Humble Pi: When Math Goes Wrong in the Real World

by Matt Parker

This goes from being a minor inconvenience to becoming a major problem because the Earth’s orbital year controls the seasons. The Northern Hemisphere summer occurs around the same point in the Earth’s orbit every year because this is where the Earth’s tilt aligns the north toward the position of the sun. After every 365-day year, the calendar year moves a quarter of a day away from the seasons. After four years, summer would start a day later. In less than four hundred years, within the lifespan of a civilization, the seasons would drift by three months. After eight hundred years, summer and winter would swap places completely. To fix this, we had to tweak the calendar to have the same number of days as the orbit. Somehow, we needed to break away from having the same number of days every year, but without having a fraction of a day; people get upset if you restart the day at a time other than midnight. We needed to link a year to the Earth’s orbit without breaking the tie between a day and the Earth’s rotation. The solution that most civilizations came up with was to vary the number of days in any given year so there is a fractional number of days per year on average. But there is no single way to do that, which is why there are still a few competing calendars around today (which all start at different points in history). If you ever have access to a friend’s phone, go into the settings and change their calendar to the Buddhist one. Suddenly, they’re living in the 2560s. M...