## KEPLER'S SECOND LAW

### Kepler's second law states that as a planet orbits the Sun, a line joining
the planet and the Sun sweeps out equal areas in equal times. As a result,
a planet must move faster in its orbit when it is near the Sun than when it
is far from the Sun. If the planet moves in a circular orbit so that its
distance from the Sun doesn't change, the planet's speed is constant. The more
elongated the orbit, the greater than variation in orbital speed.

The simple animation below shows this change in orbital speed. You can alter
the orbit shape by clicking on the buttons at the top of the blue region.
The buttons are labeled with the orbital "eccentricity," a measure of the
ellipticity of the orbit. Eccentricity = 0.0 corresponds to a circle. The
larger the eccentricity, the more elongated the orbit. An eccentricity =1.0
corresponds to an open orbit.

To stop the animation, click on the blue area. It takes a moment or two to stop running.

Choose an eccentricity (E) for the orbit by clicking a button below