The new definition of universal time
Abstract
Universal time, UT1, is formally defined by an expression which relates it to mean sidereal time, the latter quantity being directly obtained from the apparent right ascensions of transiting stars. The current formula which relates universal and sidereal time is based on Newcomb's (1895) expression for the right ascension of the fictitious mean sun. The planned introduction on January 1, 1984, of improvements to the definition of the astronomical reference system and the equinox of FK5 necessitate a reexamination of the definition of UT1. The problem of the redefinition of universal time is considered, and a new expression relating universal time and sidereal time is developed for use with the new astronomical reference system. The new expression is based on the final values adopted for the position of the FK5 equinox, and is given to the same precision as that of the new precession expressions.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 January 1982
 Bibcode:
 1982A&A...105..359A
 Keywords:

 Sidereal Time;
 Universal Time;
 Astrometry;
 Celestial Reference Systems;
 Astrophysics