Skip to Main Content
Kinematical observations of the solar system have attained an accuracy reached in few other areas of measurement. The adequate description of these observations requires an elaborate and accurate terminology. This paper defines and discusses most of the important terms, coordinate systems, and methods of time reckoning which are used by astronomers in describing the motion of the solar system. No previous background in astronomy on the part of the reader is required. Warning is also given concerning terms whose meanings look obvious, but which in fact do not mean what they seem to.