What counts as sunrise
Sunrise is the moment the upper edge of the sun first appears over a flat horizon, not the moment its centre arrives. The sun is about half a degree wide, so that difference alone is worth a minute or two.
The atmosphere bends light, which lifts the image of the sun by roughly 34 arcminutes near the horizon. The practical consequence is strange and true: at the moment you first see the sun rise, it is still geometrically below the horizon. We use the standard refraction figure of 34′ and a solar semidiameter of 16′, which together put sunrise at a sun centre 50′ below the horizon — the convention the US Naval Observatory uses.
We put the observer at sea level and ignore the height of the ground, exactly as USNO does. Elevation genuinely matters — from a mountain you see the sun earlier — but applying it needs the height of the horizon you are looking at, not the height of the ground under your feet, and nobody has that for every city.
Why our times can differ from another site by a minute
We round to the nearest minute. Several well-known sites cut the seconds off instead. On 22 October 2026 the sun sets over Berlin at 17:56:39: we print 17:57 and they print 17:56. Neither is a mistake, and the gap shows up on roughly half of all values.
We round because the authority rounds. Against the published USNO values, rounding matched every sunrise, sunset, twilight and solar noon we tested, to the minute.
Twilight, golden hour and blue hour
Civil twilight runs until the sun is 6° below the horizon, nautical twilight to 12° and astronomical twilight to 18°. Those are standard. Golden hour and blue hour are not: they are photographers’ conventions, and we use the common ones — golden hour while the sun is between 4° below and 6° above the horizon, blue hour between 6° and 4° below. Another site may draw those lines slightly differently and be just as right.
At high latitudes these simply stop happening. North of about 60° in June the sun never gets 18° below the horizon, so astronomical twilight does not exist that night. We say so rather than printing a time borrowed from another day.
The moon
A lit percentage is only meaningful with the instant it was computed for: it moves by up to ten points in a day. Every percentage on a page is for local noon of the date the page is about, in the header as well as in the body, so the two can never disagree. That is also why two reputable sites can show 83 % and 85 % for the same date and neither be wrong.
The four principal phases are instants, not days. A full moon is one moment for the whole planet, so the same full moon falls on different dates in New York and Berlin. Every phase time on this site carries its time zone for that reason.
What we check against
The engine is astronomy-engine, and the test suite pins it against published values from the US Naval Observatory: sunrise, sunset, all three twilights, solar noon, moonrise, moonset, illumination and polar day. Phase instants agree with USNO to within a minute. City coordinates and time zones come from GeoNames.
How fresh the page is
Pages are rebuilt every night. Between two rebuilds the times on a city page belong to the date printed under its heading; if you open a page on a later date, the page notices, takes the moving sun off the curve and says so, rather than pretending yesterday’s times are today’s.
