The Gregorian calendar is the calendar in current use in the Western world, both as the civil and Christian ecclesiastical calendar. Instituted by Pope Gregory XIII in 1582, the calendar has 365 days with an extra day every four years (the leap year) except in years divisible by 100 but not divisible by 400. Thus, the calendar year has an average length of 365.2422 days. The Gregorian calendar replaced the Julian calendar , which had become 10 days out of synchrony with the solar cycle. In October, 1582, 10 days were dropped from the calendar. England and the American colonies were late in adopting the calendar. In 1752, they dropped 11 days.