Lab
The Equation of Time
A sundial reads apparent solar time — the actual position of the sun. A clock reads mean solar time — a perfectly averaged day. The two can differ by up to 16 minutes because Earth’s orbit is elliptical (eccentricity) and its axis is tilted 23.4° (obliquity). Scrub through the year to see both components, their sum, and the figure-eight analemma the sun traces at noon.
Equation of time
+0:00
Sundial ahead (+) or behind (−) the clock
Eccentricity component
+0:00
Due to elliptical orbit
Obliquity component
+0:00
Due to axial tilt
Declination
0.0°
Sun’s angular height
Date
Day of year
Jan 1
Animation
Speed
1 day/s
Display
Sundial vs Clock