Twenty Nine Times Twelve


Today is the first time in four years that all twelve months of the year feature 29 days. Yup. Today’s a leap day. Which means anyone born on 29th February finally gets to celebrate their birthday properly. On the plus side for them, when everybody else reaches the grand old age of 80, they’ll be just starting their twenties.

So to celebrate, we thought we’d look at why we get this strange quadrennial bonus day, tacked on to the end of a winter month. But that’s not all… no, no, no… We’ll also take look at why 29 is such an interesting number…

Its the 29th of February. A rare day indeed – but if we didn’t have it, at the end of a century the calendar would be off by around 24 days. That’s because there aren’t really 365 days in a year. The Earth actually takes 365.242189 days to orbit the sun (that’s 365 days, 5 hours, 48 minutes, and 45 seconds). That gave the boffins who made up the gregorian Calendar a small conundrum. Their solution was to wait until the leftover fraction became (almost) a whole and add it in to a year. Think of it like a free data boost on your mobile phone contract, only a bit more significant.

Now you’ll probably have noticed that the additional 0.242189 of a day, when multiplied by 4, comes to a little less than 1 (11 minutes and 14 seconds to be exact). Which means there’s still another tiny bit to go, even after that extra day is added every fours years. – and that after 128 years the calendar year would have gained a whole day. Nothing in the Space Time Continuum then, appears to be uniform.

So what’s the solution to compensate for that tiny fraction? The boffins created a very clever rule, called the Calendar Correction Part II. By omitting leap years three times over four hundred years they offset the fractional difference. To equate that they decided that the century years would not leap. And to single out the 1 in 4 that would remain a leap year they decreed it should be divisible by 400. The first and last one of them was the year 2000.

But what about the number 29? It’s an interesting combination of digits…

  • It’s XXIX in Roman Numerals. 
  • The odds of being born on 29th February are 1:1461
  • It’s the 10th Prime Number (it can’t be divided by any number other than 1).
  • If you add up the consecutive squares of 2², 3² & 4² – you get 29. 
  • It’s the atomic number for Copper (Cu). 
  • It’s the name of a Ryan Adams album (and might well be the name of Adele’s next release if she sticks to her modus-operandi on naming albums!).
  • There are 29 bones making up your skull.
  • 20 is the number of years Saturn takes to orbit the sun. 
  • ‘In your prime’ – 29 is what you’ll hear if the ball is at Bingo.
  • Track 29 at a-quarter to four is where you’ll find the Chattanooga Choo Choo ready to leave Pennsylvania Station – in the Glen Millar song.

And finally, there’s one place where 29 is missing in action … there’s no M29 on the UK motorway network.


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