|1.||UT (from 1928) name adopted internationally for Greenwich Mean Time (measured from Greenwich midnight), now split into several slightly different scales, one of which (UT1) is used by astronomers|
|2.||Also called: universal coordinated time, UTC An internationally agreed system for civil timekeeping introduced in 1960 and redefined in 1972 as an atomic timescale. Available from broadcast signals, it has a second equal to the International Atomic Time (TAI) second, the difference between UTC and TAI being an integral number of seconds with leap seconds inserted when necessary to keep it within 0.9 seconds of UT1|
The mean time for the meridian at Greenwich, England (0° longitude), which runs through the former site of the Royal Observatory. It is based on the sidereal period of Earth's rotation and is used as a basis for calculating standard clock time throughout most of the world. Also called Greenwich Mean Time. Compare coordinated universal time.
The measure of time obtained from the rotation of the Earth, also known as Greenwich mean time, after the Greenwich Observatory in England. The world's time standard today is Coordinated Universal Time, which is kept by atomic clocks. The two universal times are kept in synchronization by the occasional insertion of leap seconds into the year.