This note accompanies the follow episode(s):
The Writer’s Almanac for October 4, 2017: Defiance

October 4, 2017: on this day: Pope Gregory XIII corrects the Julian calendar

In 1582, Pope Gregory XIII declared that the day following October 4, 1582, would be Friday, October 15, 1582. By leaping over 10 days, the pope corrected the Julian calendar, which was 10 days out of sync with the seasons. The new calendar became known as the Gregorian calendar.