Timezones overview

Overview of all current time zones

Americas

Europe

Africa

Asia

Australia

Indian Ocean

Pacific Ocean

Atlantic Ocean

Antarctica

Inconsistent and duplicate abbreviations

The abbreviations of the individual zones, such as "CST" or "CET", are often confusing. In fact, they are the result of regular use rather than standardization. The ISO 8601 standard specifies spellings and components of the international format, but these abbreviations do not appear there.

In fact, the abbreviations often used today are anything but clear or understandable. The abbreviation "AST" stands for both, the American Atlantic Standard Time and Arabia Standard Time. Other abbreviations such as AMT, CST, GFT, GST, ICT, IST and PST are also used more than once. The current use of these abbreviations therefore only makes sense if it is clear from the context which geographical region is being referred to. The term CST is widely used within the USA and makes sense in most cases, because using the clunky term "Central Standard Time" would be too cumbersome in the vast majority of cases anyway. However, it must be clear that it is not China Standard Time (13 hours ahead of Central Standard Time) or Cuba Standard Time (1 hour ahead).

The letter "S" often causes confusion. In Europe, the terms summer time and winter time have become established. Winter time is the standard time. As a result, some time zones refer to themselves as "summer time", others as "standard time". Both can be found with an "S" in the abbreviation. The abbreviation UYST, for example, stands for Uruguay Summer Time, but not for Uruguay Standard Time. In many other countries, summer time is called "daylight time" and is abbreviated with a "D". In many cases, the "S" or "D" is added to the 3-letter abbreviation of standard time (CET, CEST). However, even this spelling is not standardized. In other zones, the letters are simply exchanged (AST, ADT).

The abandonment of daylight saving time in many countries leads to a further complication. Time zones that no longer have daylight saving time sometimes sometimes dispense with the suffix "Standard". For example, Singapore Standard Time (SST) has now become Singapore Time (SGT). The first two letters were taken from the international 2-letter country abbreviation.

Time zone allocation

Since a day has 24 hours, the globe was divided into 24 equal theoretical parts, each extending from the North Pole to the South Pole. Each of these sections is 15 degrees of longitude wide and marks one hour. The zero longitude is the UTC0 zone time, while the 15th longitude is the UTC+1 time. Thus, in each of these optimized sections, the time is aligned optimally to the position of the sun, based on where the sun is highest at noon everywhere

Of course, this purely theoretical structure cannot be combined with national borders. The western parts of Mexico are actually in the UTC-7 time zone, but UTC-6 applies to the whole country. Numerous countries therefore opt for a uniform time zone within its own borders. For example, there is Spain (actually in the UTC0 time zone), which orients to its neighbours and accepts other time zones for political and economic reasons rather than using the position of the sun.

This cannot be achieved in large countries, either. In Brazil, for example, there are three different time zones within the country, while there are six in the USA and Russia has eleven. Australia has five time zones, which, depending on the part of the country, are not even separated hourly and do not all have a daylight saving time.

The big outlier is China. Although the country extends over five theoretical time zones, for political reasons, the time zone for Beijing, the capital, has been decreed for the whole country. Thus there is a large time difference at China’s western border to Pakistan and Tajikistan: On the other side of the border, one must change the time a full three hours. For the sake of completeness: Only the autonomous region Xinjiang in the extreme west of China has its own time zone.

The Date Line

The date line runs at the 180th longitude and thus in the middle of the Pacific Ocean. If one crosses this border from west to east, one has to deduct a whole day. From east to west (thus in direction to Asia), one adds one day. This position is not by coincidence. Since a date change has to take place at some point during the 24-hour division, the most remote and sparsely populated place on earth, which lies between America and Asia, was used intentionally for this purpose. From this the position, we get the exact other side of the globe and draw a vertical line, the zero meridian in Greenwich — a suburb of London. Until 1884, completely different coordinate systems were used depending on the country, which also had a date line, but originated in their own country.

Occasionally, individual countries switch from one side of the dateline to the other for political reasons. For example, in 1995, Kiribati placed its former two-day territory in the UTC+12 time zone. Samoa also moved back to the West in 2011 because trade relations with the eastern regions played an increasingly minor role.

Sources

The time zones and times listed here are based on the IANA "Olsen" time zone database. Designations and their translations were adapted beyond that. Version used and update: Version 2024.1 on 04/24/2024.