Leap Seconds
Today is the longest day of the year. I don't mean that it has the most hours of sunlight (which was either on the 21st June or the 21st December depending on which hemisphere you live in) but that the day and night combined is going to last a period of 24 hours and 1 second.
As the Earth Slows down our days are going to get longer and longer. Every century we gain about 1.7 milliseconds on average. However, it does so erratically and already the length of a day is considerably more than the 86400 seconds it should be. In order to keep time, the international scientific community has started adding on extra seconds at the end of either the last day in June or the last day in December. Due to geological uncertainty, this can't be predicted more than a year in the future; it is too much of a chaotic system. Here's a list of all the extra seconds we have accrued since we started the scheme back in 1972:
| Year | Jun 30 | Dec 31 |
|---|---|---|
| 1972 | 1 | 1 |
| 1973 | 0 | 1 |
| 1974 | 0 | 1 |
| 1975 | 0 | 1 |
| 1976 | 0 | 1 |
| 1977 | 0 | 1 |
| 1978 | 0 | 1 |
| 1979 | 0 | 1 |
| 1980 | 0 | 0 |
| 1981 | 1 | 0 |
| 1982 | 1 | 0 |
| 1983 | 1 | 0 |
| 1984 | 0 | 0 |
| 1985 | 1 | 0 |
| 1986 | 0 | 0 |
| 1987 | 0 | 1 |
| 1988 | 0 | 0 |
| 1989 | 0 | 1 |
| 1990 | 0 | 1 |
| 1991 | 0 | 0 |
| 1992 | 1 | 0 |
| 1993 | 1 | 0 |
| 1994 | 1 | 0 |
| 1995 | 0 | 1 |
| 1996 | 0 | 0 |
| 1997 | 1 | 0 |
| 1998 | 0 | 1 |
| 1999 | 0 | 0 |
| 2000 | 0 | 0 |
| 2001 | 0 | 0 |
| 2002 | 0 | 0 |
| 2003 | 0 | 0 |
| 2004 | 0 | 0 |
| 2005 | 0 | 1 |
| 2006 | 0 | 0 |
| 2007 | 0 | 0 |
| 2008 | 0 | 1 |
| 2009 | 0 | 0 |
| 2010 | 0 | 0 |
| 2011 | 0 | 0 |
| 2012 | 1 | 0 |
| 2013 | 0 | 0 |
| 2014 | 0 | 0 |
| 2015 | 1 | 0 |
| 2016 | 0 | 1 |
Normally when a clocks ticks past midnight it goes from 23:59:59 to 00:00:00. However leap seconds add an extra second which should be designated 23:59:60 in between these times.
The clock at the top of Elizabeth Tower which controls Big Ben is finely adjusted by placing old pennies on part of the balance which slow it down by 2/5s of a second in a 24 hour period. The timekeepers at the tower will ensure that the chimes of the Ben should have slowed down a second by the end of play today.
Meanwhile, the engineers at Google have been lengthening each second on their clock by 1/86400th of a second each; so that they will have the normal number of seconds, but just longer ones. Some computers automatically update; but most do not.
Have an extra long, extra special day!
