January (i/ˈdʒænjuːˌɛəri/ JAN-yoo-AIR-ee) is the first month of the year in the Julian and Gregorian calendars and one of seven months with the 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.January starts on the same day of the week as October in common years, and starts on the same day of the week as April and July in leap years. January ends on the same day of the week as February and October in a common year, and ends on the same day of the week as July in a leap year. In all years, January begins and ends on the same day of the week as May of the previous year. January in common years immediately before other common years begins on the same day of the week as April and July of the following year and in leap years and years immediately before that, January begins on the same day of the week as September and December of the following year. In common years immediately before other common years, January finishes on the same day of the week as July of the following year while in leap years and years immediately before that, January finishes on the same day of the week as April and December of the following year.