Friday, February 17, 2006
Definition: The measure of time on which the calendar is based. It is the time taken for the earth to complete one orbit of the sun. The calendar year consists of an average of 365.25 mean solar days - three successive years of 365 days followed by one (leap) year of 366 years. The solar year (or astronomical year) is the average interval between two successive returns of the sun to the first point of Aries; it is 365.242 mean solar days. The sidereal year is the average period of revolution of the earth with respect to the fixed stars; it is 265.256 mean solar days. The anomalistic year is the average interval between successive perihelions; it is 365.259 mean solar days.