equation of time
  • noun the time that must be added to mean solar time, as given by a clock, to make it equal to apparent solar time, as given by a sundial
  • The difference, of a few minutes at most, between noon and the time at which the Sun reaches the meridian on a particular day. The difference is a consequence of the eccentricity of the Earth’s orbit, which prevents the Earth’s rotation and its orbital motion from remaining in perfect step.

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