Do know it

Do you know why we say ‘April fool’ on 1 April?

April Fool's Day, also known as All Fools' Day, is a holiday celebrated on the first of April each year. Its origins started in Europe during the Middle Ages. One theory is that it began as a result of the adoption of the Gregorian calendar in the late 16th century, which moved New Year's Day from April 1 to January 1. Those who continued to celebrate the new year on the old date were ridiculed as "April Fools."
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 been in use since the Roman Empire.

The Gregorian calendar was introduced to correct errors in the Julian calendar that had accumulated over centuries. The Julian calendar was based on a solar year of 365.25 days, which is slightly longer than the actual solar year of 365.2422 days. Over time, the calendar fell out of sync with the seasons, leading to problems with the timing of religious observances, agricultural practices, and other important events.

To correct this problem, the Gregorian calendar introduced a number of changes. It reduced the number of leap years, skipping leap years in years ending in "00" unless they were divisible by 400. It also shifted the date of the spring equinox to March 21, which had been slowly moving earlier in the year under the Julian calendar.

Today, the Gregorian calendar is used by most countries in the world for civil purposes, including the calculation of public holidays and official events. Some religious groups still use other calendar systems, such as the Islamic calendar or the Hebrew calendar, for their own purposes.