December

December is the 12th and final month of the year in the Julian and Gregorian calendars. Its length is 31 days.
December's name derives from the Latin word decem because it was originally the 10th month of the year in the calendar of Romulus, which began in March. The winter days following December were not included as part of any month. Later, the months of January and February were created out of the monthless period and added to the beginning of the calendar, but December retained its name.
December is the first month of winter in the Northern Hemisphere and the first month of summer in the Southern Hemisphere.
In Ancient Rome, as one of the four Agonalia, this day in honor of Sol Indiges was held on December 11, as was Septimontium. Dies natalis was held at the temple of Tellus on December 13, Consualia was held on December 15, Saturnalia was held December 17–23, Opiconsivia was held on December 19, Divalia was held on December 21, Larentalia was held on December 23, and the dies natalis of Sol Invictus was held on December 25. These dates do not correspond to the modern Gregorian calendar.
The Anglo-Saxons referred to December–January as Ġēolamonaþ. The French Republican Calendar contained December within the months of Frimaire and Nivôse.

Astronomy

December contains the winter solstice in the Northern Hemisphere, the day with the fewest daylight hours, and the summer solstice in the Southern Hemisphere, the day with the most daylight hours. December in the Northern Hemisphere is the seasonal equivalent to June in the Southern Hemisphere and vice versa. In the Northern hemisphere, the beginning of the astronomical winter is traditionally 21 December or the date of the solstice.
Meteor showers occurring in December are the Andromedids, the Canis-Minorids, the Coma Berenicids, the Delta Cancrids, the Geminids, the Monocerotids, the Phoenicids, the Quadrantids, the Sigma Hydrids, and the Ursids.