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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. 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)

  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 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 ...

  6. Wikipedia : Featured picture candidates/Leapsecond.ut1-utc

    en.wikipedia.org/.../Leapsecond.ut1-utc

    Plot showing the difference UT1UTC in seconds. Vertical segments correspond to leap seconds. Red part of graph was prediction (future values) at the time the file was made. Graph showing the difference between UTC (based on an atomic clock with leap seconds) and UT1 (based on the movement of the Earth).

  7. Terrestrial Time - Wikipedia

    en.wikipedia.org/wiki/Terrestrial_Time

    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.

  8. 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 ...

  9. ΔT (timekeeping) - Wikipedia

    en.wikipedia.org/wiki/ΔT_(timekeeping)

    TT-UT1 2000+ ΔT vs. time from 1657 to 2022 [1] [2] In precise timekeeping, ΔT (Delta T, delta-T, deltaT, or DT) is a measure of the cumulative effect of the departure of the Earth's rotation period from the fixed-length day of International Atomic Time (86,400 seconds).