December is Winter Solstice, the shortest day of the year in the Northern Hemisphere. In the Southern Hemisphere, conversely December 22 is Summer Solstice in places like Australia, New Zealand, or South Africa, therefore, December 22 is the year's longest day. This situation will be reversed after six months from. On June 21 , every year, the Northern Hemisphere will see the Summer Solstice when the day will be the year's longest. And the Southern Hemisphere will see the year's shortest day - or longest night.