The time shown on a clock; technically, it is the time since the mean sun crossed the meridian with 12 hours added to make the day begin at midnight rather than noon. As the variations of apparent solar time due to the equation of time have been averaged out, mean solar time proceeds uniformly except for small irregularities in the gradual slowing of the Earth's rotation. Mean solar time is closely related to mean sidereal time, and one can be calculated if the other is known. The mean solar time on the Greenwich meridian is Universal Time.
Subjects: Astronomy and Astrophysics.