The Gregorian calendar, also known as the Western or Christian calendar, is the most widely used calendar in the world today. Its predecessor, the Julian calendar, was replaced b… See more

Over the centuries since its introduction in 45 BCE, the Julian calendar had gradually drifted away from astronomical events like the vernal equinox and the winter solstice. To make u… See more

The papal bull issued by Pope Gregory XIII in 1582 decreed that 10 days be skipped when switching to the Gregorian calendar. However, only five countries adopted the new calend… See more

In total, more than three centuries passed until the Gregorian calendar had been adopted in all countries, from 1582 to 1927. The table below shows when the calendar reform occ… See more

The delay in switching meant that countries followed different calendar systems for a number of years, resulting in differing leap year rules. In the Gregorian calendar, most years that … See more