The equation of time and the analemma

Abstract

The Earth's progress around the Sun varies through the year. Combined with the tilt of the axis of rotation, this results in variations of the length of a solar day. The variations are encapsulated in the Equation of Time. A plot of altitude versus az-imuth for the Sun at 12 noon local time through the year describes a figure-of-eight curve known as an analemma. By analysis of the observations, we find that the qualitative aspects of the analemma can be reproduced using just two sinusoidal components.