Convert Fortnights to Sidereal Years
Convert Fortnights (fn) to Sidereal Years (a_sid) instantly and accurately.
Conversion Formula
a_sid = fn × 0.03832924329
About Fortnights
A fortnight = exactly 14 days = 2 weeks = 1,209,600 s. From Old English 'feowertiene niht' (fourteen nights), reflecting the Germanic custom of counting nights. Common in British, Irish, Australian, and NZ English for pay periods, rental cycles, and parliamentary recesses. The Moon's phase advances ~half a synodic month (≤14.77 days) per fortnight; spring and neap tides also cycle fortnightly. 1 fortnight = 14 d = 1,209,600 s.
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.
Quick Reference Table
| Fortnights (fn) | Sidereal Years (a_sid) |
|---|---|
| 1 fn | 0.0383292 a_sid |
| 2 fn | 0.0766585 a_sid |
| 5 fn | 0.191646 a_sid |
| 10 fn | 0.383292 a_sid |
| 25 fn | 0.958231 a_sid |
| 50 fn | 1.91646 a_sid |
| 100 fn | 3.83292 a_sid |