What is a time zone?

A time zone is a region on Earth where the same standard time is used. Within a single country, region or group of countries, the clock therefore shows the same time at any given moment. Time zones make it possible to schedule appointments worldwide, plan travel and know clearly what time it is somewhere else in the world.

In the past, almost every place had its own local time. That time was determined by the position of the sun. When the sun was at its highest point, it was locally around twelve noon. That worked well in an era when people travelled little and mainly lived according to the clock of their own village or town. With the arrival of railways, international trade, radio, telephony and later the internet, a shared system of time became essential.

Why do time zones exist?

The Earth rotates once on its axis in roughly 24 hours. As a result, it becomes light and dark at different times in different places. In theory, you can divide the Earth into 24 time zones of one hour each. Because a full circle is 360 degrees, one time zone corresponds to approximately 15 degrees of longitude.

In practice, time zones do not run in neat straight lines across the world map. Countries often choose a time zone that fits best politically, economically or practically. That is why time zones usually follow national borders and sometimes regional borders as well. Some countries use one time zone, while others use several.

UTC: the basis of world time

Most time zones are expressed as an offset from UTC. UTC stands for Coordinated Universal Time and forms the international basis for time indications. A time zone is written, for example, as UTC+1, UTC+2 or UTC-5.

The Netherlands and Belgium use Central European Time, or UTC+1, in winter. During daylight saving time, the clock moves forward one hour and the Netherlands and Belgium use UTC+2.

UTC is very similar to GMT, Greenwich Mean Time. GMT is historically linked to the prime meridian at Greenwich in London. In everyday use, UTC and GMT are sometimes used interchangeably, but technically UTC is the international standard today.

How does time difference between countries work?

The time difference between countries is determined by their time zone. If it is 12:00 in the Netherlands during standard time, for example, it is 11:00 in London, because the United Kingdom then uses UTC+0 and the Netherlands UTC+1.

If you travel further east, it usually becomes later. If you travel west, it usually becomes earlier. There are exceptions, however. Some countries choose a time zone that does not exactly match their geographic location. There are also countries with time zones that differ not by a full hour, but by half an hour or even a quarter of an hour.

Examples include Afghanistan with UTC+4:30 and Nepal with UTC+5:45. As a result, the time difference between countries can sometimes seem less logical than you would expect from a world map.

Why don't time zones always run straight?

On a map, time zones sometimes look irregular and uneven. That is because in practice they are determined not only by the position of the sun, but also by human choices. Borders, economics, trade, transport and political agreements all play a role.

A country may decide to use the same time zone as an important neighbour, so that trade, transport and communication become simpler. A large country may also choose to use one time zone for national unity, even if the sun rises at very different times in the west and east of that country.

A well-known example is China. Although China could geographically have several time zones, the entire country officially uses one time zone: UTC+8. As a result, clock time in western China can differ greatly from local solar time.

Countries with multiple time zones

Some countries are so large or have so many overseas territories that they use multiple time zones. Russia, for example, has a large number of consecutive time zones because the country stretches far from west to east.

France also has many time zones when overseas territories are included. Think of areas in the Caribbean, the Pacific Ocean and other parts of the world. Internationally, France therefore has a remarkably large number of time zones when its overseas territories are counted.

The International Date Line

In addition to time zones, the International Date Line also plays an important role. This imaginary line runs roughly through the Pacific Ocean. When you cross this boundary, you move forward or back one calendar day.

Because of the shape of the date line and the different time zones, the same calendar date can occur somewhere on Earth for a very long time worldwide. While a new day has already begun on some islands in the Pacific, it is still the previous day in other places.

One of the earliest places where a new calendar day begins is Kiribati. There, local time can be as much as 14 hours ahead of UTC. On the other side of the world, there are areas that lag as much as 12 hours behind UTC. As a result, several calendar dates can be in use on Earth at the same moment.

The history of time zones

Before the introduction of time zones, almost every place used its own local time. That local time was based on the sun. When the sun was at its highest point, it was considered twelve o'clock. In an era without fast means of transport, that was not a major problem. People lived locally and rarely travelled long distances.

That changed in the nineteenth century. With the rise of railways, it became increasingly important for cities and stations to use the same time. Trains had to run according to timetables and travellers had to be able to rely on departure and arrival times. If every city used a different local time, that led to confusion.

The arrival of the telegraph, radio and later international communication also made uniform time increasingly important. Time zones therefore arose mainly out of practical necessity: the world became faster, more mobile and better connected.

Time zones in the Netherlands

In the Netherlands, the introduction of a national time was not arranged all at once. For a long time, places used their own local time. In the nineteenth century, railway companies decided to use one fixed railway time at stations. That was based on the time of Amsterdam.

As a result, the clock at the station could show a different time than the tower clock in the same place. That was confusing for travellers, but it showed why a uniform time became increasingly necessary.

In 1909 it was legally established that the whole of the Netherlands would use the same time. Later, Dutch time was simplified further. During the Second World War, Central European Time was introduced in the Netherlands. Since then, the Netherlands has been one hour ahead of UTC in winter.

Time zones in Belgium

Belgium also had local times in the past, but at the end of the nineteenth century it adopted Greenwich time. A national standard time was thus used. During the German occupation in the Second World War, Central European Time was also introduced in Belgium.

Like the Netherlands, Belgium now uses UTC+1 in winter and UTC+2 in summer. As a result, the Netherlands and Belgium almost always have the same clock time.

Daylight saving time and standard time

In addition to standard time, many countries also have daylight saving time. During daylight saving time, the clock is set forward one hour. The original aim was to make better use of daylight and save energy.

The Netherlands and Belgium both use daylight saving time today. In spring the clock moves forward one hour and in autumn it moves back one hour. As a result, the Netherlands and Belgium use UTC+1 in winter and UTC+2 in summer.

Not all countries use daylight saving time. Some countries have abolished it, while others have never used it. As a result, the time difference between countries can change during the year.

Why is knowledge of time zones useful?

Time zones are important for anyone in contact with people in other countries. Think of international phone calls, online meetings, flights, holidays, live events, sports matches and financial markets.

Time zones are also indispensable for websites, apps and computer systems. A calendar appointment, departure time or live stream must be displayed in the correct local time. Without clear time zones, international planning would be much more complicated.

Anyone who wants to know what time it is somewhere in the world therefore looks not only at the country or city, but also at the time zone used and any daylight saving time.

Summary

A time zone is a region where the same standard time applies. Time zones arose because local solar time was no longer practical in a world of railways, international trade, fast communication and global travel. The international standard time UTC forms the basis for most time zones.

Although the Earth can theoretically be divided into 24 one-hour time zones, reality is much more complex. National borders, political choices, daylight saving time and time zones that differ by half or quarter hours mean that world time does not always follow a straight line.

Yet time zones make it possible to communicate clearly about time worldwide. Whether you are planning a trip, have an online meeting or simply want to know what time it is in another city: time zones provide structure in global time.