Convert Sidereal Years to Draconic Months
Convert Sidereal Years (a_sid) to Draconic Months (drac.mo) instantly and accurately.
Conversion Formula
drac.mo = a_sid × 13.4225125
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 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
| Sidereal Years (a_sid) | Draconic Months (drac.mo) |
|---|---|
| 1 a_sid | 13.4225 drac.mo |
| 2 a_sid | 26.845 drac.mo |
| 5 a_sid | 67.1126 drac.mo |
| 10 a_sid | 134.225 drac.mo |
| 25 a_sid | 335.563 drac.mo |
| 50 a_sid | 671.126 drac.mo |
| 100 a_sid | 1342.25 drac.mo |