The winter solstice, returning each year between December 20-22 in the Northern Hemisphere and June 20-22 in the Southern, has been a highly meaningful recurring natural event in human societies for millenia. 
The Winter Solstice Festival (Chinese: 冬至 Dōngzhì) marks the longest night in the northern hemisphere, which occurs when the Earth's north pole is tilted farthest from the Sun. Dongzhi is one of the most important festivals celebrated by the Chinese. 
After the winter solstice, consequent days will gradually become colder but increase in daylight hours, so the Chinese Winter Solstice Festival is a time for optimism and looking forward to the upcoming spring season. 
The winter solstice, which falls on a slightly different date each year, marks the shortest day in the Northern Hemisphere. 

Much like in other cultures around the world, the Chinese Winter Solstice Festival was regarded as an extremely important time and a major holiday in China. 
In fact, there is a traditional saying: “冬至大如年” (Dōngzhì dà rúnián) which roughly translates to “the winter solstice is as important as the Chinese New Year.” 
It is a day for a family reunion, a day to worship the ancestors, and a day to eat some traditional food. 
A tradition highlight for people from the northern part of China is that in northern China, people will eat dumplings  shuǐ   jiǎo [水餃] and lamb yáng ròu [羊肉] to keep warm.Wrapping dumplings together as a family is also a popular custom during the Chinese New Year (春节; chūnjié) which follows soon after the winter solstice. 
A tradition highlight for people from the southern part of China is that in southern China and Taiwan, people will eat Tang Yuán [湯圓],  
Tangyuan is typically eaten together with family and so it is considered to be an auspicious food to consume during the solstice. The character 圆 (yuán) can mean to have a reunion (团圆 tuányuán) and to be satisfactory or perfect (圆满 yuánmǎn). Therefore, eating tangyuan during the winter solstice symbolizes a harmonious, cohesive and auspicious household.