Winter solstice, also known as Dongzhi in Chinese, is the 22nd solar term on the Chinese lunar calendar, and it falls on December 21 this year. 

The day sees the shortest daytime and the longest night. Winter solstice marks the beginning of a period known as Shujiu Hantian in Chinese, which is believed to be the coldest 81 days that could be divided into nine units, "nine days" each.

Watch this video provided by Weather China, the online weather service of the China Meteorological Administration, to find out more.

For more: 

24 solar terms in nature: Major Snow

24 solar terms in nature: Minor Snow

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