Today, we’re going to talk about a kind of travel that’s unavoidable.
As you sit reading this, though unbeknownst to you (but knownst to us), you are traveling at roughly 107,218 KM an hour (66,622 mph). Think you’re special for this? Sorry, you’re not. Everyone on planet Earth is going this fast as the Earth makes its way around the sun every second of every minute of every hour of every day of every year, to create the seasons. That’s not even taking into account the relative speed of the Earth’s rotation, but let’s keep things simple for now. Being on a living planet such as this, it was probably inevitable that the inhabitants would eventually discover just how tricky the Earth’s orbit really was, especially in the area of time. Today is Leap Day, and I’d like to share some discoveries I’ve made pertaining to it, and perhaps provide a new perspective on the mystery and intrigue of February 29th.
That Darn Julian
For the past 2000 years or so, February 29th, an inherently made up day, has been special. As of 45 BC (after Intercalaris was abolished), February 29th has been modern civilization’s answer to the inconvenient fact that the Earth only makes an orbit around the sun about every 365.24219878 days instead of a happy round number like 365. To make up for this pesky result of messy orbits, 1 day was inserted every 4 years, giving us the leap day. However, this still wasn’t close enough to the true planetary orbit, and after a while the calendar fell farther and farther out of pace with the reality of the seasons.
Time To Make Some Minor Changes
By the time Pope Gregory XIII proclaimed the aptly named Gregorian calendar in 1582, the old Julian calendar had to be adjusted a hefty 11 days forward from October 4, 1582 to October 15, 1582. (So if anyone ever tells you about October 5, 1582, you can safely tell them that it never happened. Unless they’re using dates adjusted to the Gregorian calendar, of course.) Shifting over to the Gregorian calendar was clearly a step in the right direction, and it’s the same calendar that most of the world uses today. The change was simple. In the Julian calendar, every 4th year had a leap day on February 29th. In the new Gregorian calendar, years divisible by 100 are not leap years unless they are also divisible by 400. For instance, the year 1900 was not a leap year, but the year 2000 was because 2000/400 = 500. With this new Gregorian calendar, the average length of a year is 365.2425 days, just a mere 0.00008247% off from the true orbit of 365.24219878 days. This means that the Gregorian calendar only accumulates 1 day of error every 3300 years. Not bad for a calendar approved 426 years ago.
Room for Improvement
However, there’s room for improvement. I came across a clever Swiss man named John Walker who has made an excellent point at his Calendar Converter page (which also works as a superb tool for converting between different calendar systems). John Walker discovered that the Gregorian calendar could be revised to bring the margin of error “comparable to errors due to tidal braking of the rotation of the Earth.” To do this one only has to remove any leap days from years divisible by 4000, which amounts to an average of 365.24225 days per year. According to John, this is the “equivalent to an error of one day over a period of about 19,500 years.” Can’t get much better than that.
Happy Leap Day. 
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