Gregorian calendar

The Gregorian calendar is today's internationally accepted civil calendar and is also known as the Western or Christian calendar. The Gregorian calendar is the most widely used calendar in the world today. It is a solar calendar based on a 365-day common year divided into 12 months of irregular lengths.11 of the months have either 30 or 31 days, while the second month, February, has only 28 days during the common year.

However, every four years is a leap year, when one extra – or intercalary – day, is added on 29 February, making the leap year in the Gregorian calendar 366 days long. The Gregorian calendar's, replaced the Julian calendar because it was too inaccurate. It did not properly reflect the actual time it takes the Earth to circle once around the Sun, known as a tropical year. The Julian calendar's formula to calculate leap years produced a leap year every four years. This is too often, and eventually the Julian calendar had become 10 days out of synchrony with the solar cycle.

The Gregorian calendar was first adopted in Italy, Poland, Portugal and Spain in 1582. New formula for calculating leap years was adopted, the year is evenly divisible by 4. The more advanced leap year formula makes the Gregorian calendar far more accurate than the Julian. However, it is not perfect either. Compared to the tropical year, it is off by one day every 3236 years.

Although the Gregorian calendar is named after Pope Gregory XIII, it is an adaptation of a calendar designed by Italian doctor, astronomer and philosopher Luigi Lilio (also known as Aloysius Lilius). He was born around 1510 and died in 1576, six years before his calendar was officially introduced.

It got birth in Vatican pope Gregory VII. 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.