Ancient emperors offered sacrifices at the vernal equinox, summer solstice, autumn equinox and winter solstice respectively.

Sacrifices are needed at the vernal equinox, summer solstice, autumn equinox and winter solstice.

The "vernal equinox" is both a solar term and a festival, with a series of sacrificial ceremonies. In ancient times, there were ceremonies to worship the sun in spring and the moon in autumn. In the Qing Dynasty, Pan Rongbi's "Ji Sheng at the Age of Emperor Jingdi" recorded: "The vernal equinox and autumn are the grand ceremonies of the country, and scholars should not sacrifice them at will."

"Summer solstice" was once an important folk festival, which was as lively as the Dragon Boat Festival. On that day, the emperor will hold a ceremony to worship the land to pray for a bumper harvest. "It's just that with the appearance of the Dragon Boat Festival, many customs have been moved."

The autumnal equinox used to be the traditional "Festival of Sacrificing the Moon". According to textual research, the first Mid-Autumn Festival (Mid-Autumn Festival) is set on the day of the autumnal equinox, but there may not always be a full moon because of the different dates of August in the lunar calendar every year. And the moon without the moon is a big spoil the fun. Therefore, the Mid-Autumn Festival was later transferred from the Equinox to the Mid-Autumn Festival.

During the Tang and Song Dynasties, the solstice in winter was the day to worship the heavens and ancestors, and this custom has continued among the people to this day. It is a firm custom to sweep graves to worship ancestors on the solstice in winter.