Astronomy has been a concern for the ancient Chinese. It is interesting to look at how they developed a culture for astronomy and astrology. 2500 years ago they were observing movements of the sun with a sundial. This is how they determined the point of Winter Solstice, the time being 21 or 22 of December. As ancient Chinese thought, the yang, or muscular, positive things will become stronger after this day, so it should be celebrated.
The Winter Solstice became a festival during the Han Dynasty (206 BC-220 AD).
They were organizing celebrating activities. Both officials and common people would have a rest and the army was stationed in, frontier fortresses closed and business and traveling stopped.
In the Tang and Song dynasties, the Winter Solstice was a time for honoring the ancestors. As the emperors would worship the Heaven in this day, common people offered sacrifices to their deceased relatives.

The Winter Solstice is nowadays a time of family gathering. Some say that if you eat dumpling soup on this day, it will keep you from frosting in the upcoming winter. In parts of South China, the whole family will get together to have a meal made of red-bean and glutinous rice to drive away ghosts and other evil things. In other places, people also eat tangyuan, a kind of stuffed small dumpling ball made of glutinous rice flour. The Winter Solstice rice dumplings could be used as sacrifices to ancestors, or gifts for friends and relatives. The Taiwan people even keep the custom of offering nine-layer cakes to their ancestors. They make cakes in the shape of chicken, duck, tortoise, pig, cow or sheep (each with its own significance) with glutinous rice flour and steam them on different layers of a pot. People of the same surname or family clan gather at their ancestral temples to worship their ancestors in age order. After the sacrificial ceremony, there is always a grand banquet.