Time Zone

A region of the earth which has a uniform time is called time zone. It is generally referred as the local time of that region. Local time is calculated by UTC plus the current time zone offset for a measured location. This time zone difference is caused by earth’s rotation.

It is divided into standard and daylight saving. Daylight saving time is also known as summer time zone. For daylight saving time offset is includes by summer time zone. For Standard time zones the Earth's spheroid is geometrically subdivided into 24 wedge-shaped sections, surrounded by meridians each 15° of angular distance apart.

The local time in adjacent zones would differ by one hour. Nevertheless, political boundaries, geographical practicalities, and convenience of inhabitants can result in irregularly-shaped zones. Furthermore, in a few regions, half-hour or quarter-hour differences are also in effect.

Before the acceptance of time zones, people used local solar time. In the beginning this was evident or true solar time, as shown by a timekeeper, and later it became mean solar time, which was kept by most mechanical clocks. Mean solar time has days of equal length, but the difference between mean and apparent solar time, called the equation of time, which averages to zero over a year.