Every sun and moon figure on this site is calculated, not looked up. There is no database of sunrise times behind the scenes and no weather service supplying them. That has a consequence worth stating plainly: the numbers are only as good as the model that produces them, so this page sets out exactly what that model does, what it assumes, and where it stops being reliable.
Sunrise, sunset, solar noon, twilight and golden hour are computed with SunCalc, a well-established open-source implementation of the standard solar position formulae. It takes three inputs — a latitude, a longitude and a date — and returns the moments at which the sun crosses a set of defined altitudes. Nothing else is involved. The same maths runs whether you are looking at London or at a point in the middle of the Pacific, and it works for any date, past or future.
Because the calculation is purely geometric, it does not need a network connection to produce an answer, and it cannot go stale. What it also cannot do is know anything about your surroundings — which is the single biggest source of difference between what this site says and what you see out of the window. More on that below.
This matters more than it sounds, because different sources answer it differently. Here, sunrise is the moment the upper edge of the sun's disc first appears above a flat, unobstructed horizon, and sunset is the moment that same upper edge disappears. In the model this corresponds to a solar altitude of about −0.833°: roughly 0.27° for the radius of the sun's disc, plus about 0.57° for the standard atmospheric refraction that bends light over the horizon.
That refraction term is why the sun is already fully visible when, geometrically, it is still below the horizon. It is also why the day is never exactly twelve hours long at the equinox. Measuring from the disc's edge rather than its centre adds a couple of minutes at each end, refraction adds a few more, and the further you are from the equator the more the effect is stretched by the shallow angle at which the sun meets the horizon. At the latitude of Denmark or southern Britain the equinox day runs closer to twelve hours and nine minutes than to twelve hours flat.
Sunset is not darkness. The site reports three twilight thresholds, all defined by how far the sun's centre has sunk below the horizon:
The golden hour times use a different threshold again: the period when the sun sits below about 6° above the horizon, when the light is low, warm and heavily diffused. How long any of these last depends strongly on latitude — a tropical dusk is a matter of twenty minutes, while a Scandinavian summer never reaches astronomical darkness at all. Our page on when it gets dark goes through this in more detail.
Every time on the site is shown in the local clock time of the place you are asking about, not your own. The timezone is derived from the coordinates themselves using tz-lookup, which resolves a latitude and longitude to an IANA timezone identifier, and the conversion is then handled by the IANA timezone database. Daylight saving transitions are therefore applied automatically and historically correctly — including for past dates, when a country may have observed different rules than it does now. Our page on daylight saving time covers what the clock change does and does not do to the amount of daylight.
Above the Arctic Circle and below the Antarctic Circle there are dates with no sunrise and no sunset at all, because the sun never crosses the horizon in either direction. The model returns no valid time for those days, and rather than print something meaningless the site checks the sun's altitude at solar noon: if the sun is above the horizon at its highest point, the day is labelled midnight sun; if it is below, polar night. Day length for those dates is reported as 24 hours or 0 hours accordingly. Cities such as Tromsø, Murmansk and Utqiaġvik will show this for part of the year.
UV is the one figure on the site that is not calculated locally, because it depends on the state of the atmosphere rather than on geometry alone. Those values come from the Open-Meteo air quality API, hour by hour, and are cached briefly to avoid re-requesting the same location repeatedly. Two series are shown: the forecast UV index, which accounts for cloud cover, and a clear-sky figure drawn as a dashed outline — what the radiation would reach if the clouds broke. The gap between the two lines is the margin by which a cloudy forecast can still burn you.
Place-name search and reverse geocoding use the LocationIQ API. If you allow it, your browser's own Geolocation API is used instead, which is more precise; if you do not, a rough IP-based lookup is available as a fallback. Whichever route you use, the coordinates are what drive the calculation — the place name is only a label.
For a flat, open horizon at sea level, the computed times are accurate to within a minute or so. The realistic sources of error are all environmental rather than mathematical:
What this means in practice: treat the times as accurate to the minute for planning, and expect the horizon in front of you to have the final word.
Pages that quote today's figures are regenerated on a schedule — hourly for the sun and UV pages — so a page you load is at most an hour old. The interactive calculators recompute in your browser the moment you change the date or the location, so those are always current. Search engine snippets, by contrast, can be several days stale, which is why we deliberately keep dates and clock times out of page titles and meta descriptions.
If a figure on this site looks wrong, we would like to know — particularly for locations near a timezone boundary or above the Arctic Circle, where the edge cases live. Please tell us the place, the date and what you expected via the contact page. You can also read more about the project on our about page.