. . . . and the Discovery of Planets

in a two-body, planet-star system, the planet does
not orbit the star;

rather, both planet and star orbit a common point,
the system's center of mass, CM

imagine a system composed of a Jupiter-size planet
and a star the size of our Sun

if the planet, like Jupiter, were some 480 million
miles from the star; then both the planet and the
star would orbit around a single point, the CM,
located 28 thousand miles above the star's surface

given that the star's mass is approximately 1,000
times greater than that of the planet, the radius of
its orbit would be close to 1,000 times less than the
planet's - approximately 462 thousand miles

both star and planet would take close to 12 years
to complete their orbits

seen from a distance, the star in this two-body
system would seem to "wobble" as it orbits the
system's center of mass;

and this wobbling could be detected by a distant
observer examining Doppler shifts in the star's
spectral lines

this examination of the blue shifting of the star's
spectral lines as its orbit takes it towards us, and
subsequent red shift as it recedes, is called the
wobble method of searching for planets

the wobble method has led to the discovery of
more than 200 planets; it is described in greater
detail in the video below



the above is an excerpt from the History Channel's
Universe series