What is Leap Second ??? | Addition of Positive and Negative leap sec | UTC Time | Time Zone
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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 (UT1), which varies due to irregularities and a long-term slowdown in the Earth's rotation. The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries, uses TAI and consequently would run ahead of observed solar time unless it is reset to UT1 as needed. The leap second facility exists to provide this adjustment. The leap second was introduced in 1972 and since then 27 leap seconds have been added to UTC.
/ @spacetimereality
A leap second is a second added to Coordinated Universal Time (UTC) to keep it synchronized with astronomical time. UTC is an atomic time scale, based on the performance of atomic clocks that are more stable than the Earth's rotational rate. Astronomical time (UT1), or mean solar time, is based on the rotation of Earth, which is irregular.
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Two main reasons cause leap seconds to occur. The first is that the duration of the atomic second was measured and defined by comparing caesium clocks to the Ephemeris Time (ET) scale, an obsolete time scale that defined the second as a fraction of the tropical year. The duration of the ephemeris second was slightly shorter than the mean solar second and this characteristic was passed along to the atomic second. If the atomic second had been defined concerning the mean solar second, leap seconds would likely have been required much less frequently. The second reason for leap seconds is that the speed of the Earth's rotation is not constant. It sometimes speeds up, and sometimes slows down, but when averaged over long intervals the trend indicates that it is gradually slowing. This gradual decrease in the rotational rate is causing the duration of the mean solar second to gradually increase concerning the atomic second.
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