The 24 regions of the earth's surface according to the division of the meridian. When we see the sun rising in Shanghai, the people who live in Singapore will have to see the sun rise more than half an hour. And the inhabitants of London in the UK are still sleeping, it is 8 hours to see the sun. People around the world, in the life and work if they use local time, for everyday life, transportation, will bring many difficulties and difficulties. In order to take care of the use of the region, but also to other places of the local time to convert to other local time. Relevant international conference on the surface of the earth along longitude from east to west, formatted with one area, and provides region adjacent to the difference in time between 1 hour. In the same area of the East and the west to see the sun rises most time is only 1 hours. When people cross a region, the clock is corrected for 1 hours (1 hours West to 1 hours), plus or minus a few hours across several regions. So it is convenient to use. Today, the world is divided into 24 time zones. Due to the practical often a country [3], or a province and astride two or more zones, in order to take care of to the administrative convenience, to draw together a nation or a province. So the time zone is not strictly divided by the north and south line, but by the natural conditions. For example, China has a vast territory, almost across 5 time zones, but in fact in the East eight time zone of the standard that the Beijing time.

Area: a global unified time system according to the measurement of time. When the sun is at twelve o'clock. But in different places to see the sun of the time is not the same. For example, Shanghai is already 12 o'clock at noon, the inhabitants of Moscow even after 5 hours to see sun overhead; and Sydney, Australia already is at 2 o'clock in the afternoon. So if you use the local time standard, will give the administrative management, transportation, and daily life, bring a lot of inconvenience. In order to overcome this difficulty, astronomers have to discuss a solution to the problem: will the world longitude 15 degrees across the region, so that a total of 24 regions. In each region the unified time standard, known as the "zone". The area adjacent area is a difference of 1 hours. When people from one area to the east of the region to the adjacent area, the clock will be set aside 1 hours. On the contrary, when people from one area to the adjacent area to the west, the clock will slow down to 1 hours. Waiting at the airport transportation center. Often corresponding to each big city in the world area, using map out, to facilitate the passengers.

Chinese time zone (the period of Republic of China)

China is divided into five zones: 1 time zones: Central Plains, to 120 degrees east longitude central meridian. 2, Gansu and Sichuan: time zone to 105 degrees east longitude central meridian. 3, Tibet: time zone to 90 degrees east longitude central meridian. 4, KunLun: time zone to the east longitude 75 (82.5) of the central meridian. 5, Changbai time zone: to the east longitude 135 (127.5) of the central meridian. After 1949, use the Beijing time.