World time zones

Why time zones?

The Earth turns once on its axis in 24 hours, 15 degrees of longitude an hour. Noon, when the sun is highest, does not happen at the same moment everywhere: it comes one hour earlier for every 15 degrees east.

Until the 19th century, every town lived on its own solar time. Railways made that patchwork unworkable: British railway companies adopted Greenwich time in the 1840s, American ones a system of time zones in 1883. The following year, the International Meridian Conference in Washington chose the Greenwich meridian as the origin of longitude. The division into 24 one-hour zones, championed by the Canadian engineer Sandford Fleming, was then adopted country by country until the mid-20th century.

In practice, time zones follow borders more than meridians. Each country chooses its legal time, often for political or economic reasons. All time zones are defined by their offset from UTC.

Half-hour and quarter-hour offsets

Some countries chose an offset that is not a whole number of hours, to stay close to solar time: India and Sri Lanka (UTC+5:30), Iran (UTC+3:30), Afghanistan (UTC+4:30), Myanmar (UTC+6:30), central Australia (UTC+9:30 in Darwin), Newfoundland in Canada (UTC−3:30 right now) and the Marquesas Islands in French Polynesia (UTC−9:30).

Two places go down to the quarter hour: Nepal (UTC+5:45) and New Zealand’s Chatham Islands (UTC+13:45 right now).

A single time zone for all of China

China spans the equivalent of five time zones but has lived entirely on Beijing time (UTC+8) since 1949. In Kashgar, in the far west, the sun is highest around 15:00. In Xinjiang, part of the population follows an unofficial local time two hours earlier: in Ürümqi, timetables are sometimes shown in one or the other. The reference time zone database, and so this site, uses Xinjiang time for Ürümqi.

Spain on Berlin time

Madrid lies west of the Greenwich meridian, yet Spain has been on Central European Time, like Paris and Berlin, since Franco aligned it in 1940. The sun rises and sets late there, which partly explains Spanish hours. The Canary Islands are one hour behind mainland Spain.

The International Date Line

Opposite Greenwich, around the 180th meridian, runs the International Date Line: crossing it westwards you gain a day; eastwards you live the previous day again. It zigzags so as not to split archipelagos in two.

Kiribati moved it in 1995 so that the whole country would be on the same day: its Line Islands have since been on UTC+14, the furthest-ahead offset in the world, while the uninhabited Baker and Howland Islands are on UTC−12. Samoa switched sides at the end of 2011 to be closer to Australia and New Zealand: Friday 30 December 2011 never happened there. Today, Apia is on UTC+13.

Daylight saving time, north and south

Some countries put their clocks forward during their summer to make the most of evening light: Europe and North America from March to October or November, south-eastern Australia, New Zealand and Chile from October to March or April, since the seasons are reversed. The time difference between London and Sydney therefore varies by two hours over the year.

Most countries in Africa and Asia do not change their clocks, and several have recently given it up: Brazil in 2019, Iran in 2022, Morocco in 2026 (all changes since 2015). Daylight saving time dates around the world