22nd December 2017 is known as Dongzhi Festival (冬至) to the Chinese. It is the shortest day of the year—the winter solstice
Dōngzhì is the day when families get together and eat tāng yuán (汤圆/湯圓), a sweet soup made of glutinous rice balls which symbolise reunion. The tang yuan is also placed on altars as offering to the deities and the ancestors. The festive food is also a reminder that celebrators are now a year older and should behave better in the coming year. Even today, many Chinese around the world, especially the elderly, still insist that one is "a year older" right after the Dongzhi celebration instead of waiting for the lunar new year.
The origins of this festival can be traced back to the yin and yang philosophy of balance and harmony in the cosmos. After this celebration, there will be days with longer daylight hours and therefore an increase in positive energy flowing in. The philosophical significance of this is symbolized by the I Ching hexagram fù (復, "Returning").