A time zone is a region on Earth with a uniform standard time for legal, commercial, and social purposes. It is convenient for close commercial or other communication areas to keep the same time, so time zones tend to follow the boundaries of countries and their subdivisions.
Most of the time zones on land are offset from Coordinated Universal Time (UTC) by a whole number of hours (UTC−12 to UTC+14), but a few are offset by 30 or 45 minutes. Some higher latitude countries use daylight saving time for part of the year, typically by changing clocks by an hour. Many land time zones are skewed toward the west of the corresponding nautical time zones. This also creates a permanent daylight-saving time effect.
Alphabetically sorted. Note that some abbreviations are not unique; these will have several entries in the list. Other time zones have many common names, each of which will be listed.
| Abbreviation | Full name | Location | Timezone |
| A | Alpha Time Zone | Military | UTC + 1 hour |
| ACDT | Australian Central Daylight Time | Australia | UTC + 10:30 hours |
| ACST | Australian Central Standard Time | Australia | UTC + 9:30 hours |
| ADT | Atlantic Daylight Time | North America | UTC – 3 hours |
| AEDT | Australian Eastern Dayl. Time or Australian Eastern Summer Time | Australia | UTC + 11 hours |
| AEST | Australian Eastern Standard Time | Australia | UTC + 10 hours |
| AKDT | Alaska Daylight Time | North America | UTC – 8 hours |
| AKST | Alaska Standard Time | North America | UTC – 9 hours |
| AST | Atlantic Standard Time | North America | UTC – 4 hours |
| AWDT | Australian Western Daylight Time | Australia | UTC + 9 hours |
| AWST | Australian Western Standard Time | Australia | UTC + 8 hours |
| B | Bravo Time Zone | Military | UTC + 2 hours |
| BST | British Summer Time | Europe | UTC + 1 hour |
| C | Charlie Time Zone | Military | UTC + 3 hours |
| CDT | Central Daylight Time | Australia | UTC + 10:30 hours |
| CDT | Central Daylight Time | North America | UTC – 5 hours |
| CEDT | Central European Daylight Time | Europe | UTC + 2 hours |
| CEST | Central European Summer Time | Europe | UTC + 2 hours |
| CET | Central European Time | Europe | UTC + 1 hour |
| CST | Central Summer Time | Australia | UTC + 10:30 hours |
| CST | Central Standard Time | Australia | UTC + 9:30 hours |
| CST | Central Standard Time | North America | UTC – 6 hours |
| CXT | Christmas Island Time | Australia | UTC + 7 hours |
| D | Delta Time Zone | Military | UTC + 4 hours |
| E | Echo Time Zone | Military | UTC + 5 hours |
| EDT | Eastern Daylight Time | Australia | UTC + 11 hours |
| EDT | Eastern Daylight Time | North America | UTC – 4 hours |
| EEDT | Eastern European Daylight Time | Europe | UTC + 3 hours |
| EEST | Eastern European Summer Time | Europe | UTC + 3 hours |
| EET | Eastern European Time | Europe | UTC + 2 hours |
| EST | Eastern Summer Time | Australia | UTC + 11 hours |
| EST | Eastern Standard Time | Australia | UTC + 10 hours |
| EST | Eastern Standard Time | North America | UTC – 5 hours |
| F | Foxtrot Time Zone | Military | UTC + 6 hours |
| G | Golf Time Zone | Military | UTC + 7 hours |
| GMT | Greenwich Mean Time | Europe | UTC |
| H | Hotel Time Zone | Military | UTC + 8 hours |
| HAA | Heure Avancée de l’Atlantique | North America | UTC – 3 hours |
| HAC | Heure Avancée du Centre | North America | UTC – 5 hours |
| HADT | Hawaii-Aleutian Daylight Time | North America | UTC – 9 hours |
| HAE | Heure Avancée de l’Est | North America | UTC – 4 hours |
| HAP | Heure Avancée du Pacifique | North America | UTC – 7 hours |
| HAR | Heure Avancée des Rocheuses | North America | UTC – 6 hours |
| HAST | Hawaii-Aleutian Standard Time | North America | UTC – 10 hours |
| HAT | Heure Avancée de Terre-Neuve | North America | UTC – 2:30 hours |
| HAY | Heure Avancée du Yukon | North America | UTC – 8 hours |
| HNA | Heure Normale de l’Atlantique | North America | UTC – 4 hours |
| HNC | Heure Normale du Centre | North America | UTC – 6 hours |
| HNE | Heure Normale de l’Est | North America | UTC – 5 hours |
| HNP | Heure Normale du Pacifique | North America | UTC – 8 hours |
| HNR | Heure Normale des Rocheuses | North America | UTC – 7 hours |
| HNT | Heure Normale de Terre-Neuve | North America | UTC – 3:30 hours |
| HNY | Heure Normale du Yukon | North America | UTC – 9 hours |
| I | India Time Zone | Military | UTC + 9 hours |
| IST | Irish Summer Time | Europe | UTC + 1 hour |
| K | Kilo Time Zone | Military | UTC + 10 hours |
| L | Lima Time Zone | Military | UTC + 11 hours |
| M | Mike Time Zone | Military | UTC + 12 hours |
| MDT | Mountain Daylight Time | North America | UTC – 6 hours |
| MESZ | Mitteleuroäische Sommerzeit | Europe | UTC + 2 hours |
| MEZ | Mitteleuropäische Zeit | Europe | UTC + 1 hour |
| MSD | Moscow Daylight Time | Europe | UTC + 4 hours |
| MSK | Moscow Standard Time | Europe | UTC + 3 hours |
| MST | Mountain Standard Time | North America | UTC – 7 hours |
| N | November Time Zone | Military | UTC – 1 hour |
| NDT | Newfoundland Daylight Time | North America | UTC – 2:30 hours |
| NFT | Norfolk (Island) Time | Australia | UTC + 11:30 hours |
| NST | Newfoundland Standard Time | North America | UTC – 3:30 hours |
| O | Oscar Time Zone | Military | UTC – 2 hours |
| P | Papa Time Zone | Military | UTC – 3 hours |
| PDT | Pacific Daylight Time | North America | UTC – 7 hours |
| PST | Pacific Standard Time | North America | UTC – 8 hours |
| Q | Quebec Time Zone | Military | UTC – 4 hours |
| R | Romeo Time Zone | Military | UTC – 5 hours |
| S | Sierra Time Zone | Military | UTC – 6 hours |
| T | Tango Time Zone | Military | UTC – 7 hours |
| U | Uniform Time Zone | Military | UTC – 8 hours |
| UTC | Coordinated Universal Time | Europe | UTC |
| V | Victor Time Zone | Military | UTC – 9 hours |
| W | Whiskey Time Zone | Military | UTC – 10 hours |
| WDT | Western Daylight Time | Australia | UTC + 9 hours |
| WEDT | Western European Daylight Time | Europe | UTC + 1 hour |
| WEST | Western European Summer Time | Europe | UTC + 1 hour |
| WET | Western European Time | Europe | UTC |
| WST | Western Summer Time | Australia | UTC + 9 hours |
| WST | Western Standard Time | Australia | UTC + 8 hours |
| X | X-ray Time Zone | Military | UTC – 11 hours |
| Y | Yankee Time Zone | Military | UTC – 12 hours |
| Z | Zulu Time Zone | Military | UTC |
The daylight decrease during the winter is due to Earth’s axial tilt of 23 degrees. If the Earth was not tilted on its axis, the length of day and night would remain steady year long. During winter in the northern hemisphere, there are fewer daylight hours, and the southern hemisphere, in turn, has longer daylight hours and experiences summer.
The main purpose of Daylight Saving Time (called “Summer Time” in many places in the world) is to make better use of daylight. In Ireland, we advance our clocks forward by one hour in Spring to maximize daylight for the summer months. This has the effect of moving an hour of daylight from the morning to the evening. In winter, the clocks are changed back by one hour to maximize daylight during the morning hours.
