A consequence of the ellipticity of the Earth's track is that its orbital motion is faster near perihelion than near aphelion. This has the effect of making the day longer in Winter than in Summer: not the day from sunrise to sunset, but from one noon to the next. We keep our clocks from going haywire by the employment of the device known as mean time, thereby measuring time not by the true Sun, as does the sundial, but by a fictitious mean Sun which moves uniformly along the celestial equator, not along the ecliptic.
ASTROLABE ENCYCLOPEDIA
