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Universal Time (UT or UT1) is a time standard based on Earth's rotation. [1] While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle ...
This is an accepted version of this page This is the latest accepted revision, reviewed on 5 December 2024. Primary time standard "UTC" redirects here. For the time zone between UTC−1 and UTC+1, see UTC+00:00. For other uses, see UTC (disambiguation). It has been suggested that UTC offset be merged into this article. (Discuss) Proposed since December 2024. Current time zones Coordinated ...
The two extreme time zones on Earth (both in the mid Pacific) differ by 26 hours. Standard Time Zones, as of January 2, 2024 In the following list, only the rightmost indent of a group of locations is meant to indicate the area observing the offset; the places above and to the left are meant solely to indicate the area's parent administrative ...
Screenshot of the UTC clock from time.gov during the leap second on 31 December 2016.. A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (International Atomic Time (TAI), as measured by atomic clocks) and imprecise observed solar time (), which varies due to irregularities and long-term ...
[5] [6] Today, Universal Time usually refers to Coordinated Universal Time (UTC) or UT1; [7] English speakers often use GMT as a synonym for UTC. [8] For navigation, it is considered equivalent to UT1 (the modern form of mean solar time at 0° longitude); but this meaning can differ from UTC by up to 0.9 s. The term "GMT" should thus not be ...
Such designations can be ambiguous; for example, "CST" can mean China Standard Time (UTC+08:00), Cuba Standard Time (UTC−05:00), and (North American) Central Standard Time (UTC−06:00), and it is also a widely used variant of ACST (Australian Central Standard Time, UTC+9:30). Such designations predate both ISO 8601 and the internet era; in ...
TT is slightly ahead of UT1 (a refined measure of mean solar time at Greenwich) by an amount known as ΔT = TT − UT1. ΔT was measured at +67.6439 seconds (TT ahead of UT1) at 0 h UTC on 1 January 2015; [16] and by retrospective calculation, ΔT was close to zero about the year 1900.
Standard Time (SDT) and Daylight Saving Time (DST) offsets from UTC in hours and minutes. For zones in which Daylight Saving is not observed, the DST offset shown in this table is a simple duplication of the SDT offset. The UTC offsets are based on the current or upcoming database rules.