Gregorian calendar

The Gregorian calendar is the most widely used calendar system in the world today. It was introduced by Pope Gregory XIII in 1582 as a reform of the Julian calendar, which had become out of sync with the solar year. The Gregorian calendar is a solar calendar, based on the Earth's orbit around the sun, and consists of 12 months with varying numbers of days. It also includes leap years to adjust for the 365.2425 days it takes for the Earth to orbit the sun. The adoption of the Gregorian calendar was not immediate, with some countries, including Great Britain and its colonies, resisting the change for several centuries. However, it eventually became the standard calendar in most of the world due to its accuracy in tracking the seasons and religious holidays.