Time zones

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World time zones. Click for larger view.

This is a list of countries, regions, and territories grouped by time zone.

Although many time zones have descriptive names used by people in them, they are least ambiguously identified by their relationship to UTC (Universal Time, Co-ordinated). UTC used to be called GMT (Greenwich Mean Time), after the Royal Observatory located in the Greenwich area of London.

UTC is also sometimes called Z or Zulu time. A time may be written as e.g. 21:45Z with the Z indicating UTC. The "Z" is for "zero", and "Zulu" is the two-way radio pronunciation of "Z". It comes from the nautical system in which each time zone was assigned a letter.

Time zones east of UTC and west of the International Date Line are specified by the number of hours ahead of UTC (e.g. UTC+4); zones west of UTC and east of the Date Line are specified by the number of hours behind UTC (e.g. UTC-6). Crossing the Date Line going eastward, clocks are turned back a full 24 hours, and vice versa in the opposite direction. (Note: The total span of time zones covers more than 24 hours because the Date Line jogs westward and eastward to keep certain national island groupings on the same calendar day, although they are not within a single time zone.)

Travel across time zones[edit]

You need to take some care when planning trips that span time zones, e.g.,:

  • Your "body clock" may experience some stress as you "tell" it to meet business appointments, tours and other obligations perhaps a few or several hours different from the hours you normally rest.
  • You may miss important obligations simply by not understanding what will be the correct local time as you travel.
  • Crossing the International Date Line can cause confusion about on what date you'll arrive, e.g.,:
    • Starting a 12–15 hour flight from the U.S. west coast to Japan or Hong Kong in late evening can land you there in the morning two calendar days later.
    • If starting the reverse course by midday, you may in a way "travel back in time" as you land earlier than you started. For example a typical flight from Sydney to LA will take off at lunchtime and land early in the morning on the same calendar date!

If your travel has time zone complexities or possible impacts on your health or comfort, consult an expert as you plan it.

Jet lag[edit]

See also: Jet lag

Jet lag is a mismatch between your body clock and the local time wherever you are. It's caused by rapid travel across time zones, and compounded by the fact that long hours spent on a plane can cause you to sleep too much, or not enough, possibly at the wrong time. Flights from east to west, where you gain a few hours, are usually a bit easier, as most people find it easier to stay up a little later than to go to bed earlier. A rule of thumb is that you recover about 1 hour difference per day. You may find that on your way out, you are fine after just a couple of days, but you will really notice the recovery period on your way home. At that point your body clock will be really confused and it will take a while for it to sort things out.

You can aid the process a bit by trying to operate on your new local time as early as possible, and spending the daylight hours first few days in your new time zone outdoors. If you're going to land early in the day, try to sleep on the plane so you arrive refreshed and ready for a full day of activity. Conversely, if you're going to arrive near the evening, try to stay awake on the plane so that you'll be tired when you arrive and can get a lengthy sleep.

Daylight Saving Time[edit]

In many jurisdictions, local time is set forward by an extra hour in summer to "shift" daylight hours to the end of the day. This is known in the UK as British Summer Time (BST, GMT+1) and almost anywhere else as Daylight Saving Time (DST) or (name of local time zone) Daylight Time.

In temperate northern countries, DST usually starts late March/early April and ends late October/early November; exact start dates vary by country. Equatorial nations typically use no DST; southern nations will use dates that match their local summer. It's not unheard of for an individual province or state — or even a piece of one province — to opt out of a DST scheme in effect in the rest of the same nation.

List of time zones[edit]




13:48, Stratford, New Zealand





15:15, Sydney Central station





13:53, Tokyo, Japan


23:25, Kuala Lumpur, Malaysia


09:29, Non Sung, Thailand





17:01, Kerala, India




13:52, Volgograd, Russia



10:43, Moshi, Tanzania


21:50, Sighisoara, Romania


13:52, Seligenstadt, Germany
19:57, Tripoli, Libya


12:00, Big Ben, London
15:38, Évora, Portugal




17:24, Buenos Aires, Argentina



16:27, Halifax, Canada



15:20, Independence Hall, Philadelphia, USA


11:38, Mexico City



23:36, San Diego, CA, United States




15:03, Honolulu, HI, United States



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