orbiting around a common barycenter. The sizes, and this particular type of orbit are similar to the Pluto-Charon system.]]In physics, an orbit is the path that an object makes around another object while under the influence of a central force, such as gravity.
History
Orbits were first analyzed mathematically by Johannes Kepler who formulated his results in his three laws of planetary motion. First, he found that the orbits of the planets in our solar system are elliptical, not circular (or epicyclic), as had previously been believed, and that the sun is not located at the center of the orbits, but rather at one focus. Second, he found that the orbital speed of each planet is not constant, as had previously been thought, but rather that the speed of the planet depends on the planet's distance from the sun. And third, Kepler found a universal relationship between the orbital properties of all the planets orbiting the sun. For each planet, the cube of the planet's distance from t
Source:
http://en.wikipedia.org/wiki/Orbit