"समय क्षेत्र" का संशोधनहरू बिचको अन्तर

Standard time zones can be defined by geometrically subdividing the Earth's [[spheroid]] into 24२४ [[lune]]s (wedge-shaped sections), bordered by [[meridians]] each 15१५° 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 0०° (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 0०.9९ seconds of UT1UT१. 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 2005२००५, 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.

Due to [[daylight saving time]], UTC is local time at the [[Royal Observatory, Greenwich]] only between 01०१:00०० UTC on the last Sunday in October र 01०१:00०० UTC on the last Sunday in March. For the rest of the year, local time there is [[UTC+1]], known in the [[संयुक्त अधिराज्य|United Kingdom]] as [[British Summer Time]] (BST). Similar circumstances apply in many places.

The definition for time zones can be written in short form as UTC±''n'' (or GMT±''n''), where ''n'' is the offset in hours. These examples give the local time at various locations at 12१२:00०० UTC when daylight saving time (or summer time, etc.) is not in effect:

* [[San Francisco, California|San Francisco]], [[California]], [[संयुक्त राज्य अमेरिका|United States]]: [[UTC-8]]; 04०४:00००

* [[Saint John, New Brunswick]], [[Canada]]: [[UTC-4]]; 08०८:00००

* [[Toronto, Ontario|Toronto]], [[Ontario]], [[Canada]]: [[UTC-5]]; 07०७:00००

* [[Stockholm]], [[Sweden]]: [[UTC+1]]; 13१३:00००

* [[Cape Town]], [[South Africa]]: [[UTC+2]]; 14१४:00००

* [[Mumbai]], [[भारत|India]]: [[UTC+5:30]]; 17१७:30३०

* [[Seoul]], [[कोरिया|Korea]]: [[UTC+9]]; 21२१:00००

* [[Melbourne]], [[अष्ट्रेलिया|Australia]]: [[UTC+10]]; 22२२:00००

Where the adjustment for time zones results in a time at the other side of midnight from UTC, then the date at the location is one day later or earlier. Some examples when UTC is 23२३:00०० on Monday when daylight saving time is not in effect:

* [[Cairo]], [[मिश्र|Egypt]]: UTC+2२; 01०१:00०० on Tuesday

* [[Wellington]], [[New Zealand]]: [[UTC+12]]; 11११:00०० on Tuesday

Some examples when UTC is 02०२:00०० on Tuesday when daylight saving time is not in effect:

* [[New York City]], [[New York]], United States: [[UTC-5]]; 21२१:00०० on Monday

* [[Honolulu]], [[Hawaii]], United States: [[UTC-10]]; 16१६:00०० on Monday