Clock time and sun time

Ask most people when the sun is highest in the sky and they will say noon, twelve o'clock. In almost every city in the world that is not quite true, and in some it is wrong by two hours or more. The reason is simple: the clock follows an agreement, and the sun follows the map.

How to work it out for any place

The Earth turns through 360 degrees in 24 hours, which is 15 degrees in an hour, or one degree every four minutes. Take the longitude of a place and multiply by four: that is how many minutes its sun runs ahead of Greenwich (for places to the east) or behind it (to the west). Compare that with the place's official offset from UTC. The difference is how far the clock runs ahead of or behind the sun.

Take Mumbai. It lies at about 72.9° east, and 72.9 times 4 is about 292 minutes, or 4 hours 52 minutes. Indian Standard Time is UTC+5:30. So the clock in Mumbai runs about 38 minutes ahead of the sun, and the sun is highest at about 12:38 pm. In Kolkata, far to the east at about 88.4°, the same sum gives a clock 24 minutes behind the sun, and the sun is highest at about 11:36 am. One country, one clock, and more than an hour between the two cities by the sun.

Cities where the clock runs farthest ahead of the sun

These are the zone areas in our data whose largest city has half a million people or more and where standard time is most ahead of sun-time. Where summer time is used, add another hour in summer.

Cities where the clock runs farthest behind the sun

Here the sun is up, and down, early by the clock.

Cities where clock and sun nearly agree

For comparison, these large cities sit almost exactly on the line their time zone is built around.

Why countries accept the gap

A country gains a great deal from having one clock, or a clock shared with its neighbours and trading partners. A wide country that keeps a single time, as India and China do, must be ahead of the sun at one end and behind it at the other. Others choose a clock well ahead of the sun on purpose, because light evenings are popular. Summer time is the same idea applied for half the year.

The small print

The times above are averages. Because the Earth's path round the sun is an oval and its axis is tilted, the true moment when the sun is highest drifts through the year, up to about a quarter of an hour either side of the average. The tables use the longitude of the largest city of each zone area from GeoNames and its standard (winter) offset from the IANA time zone database. Every place page on this site shows the same sum for its own largest city.