The branch of astronomy that deals with the motions of bodies in orbit, such as planets, natural and artificial satellites, space probes, comets, and binary or multiple stars. The forces involved are gravitation and, for some artificial satellites, atmospheric drag and radiation pressure from sunlight. Although in most cases the orbit of a body is nominally elliptical and subject to Kepler's laws, the attraction of other bodies and the presence of other forces will cause small departures, known as perturbations, from the elliptical form. See alson-body problem; three-body problem.
Subjects: astronomy and cosmology.