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Leap Year - The Longest Collaboration

February 29, 2016

Leap Year - The Longest Collaboration

Happy Leapday! You know it must be a special day if it only comes once every four years, but what you probably don’t know is that February 29th is the result of one of the world’s longest problem-solving collaborations. Long before your google calendar existed, the Ancient Egyptians were actually the first to create a system that had 365 days in the year. For all of their mathematical and astronomical prowess, however, there was a critical catch: the earth actually takes 365 days, 5 hours, 48 minutes, and 46 seconds to rotate around the earth, so over time the seasons became rather out of sync with with the Egyptian calendar.

Next up was Julius Caesar, who, in an effort to fix the disjunction ordered that an extra 24 hours be added to February 24th every four years. The rationale for this date was that February was the last month of the year. Since the last five days of the year were a time of feasting, Caesar knew that an extra 24 hours of revelry wouldn’t encounter much in the way of opposition.

The extra 24-hours helped, but the Julian calendar was still 11 minutes too long. In 1582, Pope Gregory XIII assembled a team to fix the problem, and they corrected the calendar by removing a leap day once every four centuries, eliminating the slight seasonal drift in the Julian calendar. We still use the Gregorian calendar today.

Despite our best efforts, we’ll have to make updates again one day. The reason? The earth’s rotation is still slowing. In fact, a modern day is 1.7 milliseconds longer than century ago, meaning that the good people of Downton Abbey had approximately 1.7 milliseconds less to their day. How on earth did they fit it all in?