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equation of time
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equation of time

astronomy
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Quick Summary

The equation of time is the difference between apparent solar time and mean solar time. Apparent solar time is what a sundial measures, based on the actual position of the Sun. Mean solar time is what clocks and watches keep, assuming the Sun moves at a constant speed.12

This difference arises because the Earth's orbit around the Sun is elliptical, causing its speed to vary throughout the year. Additionally, the tilt of Earth's axis affects how we perceive the Sun's movement. The equation of time is a correction, usually no more than 16 minutes, that is added to or subtracted from apparent solar time to get mean solar time. Since 1972, the time in common use is Coordinated Universal Time (UTC), which combines solar and atomic time.231

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
5 Britannica Sources
  1. solar time
  2. equation of time
  3. Why Is Earth’s Axis Tilted?
  4. time - Variations in the Earth’s rotation rate
  5. time - Relativistic effects

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