"समय क्षेत्र" का संशोधनहरू बिचको अन्तर

साकुनै सम्पादन सारांश छैन
सा Translating (- and + र )
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 and 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.
 
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]] and [[telecommunication]]s improved, because clocks differed between places by an amount corresponding to the difference in their geographical longitude, which was usually not a convenient number. This problem could be solved by synchronizing the clocks in all localities, but then in many places the local time would differ markedly from the solar time to which people are accustomed. Time zones are thus a compromise, relaxing the complex geographic dependence while still allowing local time to approximate the mean solar time. There has been a general trend to push the boundaries of time zones further west of their designated meridians in order to create a permanent daylight saving time effect. The increase in worldwide communication has further increased the need for interacting parties to communicate mutually comprehensible time references to one another.
 
== 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 and 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 01:00 UTC on the last Sunday in October and 01:00 UTC on the last Sunday in March. For the rest of the year, local time there is [[UTC+1]], known in the [[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 12:00 UTC when daylight saving time (or summer time, etc.) is not in effect:
"https://ne.wikipedia.org/wiki/समय_क्षेत्र" बाट अनुप्रेषित