A clock showing February 29, also known as leap day. They only happen about once every four years.
Olivier Le Moal/Getty Images
Nearly every four years, the Gregorian calendar — which is used in the majority of countries around the world — gets an extra day: February 29.
For some people, leap day means frog jokes and extravagant birthday parties. For many, it may conjure memories of the 2010 rom-com Leap Year, which harkens back to the Irish tradition by which women can propose to men on that one day. And others likely see it merely as a funny quirk in the calendar, or just another Thursday.
Leap day means several different things to Alexander Boxer, a data scientist and the author of A Scheme of Heaven: The History of Astrology and the Search for Our Destiny in Data.