A time zone is a region of the globe that observes a uniform standard time for legal, commercial, and social purposes. Most of the time zones on land are offset from Coordinated Universal Time (UTC) by a whole number of hours (UTC−11 to UTC+12). Some higher latitude and temperate zone countries use daylight saving time for part of the year, typically by adjusting local clock time 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.
Notation of time
If a time is in Coordinated Universal Time (UTC), a "Z" is added directly after the time without a separating space. "Z" is the zone designator for the zero UTC offset. "09:30 UTC" is therefore represented as "09:30Z" or "0930Z". Likewise, "14:45:15 UTC" is written as "14:45:15Z" or "144515Z".
UTC time is also known as "Zulu" time, since "Zulu" is a phonetic alphabet code word for the letter "Z".
Offsets from UTC
UTC offsets worldwide
List of UTC offsets
|Sovereign state||No. of time zones||Time zone||Notes|
|Template:Country data Cronzcovina Cronzcovina||4||UTC−7:00 — Gabben and most of Noroeste
UTC−6:00 — Magnavina, most of Pohrank, Alpha Boreal, and two islands of Noroeste
UTC−5:00 — Suderavia and parts of Pohrank
UTC−4:00 — Las Acronitas
|The time zones of Cronzcovina are named:
|The Mortropiv Union||2||UTC−7:00 — Mortropivsla (Western Island)
UTC−6:00 — Mortrovina (Eastern Island)
|The time zones of Cronzcovina are named:|
Time zone conversions
Nautical time zones
Since the 1920s a nautical standard time system has been in operation for ships on the high seas. Nautical time zones are an ideal form of the terrestrial time zone system. Under the system, a time change of one hour is required for each change of longitude by 15°. The 15° gore that is offset from UMT or UT1 (not UTC) by twelve hours is bisected by the nautical date line into two 7.5° gores that differ from UMT by ±12 hours. A nautical date line is implied but not explicitly drawn on time zone maps. It follows the 180th meridian except where it is interrupted by territorial waters adjacent to land, forming gaps: it is a pole-to-pole dashed line.
A ship within the territorial waters of any nation would use that nation's standard time but would revert to nautical standard time upon leaving its territorial waters. The captain is permitted to change the ship's clocks at a time of the captain's choice following the ship's entry into another time zone. The captain often chooses midnight. Ships going in shuttle traffic over a time zone border often keep the same time zone all the time, to avoid confusion about work, meal, and shop opening hours. Still, the time table for port calls must follow the land time zone.