Year
Symbol: a (Latin for anus = Year) or y
One year is the period of time taken by a planet to orbit his star.
The sidereal year is the time taken for the Earth to complete one revolution of its orbit, as measured against a fixed frame of reference (such as the fixed stars, Latin sidera, singular sidus). Its duration in SI days of 86400 SI seconds each is on average:
365.256363051 days (365 d 6 h 9 min 9.7676 s) (at the epoch J2000.0 = 2000 January 1 12:00:00 TT).
1a = 31,558,149.5s
1s = 0.00000003168753a