Time zone

Time zones are areas of the Earth that follow the same definition of time. Formerly, people used apparent solar time, resulting in the time differing slightly from town to town. 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; however as the map below shows, the shapes of time zones can be quite irregular because of boundaries of countries.

All time zones are defined relative to Coordinated Universal Time (UTC). The reference point for Time Zones is the Prime Meridian (longitude 000) 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, as in the rest of Europe, local time is UTC+1 (known in the UK as British Summer Time).

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 New Dehli)
  • Tokyo, Japan: UTC+9 (e.g. if it is 11:00 UTC, then it is 20:00 in Tokyo)

Where the adjustment for time zones results in a time after midnight, then the date at the location is one day later. Some examples:
  • 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)

Where the adjustment for time zones results in a time before 00:00 (i.e. midnight), then the date at the location is one day earlier. Some examples:
  • 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, Hawaii, 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)

Note: The time zone adjustment for a specific location may vary due to the use of daylight saving time. The military refers to time zones using single letter designations. "Z" is used to denote UTC, time zones ahead of UTC are designated using letters in the first half of the Roman alphabet, and time zones behind UTC are designated using the second half. Time zones with a deviation from UTC of a non-integer quantity of hours use the letter of the nearest whole hour-deviated time zone toward UTC, with a star or dagger added on. The letter "J" refers to local time. There are no jurisdictions that observe the time zone designated by the letter "Y" (UTC-12), but that particular time zone is acknowledged as a point of convenience.

Time zones were invented by Sanford 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 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. Worldwide adoption of time zones followed the next year.

See also: Sidereal time Calculating local time


A map of the world's time zones,

Table of contents
1 List of time zones and contained areas
1.1 UTC-11 (BEST - Bering Standard Time)
1.2 UTC-10 (HST - Hawaii-Aleutian Standard Time)
1.3 UTC-9:30
1.4 UTC-9 (AKST - Alaska Standard Time)
1.5 UTC-8 (PST - Pacific Standard Time)
1.6 UTC-7 (MST - Mountain Standard Time)
1.7 UTC-6 (CST - Central Standard Time)
1.8 UTC-5 (EST - Eastern Standard Time)
1.9 UTC-4 (AST - Atlantic Standard Time)
1.10 UTC-3:30 (NST - Newfoundland Standard Time)
1.11 UTC-3
1.12 UTC-2
1.13 UTC-1
1.14 UTC (WET - West European Time)
1.15 UTC+1 (CET - Central European Time)
1.16 UTC+2 (EET - East European Time)
1.17 UTC+3 (MSK - Moscow Time)
1.18 UTC+3:30
1.19 UTC+4
1.20 UTC+4:30
1.21 UTC+5
1.22 UTC+5:30
1.23 UTC+5:45
1.24 UTC+6
1.25 UTC+6:30
1.26 UTC+7
1.27 UTC+8 (AWST - Australian Western Standard Time)
1.28 UTC+9
1.29 UTC+9:30 (ACST - Australian Central Standard Time)
1.30 UTC+10 (AEST - Australian Eastern Standard Time)
1.31 UTC+10:30
1.32 UTC+11
1.33 UTC+11:30
1.34 UTC+12
1.35 UTC+12:45
1.36 UTC+13
1.37 UTC+14
2 External links

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-11 (BEST - Bering Standard Time)

Military designation: X

UTC-10 (HST - Hawaii-Aleutian Standard Time)

Military designation:
W

UTC-9:30

Military designation:
V*

UTC-9 (AKST - Alaska Standard Time)

Military designation:
V

UTC-8 (PST - Pacific Standard Time)

Military designation:
U

UTC-7 (MST - Mountain Standard Time)

Military designation:
T

UTC-6 (CST - Central Standard Time)

Military designation:
S

UTC-5 (EST - Eastern Standard Time)

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

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*
  • Australia (Lord Howe Island*)(DST only 0:30)

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‡

External links


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