Time zone
Time zones are areas of the Earth that have adopted the same local time. Formerly, people used apparent solar time, resulting in the time differing slightly from town to town. As telecommunications improved and with the expansion of the railways this became increasingly awkward. Time zones partially rectified the problem by setting the clocks of a region to the same mean solar time. Time zones are generally centered on meridians of a longitude that is a multiple of 15º thus making neighbouring time zones one hour apart. However, the one hour separation is not universal and, as the map below shows, the shapes of time zones can be quite irregular because they usually follow the boundaries of states, countries or other administrative areas.
A map of the world's time zones
All time zones are defined relative to Coordinated Universal Time (UTC). The reference point for Time Zones is the Prime Meridian (longitude 0ÃÂð) which passes through the Royal Greenwich Observatory in Greenwich, London, England [1]. For this reason the term Greenwich Mean Time (GMT) is still often used (by the BBC, for example, amongst others) to denote the "base time" to which all other time zones are relative. UTC is, nevertheless, the official term for today's atomically measured time as distinct from time determined by astronomical observation as formerly carried out at Greenwich.
GMT (UTC) is, incidentally, local time at Greenwich itself only between 01:00 UTC on the last Sunday in October and 01:00 UTC on the last Sunday in March. For the remainder of the year local time is UTC+1 - known in the UK as British Summer Time (BST).
The time for a location is given relative to UTC. Some examples:
- Los Angeles, California, USA: UTC-8 (e.g. if it is 12:00 UTC, then it is 04:00 in Los Angeles)
- New York, New York, USA: UTC-5 (e.g. if it is 11:00 UTC, then it is 06:00 in New York)
- Stockholm, Sweden: UTC+1 (e.g. if it is 12:00 UTC, then it is 13:00 in Stockholm)
- Mumbai, India: UTC+5.5 (e.g. if it is 13:00 UTC, then it is 18:30 in Mumbai)
- Tokyo, Japan: UTC+9 (e.g. if it is 11:00 UTC, then it is 20:00 in Tokyo)
- Cairo, Egypt: UTC+2 (e.g. if it is 23:00 UTC on Monday 15 March, then the time in Cairo is 01:00, Tuesday 16 March)
- Auckland, New Zealand: UTC+12 (e.g. if it is 21:00 UTC on Wednesday 30 June, then the time in Auckland is 09:00, Thursday 1 July)
- New York, USA: UTC-5 (e.g. if it is 02:00 UTC on Tuesday, then the time in NY is 21:00 on Monday)
- Buenos Aires, Argentina: UTC-4 (e.g. if it is 03:00 UTC on Saturday 23 July, then the time in Buenos Aires is 23:00, Friday 22 July)
- Honolulu, Hawai'i, USA: UTC-10 (e.g. if it is 06:00 UTC on Monday 1 May, then the time in Honolulu is 20:00, Sunday 30 April)
- e.g. New Zealand which is usually UTC+12, observes a one-hour daylight saving time adjustment during the southern hemisphere summer resulting in a local time of UTC+13!
The first time zone in the world was established in the 1840s by the Royal Greenwich Observatory for all of England, Scotland, and Wales. Multiple time zones were first proposed by Sandford Fleming because of the need of railroad companies to have consistent local times between railroad stations. [1] On 18 November 1883, railroads in the United States and Canada became the first to institute multiple time zones when they established four standard continental time zones in North America. This ended a great deal of confusion created by previously having thousands of local times. Although a world-wide system of time zones was proposed at the 1884 International Meridian Conference, it did not accept that proposal, declaring that the time used by individual countries was not within the purview of the conference.
See also: Sidereal time Calculating local time
List of time zones and contained areas
Regions with * observe Daylight Saving Time: add 1 hour in summer.
Note that some regions differ 24 hours in time: they have the same time of the day but differ by a full day. The two extreme time zones even differ 25 hours, hence during one hour a day the date differs 2 days.
UTC-12
Military designation: YUTC-11 (BEST - Bering Standard Time)
Military designation: X
UTC-10 (HST - Hawaii-Aleutian Standard Time Zone)
Military designation: W
UTC-9:30
Military designation: V*
UTC-9 (AKST - Alaska Standard Time Zone)
Military designation: V
UTC-8 (PST - Pacific Standard Time Zone)
Military designation: U
UTC-7 (MST - Mountain Standard Time Zone)
Military designation: T
UTC-6 (CST - Central Standard Time Zone)
Military designation: S
UTC-5 (EST - Eastern Standard Time Zone)
Military designation: R
UTC-4 (AST - Atlantic Standard Time)
Military designation: Q
UTC-3:30 (NST - Newfoundland Standard Time)
Military designation: P*
UTC-3
Military designation: P
UTC-2
Military designation: O
UTC-1
Military designation: N
UTC (WET - West European Time)
Military designation: Z
UTC+1 (CET - Central European Time)
Military designation: A
UTC+2 (EET - East European Time)
Military designation: B
UTC+3 (MSK - Moscow Time)
Military designation: C
UTC+3:30
Military designation: C*
UTC+4
Military designation: D
UTC+4:30
Military designation: D*
UTC+5
Military designation: E
UTC+5:30 (IST - Indian Standard Time)
Military designation: E*
UTC+5:45
Military designation: E†
UTC+6
Military designation: F
UTC+6:30
Military designation: F*
UTC+7
Military designation: G
UTC+8 (AWST - Australian Western Standard Time)
Military designation: H
Note that the whole of China has the same time, which makes this time zone exceptionally wide. In the extreme west of China the sun is at its highest at 15:00, in the extreme east at 11:00.UTC+9
Military designation: I
UTC+9:30 (ACST - Australian Central Standard Time)
Military designation: I*
UTC+10 (AEST - Australian Eastern Standard Time)
Military designation: K
The United States has officially designated this time zone Chamorro Standard Time.UTC+10:30
Military designation: K*
UTC+11
Military designation: L
UTC+11:30
Military designation: L*
UTC+12
Military designation: M
UTC+12:45
Military designation: M*
UTC+13
Military designation: M†
UTC+14
Military designation: M‡
See also
External links