"समय क्षेत्र" का संशोधनहरू बिचको अन्तर
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पङ्क्ति ३:
[[Image:Timezones optimized.png|thumb|400px|Standard Time Zones of the World as of 2005. (Some time zones have changed since then)]]
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
There are variations of the definitions of ''time zone'' which generally fall into two meanings: a time zone can represent a region where the local time is some fixed offset from a global reference (usually UTC), or a time zone can represent a region throughout which the local time is always consistent even though the offset may fluctuate seasonally.
पङ्क्ति ९:
Before the adoption of time zones, people used local [[solar time]] (originally ''apparent'' solar time, as with a [[sundial]]; and, later, ''mean'' solar time). Mean solar time is the average over a year of apparent solar time. Its difference from apparent solar time is the [[equation of time]].
This became increasingly awkward as [[rail transport|railways]]
== Standard time zones ==
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
Due to [[daylight saving time]], UTC is local time at the [[Royal Observatory, Greenwich]] only between 01:00 UTC on the last Sunday in October
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 12:00 UTC when daylight saving time (or summer time, etc.) is not in effect:
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