Methodology

Lightphase is only useful if you trust the times. Here is exactly what it computes, and where it deliberately disagrees with other tools.

The six phases

Every phase is a band of solar elevation — the angle between the horizon and the centre of the sun. Six thresholds divide the sky: −18°, −12°, −6°, 0°, +6° and +35°. That is the whole model. Nothing else feeds it.

Night and Daylight are not phases so much as the two ends of the day — the light before anything starts and after everything has finished. They are shown because the sun has to be somewhere.

What direction changes

The same threshold means different things going up and coming down. At +6° in the morning the sun is entering the 35° Window; at +6° in the evening it is entering Golden Hour. Lightphase reads the direction of travel as well as the angle, which is why morning and evening are listed separately.

Why Blue Hour is not here

Because it overlaps. Blue Hour, as most tools define it, sits inside what Lightphase calls Nautical and Civil Twilight, and different tools draw it at different angles. Mixing two systems would make every boundary approximate. Lightphase implements one model exactly rather than several loosely, so the deep blue window you are looking for is the back half of Nautical Twilight and the front of Civil.

Why sunrise looks late

Lightphase puts sunrise at the moment the sun’s centre crosses 0° geometrically. Almanacs, weather apps and most photography tools put it at −0.833° — the moment the sun’s upper edge appears, allowing for the way the atmosphere bends light near the horizon and lifts the disc into view before it is really there.

So Lightphase’s sunrise runs three to five minutes after a published one, and its sunset the same interval before. That is not an error — it is the price of one consistent definition. The twilight thresholds are geometric in every system, so those times match published tables to within a minute.

Lightphase also assumes a flat, sea-level horizon. It does not know about the mountain in front of you, or that you are standing on top of one — real elevation moves first light earlier by several minutes.

How the times are found

Solar position is deterministic: given a date, a time and a pair of coordinates, there is exactly one right answer. Lightphase computes it in your browser from the standard astronomical series, then finds each crossing by sweeping the day minute by minute, bracketing every point where the sun passes a threshold, and narrowing to the second.

That is slower than the closed-form formula a solar library would use, and it buys three things. It handles all six thresholds by one method, including +35°, which no rise-and-set formula exposes. It needs no special case at the poles: if the sun never reaches a threshold, no crossing is reported and none is invented. And where the sun grazes a threshold and falls back — which is what happens above the Arctic Circle in midsummer — it correctly finds both sides.

The engine is checked against an independent implementation of the NOAA solar equations, which arrives at elevation by a different route. Across nine locations, five dates and every hour of the day, the two agree to within a hundredth of a degree — about two and a half seconds of the sun’s motion.

Time zones

“Today” means the local calendar day where you are, resolved through your device’s time zone. Never a fixed offset from UTC — that would quietly shift every phase time by an hour on the two days a year the clocks change. Days that are 23 or 25 hours long are handled as such.

Your location

Your coordinates are read once, held in memory, and used for the calculation on your device. They are not sent anywhere, not stored, and not attached to anything. The privacy page is short and specific.