Convert Sidereal Days to Fortnights
Convert Sidereal Days (sid.d) to Fortnights (fn) instantly and accurately.
Conversion Formula
fn = sid.d × 0.07123354043
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.
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.
Quick Reference Table
| Sidereal Days (sid.d) | Fortnights (fn) |
|---|---|
| 1 sid.d | 0.0712335 fn |
| 2 sid.d | 0.142467 fn |
| 5 sid.d | 0.356168 fn |
| 10 sid.d | 0.712335 fn |
| 25 sid.d | 1.78084 fn |
| 50 sid.d | 3.56168 fn |
| 100 sid.d | 7.12335 fn |