The winter solstice is the earliest one in 24 solar terms, and the time is between1February 2 1 day-23rd every year. The ancients believed that since the winter solstice, the sun be the spirit of heaven and earth began to flourish and become stronger, representing the beginning of the next cycle, which is a good day. Therefore, later, during the Spring Festival, customs such as ancestor worship and family dinners often appeared in the winter solstice. The winter solstice as a festival originated in the Han Dynasty, flourished in the Tang and Song Dynasties, and has been in existence ever since.

On the day of the winter solstice, the sun moves to 270 degrees of the yellow meridian, and the position of the sun directly on the ground reaches the southernmost point of the year, and the sun is almost directly on the Tropic of Capricorn. Therefore, the winter solstice is the shortest day of the year in all parts of the northern hemisphere, and the farther north it is, the shorter the day is.

The ancients divided the winter solstice into three stages: "One stage is earthworm knot; Second, wait for the elk horn solution; Waiting for the water to spring. " Legend has it that earthworms are creatures with yin bending and yang stretching. At this time, yin is still very strong, and earthworms in the soil are still curled up. The ancients thought that elk's horns were facing the afterlife, so they were yin, while the winter solstice was a sunny day, and the elk felt the yin gradually retreat and solved the horn; Because the yang is born, the spring water in the mountain can flow and be warm at this time.