By Heath Raftery

At a little after midday today, humankind will experience a remarkable moment as clocks tick over to show 12:34:56, 7/8/9.

If you want to catch it, keep your eyes glued clockwards today. It’s a performance that won’t happen again for another 100 years! If you can’t wait that long (most of us can’t, some of us can) it’s only another 80 years until today’s alignment is spectacularly surpassed, when all 10 digits will align in perfect order: 01:23:45, 6/7/89.

(Press play for your sophisticated soundtrack to this momentous day below…)

But how did we arrive at this extraordinary moment? With a great deal of rigmarole, as it turns out …

When Jesus walked the Earth 2,000 years ago we were not yet counting years anno domini (AD), and Augustus had only recently been honoured in the calendar system, renaming Sextilis to August. But the calendar of the time, the Julian calendar (named for Julius Caesar), was quite accurate by today’s measures. Astronomers had correctly approximated the period of seasonal variation over the year to 365 days and even accounted for most of the inaccuracy by adding an extra day to February every four years. Don’t forget, this was 1,600 years before Galileo Galilei managed to get arrested by vehemently arguing the Earth revolves around the sun!

In fact it took until Galilei’s time for the Julian calendar to be surpassed. On the 24th of February, 1582 (by our current calendar), Pope Gregory XIII decreed the Gregorian calendar and it became the internationally accepted civil calendar we still use today (although there are plenty of creative variations on how to present it).

Most of Europe at that time was already using the Incarnation of Jesus as an epoch for counting the years, and the main reform introduced by the Gregorian calendar was to further refine the inaccuracy of leap years by specifying the “don’t leap if divisible 100, except if also divisible by 400″ condition we use today.

So, in a world where people mostly still believed the sun revolved around the Earth, astronomers were able to measure the yearly period to 365.2425 days. Not bad, considering we now know the earth actually takes between 365.2421 and 365.2596 days to orbit the sun.

That brings us to 2008 AD which places us at Day 733407.

The origin of a month is suggested by its cognate, Moon. Indeed, a month arose as a measure of the cycle of moon phases. The irregular lengths of the months we use today, however, are less a measure of astronomical behaviour and more a product of variously motivated adjustments over a long and vague history. The variation from astronomical behaviour is particularly evident in February, which can pass without a single full moon occurring. Our modern month lengths were set way back in 45 BC with the introduction of the Julian calendar, and August became the eighth month instead of the sixth several hundred years prior.

August 2008 places us at Day 733619.

Even before it was well understood that the Earth undergoes rotation, it was clear to astronomers that the pattern of stars above them repeated with some regularity, and the period of a day could be measured. The day then, has historically formed a useful fundamental measure of time, from which other units such as the year and the hour, could be defined.

The 8th day of August brings us to Day 733627.

The hour was chosen in ancient civilisations as a convenient way to section a day, and the most logical division of the time was twelve. The period between sunrise and sunset was therefore split into twelve hours, and a full day became 24 hours. Most people now would assume dividing by ten would have been more logical. Perhaps they’re right, but when the seasonal variations of the year are marked by twelve cycles of moon phases, and all your life you’ve been counting to twelve on one hand by tapping your thumb against each of the phalanges of your other four fingers, you may well think otherwise.

The 12th hour on the 8th day puts us at hour 17606867 AD.

The Babylonians recognised the number 60 as being particularly suitable for arithmetic, given it is divisible by 2, 3, 4, 5, 6 and 10, and did their astronomical calculations in the sexagesimal (base-60) system. It is from them that our divisions of the hour – the minute and the second – arise.

The 34th minute of the 12th hour puts us at minute 1056412028 AD, and finally, the 56th second of the 34th minute places the historical event of 12:34:56 on the 7th August, 2009 at the 63384721712th second, anno domini.

But what does 63384721712 represent?

Well, that many 5 cent coins would weigh more than four and half Sydney Harbour Bridges, yet if you placed all those coins end to end you’d still only be one hundredth of the way to the Sun.

In other words, large numbers are terribly hard to comprehend. This is why scientists use a variety of units – instead of the Sun being 6338472171200 coins away, it’s 1 AU (astronomical unit) away. Instead of the Sydney Harbour Bridge weighing 14085493713 coins, it weighs 36 kilotons.

The units we use to tell the date might be a hodge-podge of millennia-old decisions, but they sure are a great deal better than keeping track of 63384721712 seconds!

If maths tickles your fancy, try typing in ‘maths’ to the search bar on this blog and check out some of the maths-related events happening as part of National Science Week. Including this event: ‘Mathematics and Sex with Clio Creswell‘.

Tags: calendar, maths, time

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