Time & Calendar
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Equation of Time

Difference between sundial (apparent) and clock (mean) time.

Formula

E≈9.87sin⁡2B−7.53cos⁡B−1.5sin⁡BE \approx 9.87\sin 2B - 7.53\cos B - 1.5\sin B

Variables

B360°(N-81)/364, N = day of year
EMinutes

Example

Around Nov 3 sundials run ~16 min ahead of clocks

Did You Know?

Plotting the Sun at the same clock time all year traces a figure-eight in the sky called the analemma.

sundialsolar timeastronomy