Why do we have leap years?
A leap year, where an extra day is added to the end of February every four years, is down to the solar system’s disparity with the Gregorian calendar. A complete orbit of the earth around the sun takes exactly 365.2422 days to complete, but the Gregorian calendar uses 365 days. Leap seconds – and leap years – are added as means of keeping our clocks (and calendars) in sync with the Earth and its seasons.
Why does the extra day fall in February?
All the other months in the Julian calendar have 30 or 31 days, but February lost out to the ego of Roman Emperor Caesar Augustus. Under his predecessor, Julius Caesar, February had 30 days and the month named after him – July – had 31. August had only 29 days. When Caesar Augustus became Emperor, he added two days to ‘his’ month to make August the same as July. So, February lost out to August in the battle of the extra days.
The Roman calendar did have 355 days with an extra 22-day month every two years, until Julius Caesar became emperor and ordered his astronomer Sosigenes of Alexandria to devise a better system in the 1st Century. Sosigenes decided on a 365-day year with an extra day every four years to incorporate the extra hours, and so February 29th was created.
As an earth year is not exactly 365.25 days long Pope Gregory XIII’s astronomers decided to lose three days every 400 years when they introduced the Gregorian calendar in 1582. The precise arithmetic has never quite worked ever since and the system will need to be rethought one of these decades.
Technically, a leap year isn’t every four years
The year 2000 was a leap year, but the years 1700, 1800 and 1900 were not. There’s a leap year every year that is divisible by four, except for years that are both divisible by 100 and not divisible by 400. The added rule about centuries (versus just every four years) was an additional fix to make up for the fact that an extra day every four years is too much of a correction.
What is a leap second?
Leap years are not directly connected to leap seconds, but both are for the purpose of keeping the earth’s rotations in line with our clocks and calendars. Leap seconds are added to bring the earth’s rotation into line with atomic time. A leap second was added at the end of June last year, when immediately before midnight dials read 11:59:60.
Atomic time is constant, but the Earth’s rotation is gradually slowing down by around two thousandths of a second per day. Leap seconds are therefore crucial to ensuring the time we use does not drift away from time based on the Earth’s spin. If left unchecked, this would eventually result in clocks showing the middle of the day occurring at night.
The extra second can sometimes cause problems for some networks which rely on exact timings. When a leap second was added in 2012 Mozilla, Reddit, Foursquare, Yelp, and LinkedIn, all reported crashes.
Random Facts about Leap Years
- The Summer Olympic Games are always held in a leap year. This year, they take place in Rio de Janeiro, Brazil.
- US presidential elections are held every four years, in a leap year.
- In Greece couples often avoid getting married in a leap year, believing it to be bad luck
- Food for thought: If you work on a fixed annual wage, February 29th is just one more day’s work than you would usually have to do for your salary.
- February 29 also marks Rare Disease Day.
- Leap years are also known as intercalary or bissextile years.
- In 1940, Hattie McDaniel became the first black person to win an Oscar for her role as Mammy in Gone with the Wind.
With the 29th falling on a Monday this year, I think it is likely that most of us will be spending Leap Day at work this year (which also coincides with the RRSP Contribution Deadline). At least we have the Olympic Games to look forward to – as of the 29th, there will be 158 days until the Opening Ceremonies.