January is the first month of the year in the Julian and

Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pope Gregory XIII as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years dif ...

s and is also the first of seven months to have a length of 31 days. The first day of the month is known as New Year's Day. It is, on average, the coldest month of the year within most of the Northern Hemisphere (where it is the second month of winter) and the warmest month of the year within most of the Southern Hemisphere (where it is the second month of summer). In the Southern hemisphere, January is the seasonal equivalent of July in the Northern hemisphere and vice versa. Ancient Roman observances during this month include

Cervula ''Cervulus'' or ''Cervula'' is the name of a Roman festival celebrated on the kalends of January (1 January). According to Chambers (1864), remnants seem to have been incorporated into a medieval Christian Feast of the Ass, (''Festum Asinorum''), ...

and Juvenalia, celebrated January 1, as well as one of three

Agonalia An Agonalia or Agonia was an obscure archaic religious observance celebrated in ancient Rome several times a year, in honor of various divinities. Its institution, like that of other religious rites and ceremonies, was attributed to Numa Pomp ...

, celebrated January 9, and Carmentalia, celebrated January 11. These dates do not correspond to the modern Gregorian calendar.

History

Les Très Riches Heures du duc de Berry Janvier

January (in Latin, ''

Ianuarius ''Ianuarius'', fully ''Mensis Ianuarius'' ("month of Janus"), was the first month of the ancient Roman calendar, from which the Julian and Gregorian month of January derived. It was followed by ''Fe