Answer: Gregorian Calendar

The time it takes the Earth to whirl around its axis and, in turn, rocket around the Sun, might be the same for all of us enjoying the ride together, but around the world there are numerous ways cultures have divided up and numbered the trip.

Among all the different calendars, however, one calendar has emerged as the de facto global standard for civil date keeping, giving all the nations of Earth the ability to engage in communication and commerce using the same reference points: the Gregorian calendar.

Named after Pope Gregory XIII, responsible for the introduction of the calendar in October 1582, the calendar wasn’t a radical introduction of a new calendar. Instead, it was a careful refinement of an existing calendar: the Julian calendar (named after Julius Caesar, who proposed the calendar in 46 B.C. as a refinement of the Roman calendar).

The Gregorian calendar, in addition to including refinements of the Catholic liturgical calendar, also involved a refinement quite important for secular calendar keeping: the modification of leap years and centuries which ensured that the Gregorian calendar remained in sync with the natural solar calendar.