A calendar is a system of organizing days for social, religious, commercial, or administrative purposes. The most common type of calendar is the Gregorian calendar, which is used in most of the world. The Gregorian calendar is a solar calendar, meaning that it is based on the Earth’s orbit around the Sun. The Gregorian calendar has 12 months, with 28 days in February in a common year and 29 days in February in a leap year.
The Gregorian calendar was introduced in 1582 by Pope Gregory XIII. It was a modification of the Julian calendar, which had been used since 46 BC. The Julian calendar had a leap year every four years, but this caused the calendar to drift out of sync with the Sun. The Gregorian calendar corrected this drift by introducing a more complex leap year rule.
