Put your New Year celebrations on hold, just for a second

Are you looking forward to seeing in the New Year? Well, you will have to wait a bit longer than you may have expected. A leap second will be added at midnight on 31 December 2016 to keep atomic clocks in sync with the Earth’s rotation.

Universal Coordinated Time is based on super-accurate atomic clocks and it is extremely regular. We need its accuracy to enable satellites to hold their positions precisely and enable telecommunications and satellite navigation. Greenwich Mean Time, meanwhile, is based on the Earth rotating on its axis, with each spin being one solar day. The problem is that our planet’s rotation is gradually slowing down, so the length of  a day gradually increases. So, to keep everything in sync, leap seconds are occasionally added to Universal Coordinated Time.

People can get very excited about changes to timing and calendar. Many of my friends made a tidy sum proofing computers against the millennium collapse that would surely happen when the internal clocks of the world’s computers and electronic devices rolled over from a number ending 99 to one ending 00.  One cannot but draw the parallel to the hundreds of people who flocked to monasteries across Northern Europe in the Year 999. The church benefited from massive donations as penitents sought forgiveness for their sins in advance of what they wrongly feared would be the world’s end.

Of course, you don’t need a conflict between atomic and sidereal time (that’s time reckoned from the motion of a planet relative to the distant stars, rather than the Sun) to cause time-keeping problems. A year is measured as the time the Earth takes to orbit the Sun once and this can be defined in a number of ways, each of which has a slightly different value. Unfortunately these do not fit well with the length of a day, which is the time taken for the Earth to rotate once on its axis. A solar year is composed of  365 days, 5 hours, 49 minutes and 16 seconds (≈365.24255 days). So a simple solar calendar will gain about a day every four years (which is why we have leap years), or about a month a lifetime. So within six generations of an uncorrected calendar we would be sunbathing on Christmas Day and sledging in the middle of July.

Pope Gregory XIII in an early 17th century engraving

Pope Gregory XIII in an early 17th century engraving

Julius Caesar introduced the first reform which was to add a leap day in February once every four years – the Julian calendar. Much better! But it still leaves an error of around three extra days added every four centuries. The mechanism to correct this was not recognized until the 16th century when Pope Gregory X111 instituted reforms – the Gregorian calendar. However, these reforms weren’t adopted in Protestant England until 1752 when 2 September was followed immediately by 14 September to make up for the gradual slipping, all in one go. This resulted in much disquiet and many people thought their lives had actually been shortened by 11 days, but despite the urban myths, there were no Lost Day Riots in the UK.

This New Year’s Eve, rather than fear the leap second, take fun in adding a zero at the end of your countdown before you mark the start of 2017!

Image credit:
Pope Gregory XIII https://en.wikipedia.org/wiki/Gregorian_calendar


Noel Jackson

About Noel Jackson

Hi, I’m the Head of Education at Life and I am insanely curious (as well as curiously insane) about most things that make the universe tick. I love science and maths because they are the best way to explain and model the world we live in.
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