冬至 Winter Solstice
It has been pounded into my head time and time again that December 21 is the shortest day of the year. But since I am usually thinking about things within 3 different time zones, I wondered which time zone actually gets the shortest day of the year. Since December 21 on the Asian side of the International Date Line is December 20 on the other side, and if you happen to be on the Americas side of the line, then it would be December 22 in Asia.
It begins when the Sun reaches the celestial longitude of 270° and ends when it reaches the longitude of 285°. However, it is usually referred to as the day the Sun is exactly at 270°. In the west that tends to be December 21 (sometimes the 22nd), but in East Asia it is actually on December 22.