Convert Sidereal Years to Megayears
Convert Sidereal Years (a_sid) to Megayears (Ma) instantly and accurately.
Conversion Formula
Ma = a_sid × 1.000037956e-6
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 Megayears
A megayear (1 Ma) = 10⁶ yr ≈ 3.156 × 10¹³ s - the timescale of geology and tectonic evolution. The K-Pg mass extinction at 66.0 Ma; Cambrian explosion ~538.8 Ma; Great Oxygenation Event ~2,400 Ma. Plate motion at 2-10 cm/yr = 200-1,000 km per Ma (Atlantic ~3,000 km wider since Pangaea rifting ~200 Ma ago). Background extinction rate measured in extinctions per million species-years. 1 Ma = 10⁶ yr.
Quick Reference Table
| Sidereal Years (a_sid) | Megayears (Ma) |
|---|---|
| 1 a_sid | 1 × 10-6 Ma |
| 2 a_sid | 2 × 10-6 Ma |
| 5 a_sid | 5 × 10-6 Ma |
| 10 a_sid | 1 × 10-5 Ma |
| 25 a_sid | 2.5 × 10-5 Ma |
| 50 a_sid | 5 × 10-5 Ma |
| 100 a_sid | 0.000100004 Ma |