The winter solstice is the shortest day and the longest night of the year. It is the moment when the sun is at its farthest point from the celestial equator, and the earth's North Pole is tilted furthest away from the sun. This occurs because the earth's axis is tilted relative to its orbit around the sun.
The winter solstice usually occurs on December 21 or 22 in the Northern Hemisphere, and on June 20 or 21 in the Southern Hemisphere. It marks the beginning of winter in the Northern Hemisphere and the beginning of summer in the Southern Hemisphere.
The winter solstice has been celebrated by many cultures throughout history, as it marked the return of the sun after the longest night of the year. In many cultures, the winter solstice was seen as a time of renewal and rebirth, and was celebrated with feasts, rituals, and other celebrations.