Gregorian Reform

The Gregorian Reform was an important religious change that happened in 1582. It was a change to the calendar – the way we count the days. Before this change, people were using a calendar called the Julian Calendar. The Julian Calendar added an extra day to certain months every four years, which made it longer than the actual amount of time it takes the Earth to go around the Sun. This meant that each year using the Julian Calendar was a bit longer than the real length of a year.

But a longer calendar year means that special days like holidays happen at different times than they should. So a group of people, led by something called the Pope Gregorian Reform fixed this problem. They changed the calendar so that it was closer to the actual length of the year.
They also changed the way the days and months are counted, so that they match up better with the Sun and the real length of a year. This is why we now use the Gregorian Calendar. Now special days like holidays happen at the same time each year, and we can track time more accurately.