For a start, there’s the 365-and-a-quarter days it takes the Earth to orbit the sun. Then there’s the 24 hours that make up those days and the 60 minutes and seconds which fill each and every ...

But the exact time it takes is 365.2422 days, leaving us with around five hours and 49 minutes leftover each year. Every fourth year, those extra quarter-days get added to the calendar to make one ...