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  2. Universal Time - Wikipedia

    en.wikipedia.org/wiki/Universal_Time

    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 ...

  3. Leap second - Wikipedia

    en.wikipedia.org/wiki/Leap_second

    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 ...

  4. Greenwich Mean Time - Wikipedia

    en.wikipedia.org/wiki/Greenwich_Mean_Time

    [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 ...

  5. Coordinated Universal Time - Wikipedia

    en.wikipedia.org/wiki/Coordinated_Universal_Time

    This is an accepted version of this page This is the latest accepted revision, reviewed on 4 February 2025. 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 ...

  6. DUT1 - Wikipedia

    en.wikipedia.org/wiki/DUT1

    DUT1 is a time correction equal to the difference between Universal Time , which is defined by Earth's rotation, and Coordinated Universal Time (UTC), which is defined by a network of precision atomic clocks, with a precision of +/- 0.1s [1] [2]. DUT1 = UT1UTC (with a precision of +/- 0.1s)

  7. International Earth Rotation and Reference Systems Service

    en.wikipedia.org/wiki/International_Earth...

    UT1 is the non-uniform time defined based on the Earth's rotation. It defined the IERS Reference Meridian, the International Terrestrial Reference System (ITRS), and subsequent International Terrestrial Reference Frames (ITRF). Related coordinate systems are used by satellite navigation systems like GPS and Galileo: WGS84 and GTRF. The ...

  8. Time standard - Wikipedia

    en.wikipedia.org/wiki/Time_standard

    But Coordinated Universal Time (UTC) (an atomic-based time scale which is always kept within 0.9 second of UT1) is in common actual use in the UK, and the name GMT is often used to refer to it. (See articles Greenwich Mean Time , Universal Time , Coordinated Universal Time and the sources they cite.)

  9. List of UTC offsets - Wikipedia

    en.wikipedia.org/wiki/List_of_UTC_offsets

    This is a list of the UTC time offsets, showing the difference in hours and minutes from Coordinated Universal Time (UTC), from the westernmost (−12:00) to the easternmost (+14:00). It includes countries and regions that observe them during standard time or year-round.