Convert Sidereal Months to Tropical Years
Convert Sidereal Months (sid.mo) to Tropical Years (a_trop) instantly and accurately.
Conversion Formula
a_trop = sid.mo × 0.07480423247
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 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.
Quick Reference Table
| Sidereal Months (sid.mo) | Tropical Years (a_trop) |
|---|---|
| 1 sid.mo | 0.0748042 a_trop |
| 2 sid.mo | 0.149608 a_trop |
| 5 sid.mo | 0.374021 a_trop |
| 10 sid.mo | 0.748042 a_trop |
| 25 sid.mo | 1.87011 a_trop |
| 50 sid.mo | 3.74021 a_trop |
| 100 sid.mo | 7.48042 a_trop |