The sequence of events is:Ģ3h 59m 59s - 23h 59m 60s - 00h 00m 00s Leap Seconds Inserted into the UTC Time Scale Date The table below lists all leap seconds that have already occurred, or are scheduled to occur.Īll leap seconds listed in the table are positive leap seconds, which means an extra second is inserted into the UTC time scale. Leap seconds are used to keep the difference between UT1 and UTC to within ☐.9 s. The first leap second was inserted into the UTC time scale on June 30, 1972. The current difference between UTC and TAI is 37 seconds. This correction keeps UTC in conjunction with the apparent position of the Sun and the stars, and it is the standard used for all general timekeeping applications. Leap SecondsĬoordinated Universal Time (UTC) is based on International Atomic Time (TAI), but it is adjusted by leap seconds to account for the difference between the definition of the second and the rotation of Earth. See information about why we need leap seconds. Its purpose is to keep the UTC time scale within ☐.9 s of the UT1 astronomical time scale, which changes slightly due to variations in the rotation of the Earth. Occasionally, 1 s is added to the UTC time scale. The master clock pulses used by the WWV, WWVH, WWVB, ACTS and Internet Time Service (ITS) time code transmissions are referenced to the UTC(NIST) time scale. This page is updated monthly and contains a table of leap seconds, the current difference between the UT1 and UTC time scales, and the current UT1 - UTC difference that is being broadcast by NIST (called the DUT1 correction).
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