Convert Fortnights to Sidereal Days
Convert Fortnights (fn) to Sidereal Days (sid.d) instantly and accurately.
Conversion Formula
sid.d = fn × 14.03833074
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 Days
A sidereal day = Earth's rotation period relative to the stars = 23 h 56 min 4.0905 s = 86,164.0905 s - ~3 min 56 s shorter than the 24 h solar day because Earth advances ~1° in its orbit each day. Equatorial telescope mounts rotate at one turn per sidereal day to track stars. VLBI, GPS orbit determination, and polar-motion monitoring use sidereal rotation as their reference. 1 sid. day = 86,164.0905 s.
Quick Reference Table
| Fortnights (fn) | Sidereal Days (sid.d) |
|---|---|
| 1 fn | 14.0383 sid.d |
| 2 fn | 28.0767 sid.d |
| 5 fn | 70.1917 sid.d |
| 10 fn | 140.383 sid.d |
| 25 fn | 350.958 sid.d |
| 50 fn | 701.917 sid.d |
| 100 fn | 1403.83 sid.d |