Methodology
How the times are calculated
Definitions
Every window here is defined by the sun’s altitude — its angle above (or below) the horizon. We compute the moment the sun crosses each threshold for your exact coordinates and date.
| Phase | Sun altitude | Meaning |
|---|---|---|
| Golden hour | −4° to +6° | Warm, low, directional light around sunrise/sunset. |
| Blue hour | −6° to −4° | Even, cool twilight just before sunrise / after sunset. |
| Sunrise / sunset | −0.833° | Sun’s upper limb at the horizon (incl. refraction). |
| Civil twilight | −6° | Bright enough for most outdoor activity. |
| Nautical twilight | −12° | Horizon still discernible at sea. |
| Astronomical twilight | −18° | Sky fully dark; faintest stars visible. |
Golden hour and blue hour tile the twilight cleanly: in the morning, blue hour runs from civil dawn (−6°) up to −4°, then golden hour from −4° through +6°; the evening mirrors this. We locate the −4° boundary by scanning the sun’s altitude and refining to sub-second precision.
Data & model
Sun and moon positions are computed in your browser using suncalc, a well-established implementation of standard astronomical algorithms (after Jean Meeus). Local times are rendered in each location’s IANA timezone, with all calculations performed on absolute UTC instants so daylight-saving transitions are handled correctly. No third-party API is used for sun or moon data; ISS passes use live orbital elements (TLE) from Celestrak with SGP4 propagation.
Accuracy & limitations
- • Times are typically accurate to within a minute for a flat, sea-level horizon.
- • We assume an ideal flat horizon. Mountains, buildings or a high vantage point shift real sunrise/sunset by minutes — sometimes more.
- • Atmospheric refraction is approximated with the standard −0.833° value; unusual temperature or pressure can vary it.
- • Elevation above sea level makes the sun rise slightly earlier and set later than shown.
- • Moon phase names use the nearest principal phase only near the exact instant; between, the moon reads as a waxing/waning crescent or gibbous.
For critical timing — a planned shot at the exact moment of sunset behind a ridge — treat these times as a close estimate and verify on location.