Winter Solstice 2020 is today, Dec. 21, at 4:02 a.m. This is the shortest day of the year. However, it is neither the latest sunrise nor the earliest sunset. The earliest sunsets (shortest afternoons) happen about a week before the Solstice and the latest sunrises (shortest mornings) happen about a week after. The differences are miniscule, but measurable, as well as explainable.
Our clocks show a day to be 24 hours, but the sun in the sky is not so steady. The solar day, which is the time from one day to the next between the sun's peak in the sky, varies very slightly at different times of the year due to the elliptical shape of Earth's orbit around the sun. This creates very small irregularities that are displayed in these slight vagaries in sunrise and sunset times.
