Functions:
The choice menu at bottom right allows the selection of the Earth, Jupiter, and several of the purported extrasolar planets.
'Start' and 'Stop'
begin and pause the simulation. 'Reset' returns the simulation to time=0.
'Orbits' highlights the elliptical orbit followed by the reported planet.
'Grid' shows a calibrated length scale (in [AU]) centered on the star.
'Faster' and 'Slower' change the time step in the simulation by a factor of two, and
'Labels' attaches text labels to the star and planet.
The sliders show the system's parameters: the planet's mass (in [M_Jupiter]),
the star's mass (in [M_sun]), and the semimajor axis (in [AU]) and eccentricity of the planet's orbit.
The screen shows the orbital period (in [yrs]), the elapsed time (in [yrs]), the star-planet separation (in [AU]) and the x and y components of the star's velocity, which would be observed as a Doppler effect.
Designing Your Own:
You can use the scrollbars to design your own star-and-planet system, and see how properties such as the geometry and period change. (The choice window will black out, to indicate that you are not simulating a system from its list.)
The Simulation: The planet is started at greatest separation (aphelion) at time=0 and its motion is followed through an elliptical trajectory using a fixed time step, with orbital parameters taken either from stored data (for a real or reported planet) or from the scrollbars. The axes automatically rescale if the orbit takes the planet beyond the boundaries of the display area.
Reference