The traditional East Asian calendars divide a year into 24 solar terms . Dōngzhì or Tōji is the 22nd solar term, and marks the winter solstice. It begins when the Sun reaches the celestial longitude of 270° and ends when it reaches the longitude of 285°. It more often refers in particular to the day when the Sun is exactly at the celestial longitude of 270°. In the Gregorian calendar, it usually begins around December 21 and ends around January 5.
The solstices mark the ''middle'' of the seasons in East Asian calendars. Here, the Chinese character means "extreme", so the term for the winter solstice directly signifies the summit of winter, a linkage absent in Western languages.
In China, Dongzhi was originally as an end-of-harvest festival. Today, it is observed with a family reunion over the long night, when pink and white ''tangyuan'' are eaten in sweet broth to symbolise family unity and prosperity.