Convert Sidereal Months to Sidereal Years
Convert Sidereal Months (sid.mo) to Sidereal Years (a_sid) instantly and accurately.
Conversion Formula
a_sid = sid.mo × 0.07480132985
About Sidereal Months
The sidereal month = Moon's orbital period relative to the fixed stars = 27.3217 days = 2,360,591.6 s - the shortest lunar month. It is ~2.21 days shorter than the synodic month (29.53 d) because Earth advances ~27° along its orbit in the same period; the Moon must travel further to re-align with the Sun. Used in GPS orbit design, tidal modelling, and lunar laser ranging. 1 sid.mo = 27.3217 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
| Sidereal Months (sid.mo) | Sidereal Years (a_sid) |
|---|---|
| 1 sid.mo | 0.0748013 a_sid |
| 2 sid.mo | 0.149603 a_sid |
| 5 sid.mo | 0.374007 a_sid |
| 10 sid.mo | 0.748013 a_sid |
| 25 sid.mo | 1.87003 a_sid |
| 50 sid.mo | 3.74007 a_sid |
| 100 sid.mo | 7.48013 a_sid |