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
-12m 60s
-12.996 minutes
Interpretation
Sundials run 13.0 minutes SLOW (sun behind mean time)
Contributing Factors
Eccentricity Effect
3.566 min
Elliptical orbit
Obliquity Effect
9.726 min
Axial tilt (23.5 deg)
Solar Declination
-17.6134 deg
Day of Year
31
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.