Kepler's laws of planetary motion law" is what became the Second Law in the set of three; but Kepler did himself not privilege it in that way. Johannes Kepler published his first two laws about planetary motion in 1609, having found them by analyzing the astronomical observations of Tycho Brahe. Kepler's third law was published in 1619. Kepler had believed in the Copernican model of the solar system, which called for circular orbits, but he could not reconcile Brahe's highly precise observations with a circular fit to Mars' orbit—Mars coincidentally having the highest eccentricity of all planets except Mercury. His first law reflected this discovery.
Stellar dynamics stellar system. Given the large number of objects in a stellar system, stellar dynamics is usually concerned with the more global, statistical properties of several orbits rather than with the specific data on the positions and velocities of individual orbits. The motions of stars in a galaxy or in a globular cluster are principally determined by the average distribution of the other, distant stars. Stellar encounters involve processes such as relaxation, mass segregation, tidal forces, and dynamical friction that influence the trajectories of the system's members. Stellar dynamics also has connections to the field of plasma physics. The two fields