World Time Zones

Time zones

When it is noon in Rio de Janeiro, it is midnight in Tokyo. The reason for this is that we divide the Earth into different time zones. Within each zone, people set their clock for the same time. If someone is traveling by plane between two zones, he or she will adjust his/her clock to the one used in the new zone.

Division of time

There are 24 different timezones, separated by one-hour intervals with each 15 degrees longitude. The zones measured according to the Greenwich Mean Time used as the starting meridian, that measured in hours before and after GMT.

Governments can change their country’s time zone. Thus, for convenience, entire countries tend to adjust to the same local time rather than adjusting exactly to the zones. For example, China could be divided into several time zones, but instead, the whole country uses the same time. Some areas, such as parts of India, Iran, and Australia, use non-standard half-hour deviations.

Summertime

Some countries change their clock in the summer. In Britain, for example, everyone sets their clocks one hour ahead. This is called daylight saving time – one way to give people an extra day of sunshine in the evening. With summertime, countries reduce energy consumption because people use less electricity for lighting.

Changing dates

On the opposite side of the Earth to the starting meridian, there is a date-line that runs mainly through the Pacific Ocean, avoiding the mainland. The locations to the west are 24 hours ahead of the east of the line. This means that if we travel through it in the east, we will lose one day, while we will gain one day to the west.

The map below shows the different time zones of the world. Move your cursor above the country you want to see current time for and click to view time zone and your actual time details.

Scroll with your mouse to zoom, or use zoom buttons on the left side of the map. For Google Street View pull that small yellow man from the left side on the map.

One day around the earth

The development of transport and communication at the end of the 1820s necessitated the introduction of a uniform time reference for the whole earth: 24 time zones were designated.

Greenwich Mean Time (GMT) was created in 1675 to allow sailors to determine their position across the globe accurately. At the end of the 19th century, the Earth was divided into 24 time zones, each of 15 degrees longitude, and on the opposite side of Greenwich South Circle, an international date-line designated.

For practical reasons, the boundaries of the zones have adapted to geographical and political boundaries, many of which have involved changes in time zones. In countries that use the summer-winter time to save energy, local time varies by + 1 hour in summer. The time shift is resulting from the unevenness of the earth’s rotation. Corrected based on the world time measured by the atomic clock since 1972: The difference between the new Universal Central Time (UTC) and Greenwich Mean Time is 0.9 seconds.

Time zones of the World