Planets travel along slightly flattened elliptical orbits rather than perfect circles. The Sun (the yellow dot) is not at the center of the ellipse, but at one of its foci. Remarkably, a planet moves faster when it is closer to the Sun and slower when it is farther away, yet it always sweeps out exactly the same area during the same amount of time. Press play and see it for yourself.
Kepler’s Second Law (law of equal areas): The area swept out by the line connecting the Sun and the planet is always the same over equal time intervals. So near the Sun (at perihelion), the planet moves quickly to sweep out the required area, while farther away (at aphelion), it can move more slowly and still sweep out the same area.
Orbital eccentricity (0 = circle; closer to 1 = more elongated)0.6
Current speed: -
💡 Thanks to this law, Newton was later able to explain perfectly “why these orbits occur” using the law of universal gravitation — Kepler discovered this rule purely from observational data.