Sidereal time Sidereal time is a reading of time based on the positions of the stars rather than the sun. A sidereal day, that is, the time between successive transits of a particular star, is approximately 23 hours, 56 minutes and 4.09 seconds long. For an example of a clock that tells sidereal time, see the Sidereal Tompion Regulator No. 483, by Thomas Tompion and Edward Banger, dated to 1708.
