Pope Gregory XIII issues the papal bull "Inter gravissimas," on February 24, 1582, introducing the Gregorian calendar. The reform corrected a 10-day drift by skipping days in October 1582, effective on Thursday, October 4, 1582, making the following date, Friday, October 15, 1582. It was quickly adopted by much of Catholic, but not Protestant, Europe which adopted it much later.
The new Julian Calendar also aligned the vernal equinox with March 21 and introduced more precise leap year calculations to ensure long-term accuracy and fixed the date of Easter, which had drifted away from the spring equinox due to the Julian calendar's 11-minute-per-year error.
The Gregorian calendar is now widely used around the world. With the exception of Ethiopia, Nepal, Iran and Afghanistan, the Gregorian calendar is now the world's universal civil calendar, old style calendars remaining in use in religious or traditional contexts. More
