Pope Gregory XIII: the man who fixed the calendar in 1582. Any ancient society that studied astronomy also worked on inventing a calendar, as well.  Not all of them got it right, but they made quite a few good efforts.  Ancient Rome spent 700 years designing and redesigning the calendar until they decided they had it right in the year 46 BCE.  They called this calendar the Julian Calendar, after Julius Cæsar, and it became the standard calendar to be used in Europe forever after. Well, not forever after, really.  Just for the next fifteen centuries, when someone noticed a mistake.  Easter, a spring holiday, seemed to keep coming later and later in the year.  Scientists studied this and realized that a miscalculation on the part of the Romans was causing the calendar to lose one whole day every 128 years.  That doesn’t sound especially dire, but by the time someone decided to do something about it, in 1582, the calendar had lost ten whole...