbit is currently about 0.0167
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