Animation illustrating Kepler's second law. Because the area mapped out by a planet over time does not change, it moves faster along its orbit when it is closer to its star. The Sun is shown at a fixed point, with a planet orbiting it along an elliptical orbit. The planet's position along its orbital path is shown at fixed time intervals, and for each interval the area defined by the position of the planet at present and at one time step previous and by the Sun (rather like a triangular pizza slice) is highlighted.
[NMSU, N. Vogt]