Convert Sidereal Months to Fortnights
Convert Sidereal Months (sid.mo) to Fortnights (fn) instantly and accurately.
Conversion Formula
fn = sid.mo × 1.951547264
About Sidereal Months
The sidereal month = Moon's orbital period relative to the fixed stars = 27.3217 days = 2,360,591.6 s - the shortest lunar month. It is ~2.21 days shorter than the synodic month (29.53 d) because Earth advances ~27° along its orbit in the same period; the Moon must travel further to re-align with the Sun. Used in GPS orbit design, tidal modelling, and lunar laser ranging. 1 sid.mo = 27.3217 d.
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 Months (sid.mo) | Fortnights (fn) |
|---|---|
| 1 sid.mo | 1.95155 fn |
| 2 sid.mo | 3.90309 fn |
| 5 sid.mo | 9.75774 fn |
| 10 sid.mo | 19.5155 fn |
| 25 sid.mo | 48.7887 fn |
| 50 sid.mo | 97.5774 fn |
| 100 sid.mo | 195.155 fn |