What do they mean when they say time zone?

Answer 1

A time zone is a geographical area throughout which the time is the same.

Before time zones were introduced in the mid-19th century, every city set its clocks according to when the sun was at its highest elevation in the sky as seen from that location, calling that noon. That time changes by four minutes for every degree of longitude. When transportation and communication started to become faster, it became too confusing for every city to have a different time.

The time in each time zone is specified by its offset, or how far behind or ahead it is, from Coordinated Universal Time (UTC). Each time zone's offset and its borders are specified by the government that has jurisdiction over the area, so time zone borders usually follow geopolitical borders. In many places, one hour is added to the time offset from spring until fall in an effort to conserve energy known as Daylight Saving Time or Summer Time. There are 41 different time offsets used around the world each year. 38 of them are in use from 22nd March to 22nd September, and 39 of them are in use during the other half of each year. One time offset can have several different names, especially in Asia and South America, where time zone names are not shared between countries.

Here are the 41 time zone offsets with the time zone names associated with each one. Places that use Daylight Saving Time/ Summer Time are shown separately from places that do not:

UTC - 11 hours

• Niue Time (NUT) - Niue, New Zealand
• Samoa Standard Time (SST) - US territories of American Samoa & Midway

UTC - 10 hours

• Cook Islands Time (CKT) - Cook Islands
• Hawaii-Aleutian Standard Time (HAST) - Hawaii, USA
• Tahiti Time (TAHT) - the Austral Islands, Society Islands & Tuamotus of French Polynesia

UTC - 10 hours / UTC - 9 hours

• Hawaii-Aleutian Standard Time/ Hawaii-Aleutian Daylight Saving Time (HAST/HADT) - part of the Aleutian Islands of Alaska, USA

UTC - 9.5 hours

• Marquesas Time (MART) - the Marquesas Islands of French Polynesia

UTC - 9 hours

• Gambier Time (GAMT) - the Gambier Islands of French Polynesia

UTC - 9 hours / UTC - 8 hours

• Alaska Standard Time/ Alaska Daylight Saving Time (AKST/AKDT) - most of Alaska, USA

UTC - 8 hours

• Metlakatla Time (MeST) - Annette Island, Alaska, USA
• Pitcairn Standard Time (PST) - the Pitcairn Islands, U.K.

UTC - 8 hours / UTC - 7 hours

• Pacific Standard Time / Pacific Daylight Saving Time (PST/PDT) - parts of Canada, Mexico & the United States

UTC - 7 hours

• Mountain Standard Time (MST) - Sonora, Mexico, most of Arizona, USA, & parts of British Columbia, Canada

UTC - 7 hours / UTC - 6 hours

• Mountain Standard Time/ Mountain Daylight Saving Time (MST/MDT) - parts of Canada, Mexico & the United States

UTC - 6 hours

• Central Standard Time (CST) - Belize, Costa Rica, El Salvador, Guatemala, Honduras & Nicaragua & most of Saskatchewan, Canada
• Galapagos Time (GALT) - the Galapagos Islands of Ecuador

UTC - 6 hours / UTC - 5 hours

• Central Standard Time/ Central Daylight Saving Time (CST/CDT) - parts of Canada & the United States; most of Mexico
• Easter Island Time/ Easter Island Summer Time (EAST/EASST) - Easter Island (Chile)

UTC - 5 hours

• Acre Time (ACT) - parts of Brazil
• Colombia Time (COT) - Colombia
• Eastern Standard Time (EST) - Cayman Islands (UK), Jamaica, Panama, parts of Canada
• Ecuador Time (ECT) - Ecuador
• Peru Time (PET) - Peru

UTC - 5 hours / UTC - 4 hours

• Cuba Standard Time/ Cuba Daylight Saving Time (CUST/CUDT) - Cuba
• Eastern Standard Time/ Eastern Daylight Saving Time (EST/EDT) - Bahamas, Haiti, Turks & Caicos (UK), parts of Canada & the United States

UTC - 4.5 hours

• Venezuelan Standard Time (VET) - Venezuela

UTC - 4 hours

• Amazon Time (AMT) - part of Brazil
• Atlantic Standard Time (AST) - Anguilla (UK), Antigua & Barbuda, Barbados, British Virgin Islands, Dominica, Dominican Republic, Grenada, Guadeloupe (France), Martinica (France), Montserrat (UK), Netherlands Antilles, Puerto Rico (USA), St. Kitts & Nevis, St. Lucia, St. Vincent & Grenadines, Trinidad & Tobago, US Virgin Islands, part of Quebec, Canada
• Bolivia Time (BOT) - Bolivia
• Guyana Time (GYT) - Guyana

UTC - 4 hours / UTC - 3 hours

• Amazon Time/ Amazon Summer Time (AMT/AMST) - part of Brazil
• Atlantic Standard Time/ Atlantic Daylight Saving Time (AST/ADT) - Bermuda (UK) & parts of Canada & Greenland (Denmark)
• Chile Time/ Chile Summer Time (CLT/CLST) - Chile & Palmer, Anvers Island, Antarctica
• Paraguay Time/ Paraguay Summer Time (PYT/PYST) - Paraguay

UTC - 3.5 hours / UTC - 2.5 hours

• Newfoundland Standard Time/ Newfoundland Daylight Saving Time (NST/NDT) - part of Newfoundland & Labrador, Canada

UTC - 3 hours

• Argentina Time (ART) - Argentina
• Brasilia Time (BRT) - part of Brazil
• Falkland Islands Summer Time (FKST) - Falkland Islands (UK)
• French Guiana Time (GFT) - French Guiana
• Rothera Time (ROTT) - Rothera, Adelaide Island, Antarctica
• Suriname Time (SRT) - Suriname

UTC - 3 hours / UTC - 2 hours

• Brasilia Time/ Brasilia Summer Time (BRT/BRST) - part of Brazil
• Pierre & Miquelon Standard Time/ Pierre & Miquelon Daylight Saving Time (PMST/PMDT) - St.-Pierre & Miquelon Islands (France)
• Uruguay Time/ Uruguay Summer Time (UYT/UYST) - Uruguay
• Western Greenland Time/ Western Greenland Summer Time (WGT/WGST) - most of Greenland (Denmark)

UTC - 2 hours

• Fernando de Noronha Time (FNT) - Fernando de Noronha Archipelago of Pernambuco, Brazil
• South Georgia Time (GST) - South Georgia Island & the South Sandwich Islands of the UK

UTC - 1 hour

• Cape Verde Time (CVT) - Cape Verde Islands

UTC - 1 hour / UTC

• Azores Time/ Azores Summer Time (AZOT/AZOST) - Azores Islands of Portugal
• Eastern Greenland Time/ Eastern Greenland Summer Time (EGT/EGST) - part of Greenland (Denmark)

UTC

• Greenwich Mean Time (GMT) - Burkina Faso, Côte d'Ivoire, The Gambia, Ghana, Guinea, Guinea-Bissau, Iceland, Liberia, Mali, Mauritania, Saint Helena, Ascension and Tristan da Cunha Islands (UK), São Tomé and Príncipe, Senegal, Sierra Leone & Togo & part of Greenland (Denmark)

UTC / UTC + 1 hour

• Greenwich Mean Time/ British Summer Time (GMT/BST) - United Kingdom (including England, Scotland, Northern Ireland, Wales, Isle of Mann, Guernsey & Jersey)
• Greenwich Mean Time/ Irish Summer Time (GMT/IEST) - Republic of Ireland
• Western European Time/ Western European Summer Time (WET/WEST) - Canary Islands (Spain), Faroe Islands (Denmark), Morocco, Portugal (incl. the Madeira Islands), Western Sahara

UTC + 1 hour

• Central European Time (CET) - Algeria & Tunisia
• West Africa Time (WAT) - Angola, Benin, Cameroon, Central African Republic, Chad, Congo, Equatorial Guinea, Gabon, Niger & Nigeria & part of D. R. Congo

UTC + 1 hour / UTC + 2 hours

• Central European Time/ Central European Summer Time (CET/CEST) - Albania, Andorra, Austria, Belgium, Bosnia & Herzegovina, Croatia, Czech Republic, Denmark, France, Germany, Gibraltar (UK), Hungary, Italy, Kosovo, Liechtenstein, Luxembourg, Macedonia, Malta, Monaco, Montenegro, Netherlands, Norway (incl. Svalbard), Poland, San Marino, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland & Vatican City
• West Africa Time/ West Africa Summer Time (WAT/WAST) - Namibia

UTC + 2 hours

• Central Africa Time (CAT) - Botswana, Burundi, Malawi, Mozambique, Rwanda, Zambia & Zimbabwe & part of D. R. Congo
• Eastern European Time (EET) - Egypt & Libya
• South Africa Standard Time (SAST) - Lesotho, South Africa & Swaziland

UTC + 2 hours / UTC + 3 hours

• Eastern European Time/ Eastern European Summer Time (EET/EEST) - Akrotiri & Dhekelia (UK), Bulgaria, Cyprus, Estonia, Finland, Greece, Jordan, Latvia, Lebanon, Lithuania, Moldova, Palestinian Territories, Romania, Syria, Transnistria, Turkey & Ukraine
• Israel Standard Time/ Israel Daylight Saving Time (ILST/ILDT) - Israel

UTC + 3 hours

• Arabia Standard Time (AST) - Bahrain, Iraq, Kuwait, Qatar, Saudi Arabia & Yemen
• East Africa Time (EAT) - Comoros, Djibouti, Eritrea, Ethiopia, Kenya, Madagascar, Mayotte (France), Somalia, Somaliland, South Sudan, Sudan, Tanzania & Uganda
• Further-Eastern European Time (FET) - Belarus & Kaliningrad, Russia
• Syowa Time (SYOT) - Syowa Station, Antarctica

UTC + 3.5 hours / UTC + 4.5 hours

• Iran Standard Time/ Iran Daylight Saving Time (IRST/IRDT) - Iran

UTC + 4 hours

• Armenia Time (AMT) - Armenia
• Georgia Time (GET) - Georgia
• Gulf Standard Time (GST) - Oman & United Arab Emirates
• Mauritius Time (MUT) - Mauritius
• Moscow Time (MSK) - part of Russia
• Réunion Time (RET) - Réunion
• Samara Time (SAMT) - part of Russia
• Seychelles Time (SCT) - Seychelles
• Volograd Time (VOLT) - part of Russia

UTC + 4 hours / UTC + 5 hours

• Azerbaijan Time/ Azerbaijan Summer Time (AZT/AZST) - Azerbaijan

UTC + 4.5 hours

• Afghanistan Time (AFT) - Afghanistan

UTC + 5 hours

• Aqtau/Aqtobe Time (AQTT) - part of Kazakhstan
• French Southern & Antarctic Time (TFT) - French Southern & Antarctic Lands
• Maldives Time (MVT) - Maldives
• Mawson Time (MAWT) - Mawson Station, Antarctica
• Oral Time (ORAT) - part of Kazakhstan
• Pakistan Time (PKT) - Pakistan
• Tajikistan Time (TJT) - Tajikistan
• Turkmenistan Time (TMT) - Turkmenistan
• Uzbekistan Time (UZT) - Uzbekistan

UTC + 5.5 hours

• India Standard Time (INST) - India
• Sri Lanka Time (LKT) - Sri Lanka

UTC + 5.75 hours

• Nepal Time (NPT) - Nepal

UTC + 6 hours

• Alma-Ata Time (ALMT) - part of Kazakhstan
• Bangladesh Standard Time (BdST) - Bangladesh
• Bhutan Time (BTT) - Bhutan
• Indian Chagos Time (IOT) - British Indian Ocean Territory
• Kyrgyzstan Time (KGT) - Kyrgyzstan
• Qyzylorda Time (QYZT) - part of Kazakhstan
• Vostok Time (VOST) - Vostok Station, Antarctica
• Yekaterinburg Time (YEKT) - part of Russia

UTC + 6.5 hours

• Cocos Islands Time (CCT) - Cocos (Keeling) Islands of Australia
• Myanmar Time (MMT) - Myanmar

UTC + 7 hours

• Christmas Island Time (CXT) - Christmas Island, Australia
• Davis Time (DAVT) - Davis Station, Antarctica
• Hovd Time (HOVT) - part of Mongolia
• Indochina Time (ICT) - Cambodia, Laos, Thailand & Vietnam
• Novosibirsk/Novokuznetsk Time (NOVT) - part of Russia
• Omsk Time (OMST) - part of Russia
• Western Indonesian Time (WIB) - parts of Indonesia

UTC + 8 hours

• Australian Western Standard Time (AWST) - Western Australia, Australia; Casey Station, Antarctica
• Brunei Darussalam Time (BNT) - Brunei
• Central Indonesian Time (WITA) - parts of Indonesia
• China Standard Time (CNST) - China, Macau & Taiwan
• Choibalsan Time (CHOT) - part of Mongolia
• Hong Kong Time (HKT) - Hong Kong
• Krasnoyarsk Time (KRAT) - part of Russia
• Malaysia Time (MYT) - Malaysia
• Philippine Time (PHT) - The Philippines
• Singapore Time (SGT) - Singapore
• Ulaanbaatar Time (ULAT) - part of Mongolia

UTC + 8.75 hours

• Central Western Standard Time (CWST) - part of WA, Australia

UTC + 9 hours

• Eastern Indonesian Time (WIT) - parts of Indonesia
• Irkutsk Time (IRKT) - part of Russia
• Japan Standard Time (JST) - Japan
• Korea Standard Time (KST) - North Korea & South Korea
• Palau Time (PWT) - Palau
• Timor-Leste Time (TLT) - Timor-Leste

UTC + 9.5 hours

• Australian Central Standard Time (ACST) - Northern Territory, Australia

UTC + 9.5 hours / UTC + 10.5 hours

• Australian Central Standard Time/ Australian Central Daylight Saving Time (ACST/ACDT) - South Australia, Australia

UTC + 10 hours

• Australian Eastern Standard Time (AEST) - Queensland, Australia
• Chamorro Standard Time (ChST) - C.N.M.I. (USA) & Guam (USA)
• Chuuk Time (CHUT) - part of Micronesia
• Dumont-d'Urville Time (DDUT) - Dumont-d'Urville, Ile des Petrels, Antarctica
• Papua New Guinea Time (PGT) - Papua New Guinea
• Yakutsk Time (YAKT) - part of Russia
• Yap Time (YAPT) - part of Micronesia

UTC + 10 hours / UTC + 11 hours

• Australian Eastern Standard Time/ Australian Eastern Daylight Saving Time (AEST/AEDT) - parts of Australia

UTC + 10.5 hours / UTC + 11 hours

• Lord Howe Standard Time/ Lord Howe Daylight Saving Time (LHST/LHDT) - Lord Howe Island, Australia

UTC + 11 hours

• Kosrae Time (KOST) - part of Micronesia
• Macquarie Island Time (MIST) - Macquarie Island, Antarctica
• New Caledonia Time (NCT) - New Caledonia, France
• Pohnpei Time (PONT) - part of Micronesia
• Solomon Islands Time (SBT) - Solomon Islands
• Vanuatu Time (VUT) - Vanuatu
• Vladivostok Time (VLAT) - part of Russia
• Yuzhno-Sakhalinsk Time (SAKT) - part of Russia

UTC + 11.5 hours

• Norfolk Time (NFT) - Norfolk Island, Australia

UTC + 12 hours

• Anadyr Time (ANAT) - part of Russia
• Gilbert Island Time (GILT) - the Gilbert Islands of Kiribati
• Magadan Time (MAGT) - part of Russia
• Marshall Islands Time (MHT) - Marshall Islands
• Nauru Time (NRT) - Nauru
• Petropavlovsk-Kamchatski Time (PETT) - part of Russia
• Tuvalu Time (TVT) - Tuvalu
• Wallis & Futuna Time (WFT) - Wallis & Futuna, France

UTC + 12 hours / UTC + 13 hours

• Fiji Time/ Fiji Summer Time (FJT/FJST) - Fiji
• New Zealand Standard Time/ New Zealand Daylight Saving Time (NZST/NZDT) - New Zealand; McMurdo Station, Ross Island, Antarctica

UTC + 12.75 hours / UTC + 13.75 hours

• Chatham Islands Standard Time/ Chatham Islands Daylight Saving Time (CHAST/CHADT) - Chatham Islands, New Zealand

UTC + 13 hours

• Phoenix Islands Time (PHOT) - the Phoenix Islands of Kiribati
• Tokelau Time (TKT) - Tokelau, New Zealand
• Tonga Time (TOT) - Tonga

UTC + 13 hours / UTC + 14 hours

• Samoa Time/ Samoa Summer Time (WST/WSST) - Samoa

UTC + 14 hours

• Line Islands Time (LINT) - the Line Islands of Kiribati