Convert Sidereal Years to Sidereal Months
Convert Sidereal Years (a_sid) to Sidereal Months (sid.mo) instantly and accurately.
Conversion Formula
sid.mo = a_sid × 13.36874628
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.
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.
Quick Reference Table
| Sidereal Years (a_sid) | Sidereal Months (sid.mo) |
|---|---|
| 1 a_sid | 13.3687 sid.mo |
| 2 a_sid | 26.7375 sid.mo |
| 5 a_sid | 66.8437 sid.mo |
| 10 a_sid | 133.687 sid.mo |
| 25 a_sid | 334.219 sid.mo |
| 50 a_sid | 668.437 sid.mo |
| 100 a_sid | 1336.87 sid.mo |