Kepler's Orbital Laws

Three laws that govern all planetary motion

Eccentricity e: 0.60 Speed: 1.0× Show equal areas Show radii

Periapsis

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Apoapsis

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Period T

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Current r

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Speed v

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T² / a³

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Law 1: Orbits are ellipses with the Sun at one focus. Law 2: A line from Sun to planet sweeps equal areas in equal times (shaded sectors). Law 3: T² ∝ a³ — the square of the period is proportional to the cube of the semi-major axis.