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Equation of Time
The Equation of Time is a measure of the difference between mean (or clock) time and true (or solar time). During the year the sun's apparent motion speeds up and slows down due to:- the elliptical nature of the earth's orbit,
- the inclination of the axis of the earth's rotation, and
- the perturbations of the moon and the other planets.
The Equation of Time is True Sun Time-Mean Sun Time.
Since 1930 and a decision of the International Astronomical Union
the Equation Of Time has been measured with a positive maximum in November.The Equation of Time is measured in degrees, and may be converted to minutes by multiplying by 4. (1 degree = 4 minutes of time.)
Calculate it!
The Sun API provides the sdxEOT function to calculate the Equation of Time. The sdxFindAnnFeatx function calculates the times of annual maximum, minimum and the 4 zero crossings of the Equation of Time.