January 's the first month of the year in the Julian and Gregorian calendars, and one of seven Gregorian months with the length of 31 days. The first day of the month's known as New Year's Day. It's, on average, the coldest month of the year within most of the Northern Hemisphere and the warmest month of the year within most of the Southern Hemisphere. History January's named after Janus (Ianuarius), the god of the doorway; the name has its beginnings in Roman mythology, coming from the Latin w… (More on January)