Solar Noon Is Not Twelve O'Clock

Four minutes per degree, and a zone fifteen degrees wide

The Earth turns 360 degrees in 24 hours, which is 15 degrees an hour or one degree every four minutes. Time zones are drawn as hour-wide bands, so a zone that behaved itself would be fifteen degrees across and no place inside it would be more than half an hour from the clock. Political borders do not behave. Spain sits mostly west of Greenwich but keeps central European time, so Vigo's solar noon is 14:37 while Barcelona's, in the same country and on the same clock, is 13:53 — forty-four minutes of daylight bookkeeping between two Spanish cities.

Widen the frame to the whole of central European summer time — Brest in the west, Warsaw in the east — and the spread reaches one hour forty-two. That is why a Breton June evening keeps light until half past ten while a Warsaw one is dark by ten, even though both clocks read the same. Nothing about the sun differs; the label on the hour does.

The tool asks for a UTC offset, not for a country — and that is deliberate

Give the calculator a latitude, a longitude, a date and a UTC offset and it returns sunrise, sunset, solar noon and day length. It does not know about summer time, and it says so: the times it prints are for the offset you chose, so if your country is on daylight saving that day, add an hour. This is the honest arrangement rather than a limitation. A tool that guessed your daylight rule from a country name would be wrong at the edges — Portugal and mainland Spain share a border and not an offset, and the Canaries share a country with neither.

The sunrise and sunset it returns use the conventional −0.833° horizon: sunrise is the moment the sun's upper edge appears, which is a few minutes before its centre reaches the geometric horizon, because the atmosphere bends the light and the disc has a radius of its own. That is the same definition every national almanac uses, so the figures are comparable with an official table — and, like an official table, they assume a flat sea horizon rather than the hill behind your house.

Day length: latitude does everything

Longitude moves the times; latitude sets how long the day is. On 21 June 2026 the day runs 12 h 08 at Quito, 13 h 45 at Miami, 14 h 53 at Lisbon, 16 h 11 at Paris, 16 h 50 at Berlin and 21 h 09 at Reykjavík — and at Tromsø the sun does not set at all. Six months later the same list reads 12 h 07, 10 h 32, 9 h 27, 8 h 15, 7 h 39 and 4 h 07, with Tromsø in polar night. The equator barely notices the year; the Arctic lives by it.

The rate of change is just as uneven across the year as it is across the map. At the latitude of Paris the day gains or loses about 3.6 minutes every 24 hours at the equinoxes and essentially nothing at the solstices. That is why the difference between one March morning and the next is obvious and the difference between two June mornings is not: the equinox is where the clock is moving fastest, not the solstice.

Where the sun refuses to set, and why it starts below the Arctic Circle

The textbook line is the Arctic Circle at 66.56° N, the latitude where the sun geometrically stays up for one whole day a year. Run the shipped calculation and midnight sun turns up further south than that: at 66.0° N it already lasts about a fortnight. The reason is the same −0.833° horizon that shifts every sunrise — refraction and the sun's own radius keep the disc technically visible when its centre is already below the geometric horizon, so the midnight sun starts roughly half a degree of latitude early.

The same effect makes the two polar phenomena asymmetric. At 66.0° N there are already days of midnight sun and not one single day of polar night, because refraction lifts the sun into view in December just as it keeps it in view in June. Polar night, properly defined, therefore begins a degree or so further north than midnight sun does. When the calculator prints its polar-day or polar-night banner instead of two times, it is not giving up — it is telling you the honest answer to a question with no sunrise in it.

Frequently asked questions

Why does the sun set so late in western France and western Spain?

Because both keep central European time while sitting west of the meridian that time is built on. Brest is 4.5 degrees west of Greenwich and runs on UTC+2 in summer, which puts its solar noon at 14:20 and its June sunset at 22:23. Vigo, further west still, sets at 22:15 with solar noon at 14:37. The sun is behaving normally; the clock is two hours ahead of the sky.

Is the sunrise time I get the same as the one in a national almanac?

To within a minute or so, yes, provided you enter the same coordinates and remember summer time. Both use the −0.833° horizon convention. Larger differences usually mean one of three things: an almanac quoting a whole city while you entered a precise point, a daylight-saving hour missing on one side, or a local horizon — mountains, a coastal cliff, a high-rise — that no latitude-only model can see.

How long is the longest day where I live?

Enter your latitude and the June solstice date — the tool returns it directly. As a rough guide for the northern hemisphere: about 12 h at the equator, 13 h 45 at 26° N, 14 h 53 at 39° N, 16 h 11 at 49° N, 16 h 50 at 53° N, 21 h 09 at 64° N, and continuous daylight above roughly 66° N. Your longitude does not change the length at all, only the clock times at which it starts and ends.