This occurs (Dec 21 or 22) when one of the Earth's poles has its maximum tilt away from the Sun. The winter solstice is the day with the shortest period of daylight and longest night of the year, when the sun is at its lowest daily maximum elevation in the sky.
At this lowest point, the Sun stops its journey southward. For three days, December 22nd, 23rd , and 24th, the Sun rises on the exact same latitudinal (declination) degree.
This is the only time in the year that the Sun actually stops its movement Northward or Southward in our sky. On the morning of December 25th the Sun moves one degree northward beginning its annual journey back in the Northern Hemisphere,
The Sun seems to stop for 3 days before it starts its movement again on December 25 (Christmas). What a coincidence. This typically where the concepts of the birth or rebirth of sun gods have been common and, in cultures which used cyclic calendars based on the winter solstice, the "year as reborn" was celebrated (Resurrection?).
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