Convert Days to Sidereal Years
Convert Days (d) to Sidereal Years (a_sid) instantly and accurately.
Conversion Formula
a_sid = d × 0.002737803092
About Days
A day (d) = exactly 86,400 s. Earth's actual solar day varies ±16 s due to orbital eccentricity and axial tilt (equation of time). Leap seconds (abandoned in UTC after 2035) corrected the TAI-UT1 divergence. Mars's sol = 24 h 39 min 35 s ≈ 88,775 s; a Martian year = 668.6 sols. The day structures circadian biology, tides, and planetary science. 1 day = 86,400 s = 24 h.
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
| Days (d) | Sidereal Years (a_sid) |
|---|---|
| 1 d | 0.0027378 a_sid |
| 2 d | 0.00547561 a_sid |
| 5 d | 0.013689 a_sid |
| 10 d | 0.027378 a_sid |
| 25 d | 0.0684451 a_sid |
| 50 d | 0.13689 a_sid |
| 100 d | 0.27378 a_sid |