It is the winter solstice in the northern hemisphere, when the northern hemisphere is tipped furthest from the sun, resulting in the shortest amount of daylight in the year in the northern hemisphere. In the Southern Hemisphere, it would be the day with the longest amount of daylight.
December 21 2012 will be a Friday.
December 21 1978 was a Thursday.
21 December 2012 will be a Friday.
December 21, 2055 will be a Tuesday.
December 21 1951 was a Friday.
December 21 1950 was on a Thursday.
21 December 1995 was a Thursday.
December 21, 1952 fell on a Sunday.
December 21, 1962 was a Friday.
December 21 2012 will be a Friday.
December 21, 1991 was a Saturday.
December 21 2010 was a Tuesday.