Why days (solar noon to solar noon) in December are longer than days in other months, From MinutePhysics. This is a result that surprises many. Our seasons, of course, are caused by the 23.5 degree tilt of the earth's axis. But, by Kepler's first law, The Earth's orbit around the sun is elliptical not circular. We are closer to the Sun in December than in June. For Earth, in obeying Kepler's second law, sweeps out an area, in December, that is equal to a similar area in June. So Earth must be traveling faster when it is closer to the Sun. This means Earth travels a greater orbital distance in the same time in December than in June. So as we pass by the Sun in December, the Earth must spin around more on its axis for us to look back to see the Sun at the same place in the sky (noon to noon). This makes the length of our day longest in December.
