It has to do with the fact that the Earth orbits the sun on an inclined path to the Ecliptic, and its velocity changes depending on where it is in the orbit among other factors such as the location of the observer on the Earth. The above figure of the analemma shows that the length of day is a complicated function of the time of the year, and the figure is tilted to the left or right depending on your latitude. This makes the length of day very asymmetric about the local noon hour.
Copyright 1997 Dr. Sten Odenwald
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