December 21 (or December 22) is the shortest day of the year in the Northern Hemisphere. On this day, known as the winter solstice, the Sun in the sky is the farthest south and travels the shortest path through the sky. Therefore the day has the least daylight and the longest night. In the Southern Hemisphere, the shortest day is on June 20 or 21, when the Sun is the farthest north. After the winter solstice, the days begin to get longer.