Why doesn the earliest sunset occur on the shortest day of the year?
Is the fact that the Earth is at perihelion in January have anything to do with the phenomenon? Our clocks are synchronized with the “mean solar day”, which is the motion of the Sun if the tilt of the Earth’s axis (or obliquity) is zero and the orbit of Earth were perfectly circular (ie. zero ellipticity). So, first let us consider the case when the obliquity and ellipticity are zero. Then, the ecliptic (the plane of the solar system and the path of the Sun in the sky with respect to the stars) will coincide with the celestial equator. As the clock is perfectly synchronized with the Sun, it will always be on the meridian at 12:00 pm. But actually the Earth’s axis is tilted at 23.5 degrees. Hence, the ecliptic is tilted with respect to the celestial equator by 23.5 degrees. So what happens? Consider the fall equinox point. If the obliquity were zero, from day to day the Sun would move along the celestial equator (this is the motion due to Earth’s revolution around the Sun not due to the
