Animation of Orbits

I have created several animations that show a planet orbiting its parent star, and illustrating the gravitationnaly induced wobble on the star, for some of the stars known to have such companions.

Indeed both objects (the star and the planet) follow an orbit that is an ellipse (Kepler's first law), whose focus is at the center of gravity of the system.

If the planet is massive enough, the center of gravity of the system is displaced from the center of the star by enough to cause a measurable wobble of the star. It is this wobble that can be detected in the Doppler shift of the light coming from the star. The light reflected by the planet itself is at least 10,000 fainter that the light from the star and currently cannot be directly detected.

From the Doppler shift, we can compute the radial velocity of the star as depicted in the graph. when the star wobbles towards us, the star light is blue shifted (slightly shorter wavelength), while when the star wobbles away from us, its light is read shifted (slightly longer wavelength).

These animations are available in several formats. Depending on your bandwidth, browser, and hardware capabilities, one format might be better that the others.

16 Cygnus B (16CygB)

16 Cygnis B has a highly eccentric orbit:

Rho Coronae Borealis (rhoCrB)

Rho Coronae Borealis has a nearly circular orbit:


Sylvain G. Korzennik  (
Last modified: Tue Aug 24 16:13:16 1999