Saturday, December 31, 2005
How many seconds are there in a minute?
Normally there are 60, of course, but occasionally there are 61.
There are 61 seconds in the last minute of 2005, for example.
Which runs like this...2005 December 31 23h 59m 58s
2005 December 31 23h 59m 59s
2005 December 31 23h 59m 60s
2006 January 01 00h 00m 00s
2006 January 01 00h 00m 01s
This unusual situation arises because a leap second is being inserted tonight, just before midnight. Yes, there'll be 7 pips instead of 6, yes Big Ben will be delayed by a second and yes, by tomorrow morning your watch will be running very slightly fast. Leap seconds are added just before midnight GMT, when required, and only ever on December 31st or June 30th. They're also very rare - tonight's is the first leap second since 1998 (and only the 23rd since the first in 1972). Tiny temporal adjustments are necessary because tidal friction is causing our days to lengthen, albeit imperceptibly, and these occasional extra seconds keep Co-ordinated Universal Time (UTC) in line with the rotation of the Earth. The true explanation is rather more complicated than all that, of course (for example, GPS devices use a slightly different timescale established in 1980 that is now running 13 seconds ahead of UTC). [Readable explanations here and here] [Techie stuff here, here and here]. But whether all of this makes sense or not, just remember that you're going to have to wait one second longer for the start of next year. Have a great 2006 (when it finally arrives)!
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