So, what did you do with your extra second this morning?
I had a bit of a lie-in because we were out with friends, watching a band last night, and I was slightly the better for wear (well, I thought so, others apparently thought my volume could have done with attenuating) after partaking in maybe one too many Thatcher’s Gold ciders.
That extra second in bed made all the difference.
But what’s it all about, this leap second business?
The last one, since their introduction in 1972, was added last night, at 23:59:60. This bought GMT (or UT1 as it’s now known) into line with Co-ordinated Universal Time, (UTC) which is designed to keep all time on Earth in line with solar time – the reason for there being 365ish days in the year – and make sure that an hour is an hour, wherever you are.
Graph showing difference between UTC and UT1. Leap seconds indicated by peaks.
24 hours is 86400 seconds. Earth’s rotation varies according to many geological, cosmic, and climatic factors, meaning that every now and then we have to manipulate our perception of time to ensure that there are 86401 or 86399 seconds in one particular day.
The only trouble is, the furthest in advance you can predict the need to do this is about six months, which is why leap seconds are added (or, theoretically, subtracted) at such irregular intervals. 25 seconds have been added since 1972, none taken away.
Deviation of day length from SI unit second. (1962-2010)
The largest variation in the Earth’s rotation time is caused by tidal friction which is basically, a giant centrifugal brake on the whole planet made of water, which if not adjusted for, could have added over 2 minutes per century to our perceived idea of solar time.
If you’d rather read an altogether more entertaining theory on, for instance, why Tuesday afternoons drag by so slowly, or how it is that the last hour in the pub whizzes by in no time at all, then you need to be educated about Procrastinators. Something dreamed up by Terry Pratchett for his fabulous book, Thief of Time.
Thanks to the (deep breath) International Earth Rotation and Reference System Services, we will have six months notice for the next leap second, so plan what to do with it carefully, you never know when you’ll get the next one.