Since the time of Newton the basic structure of the solar system and the laws that govern the motions of the bodies within it have been well understood. One central body, the Sun, containing most of the mass of the system has a family of attendant planets in more-or-less circular orbits about it. In their turn some of the planets have accompanying satellites, including the Earth with its single satellite, the Moon. With improvements in telescope technology, and more recently through space research, knowledge of the solar system has grown apace. Since the time of Newton three planets have been discovered and also many additional satellites
