A Simple Derivation of the Equation of Time

Abstract

The equation of time is the difference between the apparent (sun observed) time and the modern day uniform time. This paper explains what causes the Equation of Time to arise. It is shown that it arises from the Earth orbit ellipticity and its axial obliquity relative to the ecliptic (the orbit plane). The paper then derives its computing equations and compares the alternative algorithms for performing these computations. It also provides physical interpretation to its causes.