Description

This simulation illustrates three of Kepler's complete theory for planetary orbits. The planet shown orbits the Sun in an ellipse with the Sun at one focus (Kepler's First Law). The line from the Sun to the planet sweeps out equal areas in equal times (Kepler's Second Law). The square period of the planet's orbit is proportional to the cube of its semimajor axis (Kepler's Third Law). The top view shows the Sun, the orbit of the planet, the motion of the planet along its orbit, and the area swept out by the Sun-planet line. The lower view shows the apparent motion of the planet relative to the stars as seen from the Sun. There is also a plot showing the area swepts by the Sun-planet line as a function of time.

The user can adjust the semimajor axis (a) of the orbit, the eccentricity (e) of the orbit, and the longitude of aphelion (lonAp) for the orbit. Note that the simulation rescales when you change the semimajor axis, so it doesn't look like the orbit has changed size but it has (as will be apparent from the period of the orbit and the area plot). Controls let the user play, pause, step, reset, and initialize the simulation. The simulation also displays the time in years and the ratio of the area swept to the total area (A_s/A_t).