solar time

Time of day as determined by the position of the Sun in the sky.

Apparent solar time, the time given by a sundial, is not uniform because of the varying speed of the Earth in its elliptical orbit. Mean solar time is a uniform time that coincides with apparent solar time at four instants through the year. The difference between them is known as the equation of time, and is greatest in early November when the Sun is more than 16 minutes fast on mean solar time. Mean solar time on the Greenwich meridian is known as Greenwich Mean Time and is the basis of civil timekeeping.