出典:Wikipedia
出典:『Wikipedia』 (2011/02/09 03:18 UTC 版)
A sidereal year is the time taken by the Earth to orbit the Sun once with respect to the fixed stars. Hence it is also the time taken for the Sun to return to the same position with respect to the fixed stars after apparently travelling once around the ecliptic. It was equal to 365.256363004 days at noon 1 January 2000 (J2000.0). This is 20m24.5128s longer than the mean tropical year at J2000.0. The word "sidereal" is derived from the Latin sidus meaning "star".