Why Are There Leap Years?

There are leap years because the time it takes for Earth to complete one orbit around the Sun is not a whole number of days. Earth goes around the Sun every 365.2422 days. The remaining 0.2422 day is pretty close to one-quarter of a day (0.25), so an extra day—February 29—is usually added every four years. This was first done with the Julian calendar in 46 bce, giving an average year length of [(3 ⨉...