Convert Sidereal Years to Millennia
Convert Sidereal Years (a_sid) to Millennia (ka) instantly and accurately.
Conversion Formula
ka = a_sid × 0.001000037956
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 Millennia
A millennium (1 ka) = 1,000 Gregorian years ≈ 3.156 × 10¹⁰ s. Standard unit in archaeology and Quaternary geology: Neolithic transition ~10-12 ka BP; Last Glacial Maximum ~21 ka BP; Homo sapiens leaving Africa ~60-70 ka BP. Milankovitch cycles include the 41 ka obliquity and ~100 ka eccentricity cycle. EPICA Antarctic ice core spans ~800 ka. Precession completes ~26 ka. 1 ka = 1,000 yr.
Quick Reference Table
| Sidereal Years (a_sid) | Millennia (ka) |
|---|---|
| 1 a_sid | 0.00100004 ka |
| 2 a_sid | 0.00200008 ka |
| 5 a_sid | 0.00500019 ka |
| 10 a_sid | 0.0100004 ka |
| 25 a_sid | 0.0250009 ka |
| 50 a_sid | 0.0500019 ka |
| 100 a_sid | 0.100004 ka |