Next Thursday, as you probably already know, is a leap day. We’ve been having one every four years since 45 BC, when Julius Caesar tried to put some order into the passage of time by neatly dividing each year into 12 months and 365 days. Inconveniently, the time it takes for the Earth to complete one orbit around the sun is actually a little longer than 365 days, and every four years those extra few hours add up to another whole day. Hence our need for the occasional February 29th. Like the one coming our way on Thursday.