Why does February have 29 days every four years? When is it, why does it happen, why is 2016 a leap year? 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.
So leap seconds – and leap years – are added as means of keeping our clocks (and calendars) in sync with the Earth and its seasons.
But did you ever wonder why is February the shortest month?
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, Feb 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.
Technically, a leap year isn’t every four years. The year 2000 was a leap year, but the years 1700, 1800 and 1900 weren’t. 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.
The Roman calendar used to have 355 days with an extra 22-day month every two years until Julius Caesar became emperor in the 1st Century and ordered his astronomer Sosigenes to devise something better.
Sosigenes decided on a 365-day year with an extra day every four years to incorporate the extra hours, and so February 29th was born.
As an earth year isn’t 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 Europeans, Greeks and Romans have learnt that from ancient Egyptians who were the first to observe, discover and document the imprecise time period of earth’s orbit.
The maths has worked ever since but the system will need to be rethought in about 10,000 years’ time. Perhaps mankind’s robot overlords will think of something.
So What’s 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 last leap second was added in 2012 Mozilla, Reddit, Foursquare, Yelp, LinkedIn, and StumbleUpon all reported crashes and there were problems with the Linux operating system and programmes written in Java.
The chances of having a leap birthday are one in 1,461. People who are born on February 29 are referred to as “leaplings”, or “leapers”. In non-leap years, many leaplings choose to celebrate their birthday on either February 28 or March 1, while purists stick to February 29 for the occasion.
Some suggest those born before midday on February 29 should celebrate their birthdays on February 28, while those born in the afternoon and evening of 28 should celebrate their special day on March 1.
Those born around midday are less fortunate when it comes to picking a side. About 4.1 million people around the world have been born on February 29.