07 · Currency · Sun & civil twilight
Sun and civil twilight .
Sunrise, sunset, and civil-twilight beginning and end, for a latitude / longitude on a given date. The reference the night-currency rules in 14 CFR 61.57 are tied to.
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Section 01
Compute
Section 02
What civil twilight means
Civil twilight is the period between sunset (or before sunrise) when the centre of the sun's disc is between 0° and −6° below the horizon. There is enough light at the surface to make out terrain and to read instruments without artificial illumination, but the sun itself is below the horizon. Civil twilight ends in the evening when the sun reaches −6° and begins in the morning when it climbs back to −6°.
For US-rated pilots, the night-currency rule in 14 CFR 61.57(b) requires three takeoffs and landings in the preceding 90 days "during the period beginning 1 hour after sunset and ending 1 hour before sunrise" — a window that is partially inside civil twilight and partially after it. The same regulation also references "the period beginning 1 hour after sunset and ending 1 hour before sunrise" for logging night flight; this calculator gives you the four reference times you need to figure out either question on a given day.
The algorithm is the NOAA solar position algorithm (Spencer's Fourier series for the equation of time and declination, then standard hour-angle inversion). Accuracy is ±1 min at mid-latitudes for the current era; it degrades above ~66° latitude where the sun may not reach the relevant altitude on a given day, in which case the field shows "—".
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Common pitfalls
- 01All times are Zulu. The "your local time" line is your browser's local time, not the airport's — useful for sanity-check, not for the regulation.
- 02The night-currency rule (61.57) uses sunrise/sunset, not civil twilight. The logging-night-flight rule uses "end of evening civil twilight" / "beginning of morning civil twilight" — read the regulation carefully.
- 03The algorithm assumes a sea-level horizon. A field surrounded by mountains will have a shorter visible-sun day; the algorithm cannot model terrain.
- 04Above ~66° latitude (Arctic Circle), the sun may not rise or set on a given day. The calculator returns dashes for the times the sun never crosses the relevant altitude.
- 05Don't use this output for navigation or for fixing the start of a tactical operation — it's a planning aid, accurate to ±1–2 minutes. The official source is the US Naval Observatory.
Download
Free on the App Store. iOS 18 and up.
In the iOS app, sun and civil twilight are computed for each watched airport using its lat/lon — visible on the station detail screen as the day shortens.