Convert Tropical Years to Sidereal Years
Convert Tropical Years (a_trop) to Sidereal Years (a_sid) instantly and accurately.
Conversion Formula
a_sid = a_trop × 0.9999611971
About Tropical Years
The tropical year = time from March equinox to the next = 365.24219 days = 31,556,925.2 s - the year that governs the seasons. The Gregorian 97/400 leap rule approximates it as 365.2425 days, leaving a residual drift of only ~26.8 s/year. The tropical year shortens ~0.53 s per century due to tidal deceleration. Persian Solar Hijri and Mayan Haab' calendars also approximate it. 1 a_trop ≈ 365.24219 d.
About Sidereal Years
The sidereal year = Earth's orbital period relative to the stars = 365.25636 days = 31,558,149.8 s - about 20 min 24 s longer than the tropical year. The gap arises from precession of the equinoxes (~50 arcsec/year westward drift), which causes the tropical year to end slightly before the sidereal orbit completes. JPL DE440 ephemerides and J2000.0 epoch are anchored to the sidereal frame. 1 a_sid = 365.25636 d.
Quick Reference Table
| Tropical Years (a_trop) | Sidereal Years (a_sid) |
|---|---|
| 1 a_trop | 0.999961 a_sid |
| 2 a_trop | 1.99992 a_sid |
| 5 a_trop | 4.99981 a_sid |
| 10 a_trop | 9.99961 a_sid |
| 25 a_trop | 24.999 a_sid |
| 50 a_trop | 49.9981 a_sid |
| 100 a_trop | 99.9961 a_sid |