time, standard (UT) The mean solar time along the prime
meridian (0 longitude) that runs through the Greenwich
Observatory outside of London, UK, where the current system
originated. UT is tied to the rotation of the Earth in
respect to the fictitious "mean Sun".
midday until 1925 when the reference point was changed from
noon to midnight and the name changed to "Universal Time".
There are three separate definitions, UT0, UT1, and UT2,
depending on which corrections have been applied to the
0.9 seconds of UT1, by addition of leap seconds to
(2001-08-02)