February 29, Leap Day, is a special day and, in its honor, we are looking at some interesting aspects of time. Previous posts have reviewed the events of Leap Day 1912 and looked at the change of the concept of time from completely analog to a standardized concept divided the world around into common time zone. Today, we look at Leap Year – why we need it, how it came about and some interesting facts about it.
Why we have it is pretty easy. We call a year 365 days. In fact it takes the Earth 365.242 days to go once around the sun, to have the calendar year balance out with the “solar” year, we would have to add about six hours to December 31. That might suit the News Years party goers, but would certainly make getting up on New Year’s Day a little iffy.
It wasn’t hard to notice that dates were getting out of whack if you were paying attention and the Romans had it all figured out. Julius Caesar had a hand in the origin of leap year in 45 BC. Before Julius, the Romans had a 355 day calendar and needed to slip in a whole extra month every couple of years to keep things straight. If this sounds strange, it wasn’t, both the Jewish calendar and the Chinese calendar have a similar approach. This likely stems from the use of lunar months to calculate the year. A year of 12 lunar months is about 354 days with the average time between full moons at 29 days, 12 hours, 44 minutes. If we operated on lunar months, every few years your Washington home insurance would have a thirteen month billing cycle.
The Romans – like folk on the peninsula – had a lot of festivals to keep track of. A couple of years of lunar month calendars and we would be doing the Rhody Run the same week as the Lavendar Festival. Julius Caesar simplified things by adding some days to different months of the year and created the 365 day calendar. Caesar established leap years as well, though likely not to delay his death on the Ides of March by a day.
So, with the year just a bit longer than 365 days, we need to catch up. We add a leap year every four years – except over a few centuries that adds too much time so on some century years we don’t have a leap year. In fact, century years are only leap years if they can be divided evenly by 400. Got that? There will be a test.
The oddity of a day that occurs once every four years is associated with other oddities. Leap Day has been known as “Bachelors’ Day,” maybe after an Irish legend that St Bridget did a deal with St Patrick to allow women to propose to men every 4 years. There is also an Honor Society of Leap Year Day Babies, a club for people born on February 29th.
Maybe the most interesting historical question though is what happened on February 30th? You never heard of February 30? In 1700, Sweden decided to change from the Julian calendar to the Gregorian calendar as other European countries had. To true up the calendars, the Swedes needed to lose eleven days. Other countries had simply dropped the necessary days in one year. Sweden decided to adjust over forty years by eliminating leap days. It turned out to be an unfortunate plan that would have had Sweden out of sync for 40 years. Sweden decided to realign in 1712 and to get everything right had to have two leap days – February 29, 1712 was a normal Leap Day and February 30, 1712 replaced the day that had been omitted in 1700.