A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time. It is used to accommodate the difference between precise time and imprecise observed solar time. It has been used since the 1970s and is now being debated by the relevant standards body, the International Committee for Weights and Measures (ICW)
About Leap second in brief
A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time. It is used to accommodate the difference between precise time and imprecise observed solar time. Because the Earth’s rotation speed varies in response to climatic and geological events, UTC leap seconds are irregularly spaced and unpredictable. This practice has proven disruptive, particularly in the twenty-first century and especially in services that depend on precise time stamping or time-critical process control. The relevant international standards body has been debating whether or not to continue the practice. The rate of UTC atomic clocks was slowed by the BIH to remain synchronized with UT2, a practice known as the “rubber second’’. In 1966, the CCIR approved a rate of 0.2s to keep UT2 within 0.1s of UT2 because it had no other way to keep it within 1 s ofUT2. This predominately shifted frequency of 1s to 1s when a broadcast by MSF, WWV, CHU and CHU among other time stations was broadcast by the time of the leap second. The change was approved in 1966, and the rate of atomic time was adjusted by 0.150 parts per 1010 for 1960–1962, by −150 partsper 1010 again for 1964–1971, and by 1.300 parts per1010 for 1966–1971. It was decided at the start of each year, and was slower than the rate of time change in the 1960s and 1970s.
The leap second facility exists to provide this adjustment. It is usually decided about six months in advance by the International Earth Rotation and Reference Systems Service to ensure that the difference. between the UTC and UT1 readings will never exceed 0. 9 seconds. It has been used since the 1970s and is now being debated by the relevant standards body, the International Committee for Weights and Measures (ICW). It is also used by the U.S. Air Force and the Department of Energy. The International Astronomical Union (IAU) uses the second as a fraction of the sidereal year. The second was proposed in 1874 as the base unit of time in the CGS system of units. In 1955, considering the tropical year to be more fundamental, the IAU redefined it as the fraction 1⁄31,556,925. 975 of the 1900. 0 mean tropical year. In 1967, the SI second was again redefined as 9,192,631,770 periods of the radiation emitted by a caesium-133 atom in the transition between the two hyperfine levels of its ground state. The SI second agreed to 1 part in 1010 with the astronomical second then in use. In 1956, a slightly more precise value of 9747 was adopted for the definition of the second by the ICW. In 1960, it was felt necessary to maintain agreement with the GMT time of day, which was the reference for broadcast time services.