Apparent & Mean Sun

Demonstrate an understanding of the terms 'apparent Sun' and 'mean Sun'

Sun time, or apparent solar time, is the time the Sun shows in the day. Normally we can make a sundial to tell this.

Mean solar time is the time on our watches that humans have invented as Sun time is an unreliable way to tell the time.

Because of the Earth's elliptical orbit and the axis of Earth, apparent solar time as told on a sundial can be inaccurate to as much as 16 minutes. Apparent Midday on a sundial in Bristol will occur at a different moment to apparent Midday in London.


  • Apparent = 'Real Sun time'
  • Mean = ' Human time'

Caused by...

  • Earth's elliptical orbit
  • Axis of Earth

Why does society follow a mean sun time system rather than an apparent one?