Equation of Time Calculator
Calculate the Equation of Time (EoT) - the difference between apparent solar time (sundial time) and mean solar time (clock time). This varies throughout the year due to Earth's orbital eccentricity and axial tilt.
Equation of Time
Equation of Time
+3m 6s
3.103 minutes
Interpretation
Sundials run 3.1 minutes FAST (sun ahead of mean time)
Contributing Factors
Eccentricity Effect
4.577 min
Elliptical orbit
Obliquity Effect
-7.082 min
Axial tilt (23.5 deg)
Solar Declination
21.3331 deg
Day of Year
148
Annual Extremes
Maximum Fast (Sundial ahead)
+16.38 min
Around day 305 (early November)
Maximum Slow (Sundial behind)
-14.26 min
Around day 45 (mid February)
When EoT = 0 (Sundial matches clock)
About the Equation of Time
The Equation of Time is the difference between apparent solar time and mean solar time. Two factors cause this variation: (1) Earth's elliptical orbit causes it to move faster at perihelion (January) and slower at aphelion (July), and (2) the 23.5 degree tilt of Earth's axis means the sun's apparent motion along the ecliptic projects onto the celestial equator at varying rates. The combination produces a maximum variation of about +/- 16 minutes throughout the year.
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Editorial Note
MyCalcBuddy Editorial Team
This page is maintained as an educational calculator reference.
Formula Source: Standard Mathematical References
by Various