Today is February 29th, which is my Great-Aunt Elane’s birthday. Despite the fact that she is my grandmother’s sister, today is only the 18th or 19th time she has actually celebrated her birthday on her birthday, because she was born on February 29th, which only comes around every 4 years.
Why do we do that? Well, according to the National Maritime Museum in the UK, the reason is because the year is not really 365 days long. It is actually 365.24219 days long, and over time, that .24219 of a day starts to add up. Actually, by 1582 this small difference had really thrown things out of whack, so that the months were not lining up with the same seasons any more. Thus, Pope Gregory the XIII implemented the Gregorian calendar that we use today.
For those of you out there who are into this sort of stuff and want to learn a bit more, I would recommend Duncan Steele’s book Marking time : the epic quest to invent the perfect calendar, which is here in the MVCC library.