equation of time
noun phrase
: the difference between apparent time and mean time usually expressed as a correction which is to be added to apparent time to give local mean time
The Equation of Time is the difference between your local apparent solar time, when the Sun crosses your meridian, and local mean solar time, which is the average rate of solar time used in clocks. Because the Earth travels at varying speeds as it traverses its elliptical orbit, the difference can be as much as 16 minutes.—
Kathleen Hill Zeller
Kathleen Hill ZellerExamples of equation of time in a Sentence
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The movement, with an 80-hour power reserve and a frequency of 4 Hz, is also home to a perpetual calendar and an equation of time display, showing the difference between mean solar time, shown on the main dial, and true solar time, which fluctuates due to the Earth’s elliptical orbit.
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Nicole Hoey,
Robb Report,
26 June 2026
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Nicole Hoey,
Robb Report,
26 June 2026
Cite this Entry
“Equation of time.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/equation%20of%20time. Accessed 6 Jul. 2026.
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