Convert Tropical Years to Draconic Months
Convert Tropical Years (a_trop) to Draconic Months (drac.mo) instantly and accurately.
Conversion Formula
drac.mo = a_trop × 13.42199166
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 Draconic Months
The draconic (nodical) month = 27.2122 days = 2,351,135.8 s - the interval between successive Moon passages through the same orbital node. Named from the Latin 'draco' (dragon): eclipses only occur near the nodes, where the Moon can align with the Sun or Earth's shadow. The Saros cycle (18 yr 11 d) equals ~242 draconic months, enabling eclipse sequence forecasting. 1 drac.mo = 27.2122 d.
Quick Reference Table
| Tropical Years (a_trop) | Draconic Months (drac.mo) |
|---|---|
| 1 a_trop | 13.422 drac.mo |
| 2 a_trop | 26.844 drac.mo |
| 5 a_trop | 67.11 drac.mo |
| 10 a_trop | 134.22 drac.mo |
| 25 a_trop | 335.55 drac.mo |
| 50 a_trop | 671.1 drac.mo |
| 100 a_trop | 1342.2 drac.mo |