Time zones are areas of the
Earth that follow the same definition of
time. Formerly, people were using
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 time zone containing London.
See also: Sidereal time
A map of the world's time zones, Larger image
Countries with * observe
Daylight Saving Time: add 1 in
summer.
- Canada (Alberta*, Northwest Territories*, Nunavut (Mountain)*)
- Mexico (Baja California Sur, Chihuahua, Nayarit, Sinaloa, Sonora, South, Central, and Eastern)
- United States (Arizona, Colorado*, Idaho (southern)*, Montana*, Nebraska (western)*, New Mexico*, North Dakota (western)*, South Dakota (western)*, Utah*, Wyoming*)
- Belize
- Canada (Manitoba*, Nunavut (Southampton Island), Nunavut (Central)*, Ontario (Western)*, Saskatchewan)
- Chile (Easter Island)
- Costa Rica
- Ecuador (Galapagos Islands)
- El Salvador
- Guatemala
- Honduras
- Nicaragua
- Puerto Rico
- United States (Alabama*, Arkansas*, Illinois*, Iowa*, Kansas*, Kentucky (western)*, Louisiana*, Minnesota*, Mississippi*, Missouri*, Nebraska (eastern)*, North Dakota*, Oklahoma*, South Dakota (eastern)*, Tennessee (western)*, Texas*, Wisconsin*)
- Brazil (Acre)
- Canada (Nunavut (Eastern)*, Ontario*, Quebec*)
- Cayman Islands
- Colombia
- Cuba*
- Ecuador
- Haiti
- Jamaica
- Panama
- Peru
- Turks and Caicos Islands*
- United States (Connecticut*, Delaware*, District of Columbia*, Florida*, Georgia*, Indiana, Kentucky (eastern)*, Maine*, Maryland*, Massachusetts*, Michigan*, New Hampshire*, New Jersey*, New York*, North Carolina*, Ohio*, Pennsylvania*, Rhode Island*, South Carolina*, Tennessee (eastern)*, Vermont*, Virginia*, West Virginia*)
- Argentina
- Bahamas*
- Brazil (Alagoas, Amapa, Bahia*, Ceara, Distrito Federal*, Espirto Santo[?]*, Goias*, Maranhao, Minas Gerais*, Para (eastern)[?], Paraiba, Parana[?]*, Pernambuco, Piaui, Rio de Janeiro*, Rio Grande do Norte, Rio Grande do Sul*, Santa Catarina*, Sao Paulo*, Sergipe, Tocantins[?]*)
- French Guiana*
- Greenland
- Saint Pierre and Miquelon*
- Suriname
- Uruguay
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 3 pm, in the extreme east at 11 am.
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