"समय क्षेत्र" का संशोधनहरू बिचको अन्तर

Standard time zones can be defined by geometrically subdividing the Earth's [[spheroid]] into 24 [[lune]]s (wedge-shaped sections), bordered by [[meridians]] each 15° of [[longitude]] apart. The local time in neighbouring zones would differ by one hour. However, political र geographical practicalities can result in irregularly-shaped zones that follow political boundaries or that change their time seasonally (as with [[daylight saving time]]), as well as being subject to occasional redefinition as political conditions change.

Earlier, time zones based their time on Greenwich Mean Time (GMT, also called [[UT1]]), the mean solar time at longitude 0° (the [[Prime Meridian]]). But as a mean solar time, GMT is defined by the rotation of the Earth, which is not constant in rate. So, the rate of [[atomic clock]]s was annually changed or steered to closely match GMT. But on [[January 1]], [[1972]] it became fixed, using predefined [[leap second]]s instead of rate changes. This new time system is [[Coordinated Universal Time]] (UTC). Leap seconds are inserted to keep UTC within 0.9 seconds of UT1. In this way, local times continue to correspond approximately to mean solar time, while the effects of variations in Earth's rotation rate are confined to simple step changes that can be easily subtracted if a uniform [[time scale]] ([[International Atomic Time]] or TAI) is desired. With the implementation of UTC, nations began to use it in the definition of their time zones instead of GMT. As of 2005, most but not all nations have altered the definition of local time in this way (though many media outlets fail to make a distinction between GMT र UTC). Further change to the basis of time zones may occur if proposals to abandon leap seconds succeed.