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Subject: Precise time
From: Peter Fogg (ffive@XXX.XXX)
Date: Tue Sep 03 2002 - 04:36:01 EDT
>From the local paper:
Q - How often are leap seconds added, and who decides?
A - The decision to add leap seconds to UTC (Universal Time
Co-ordinated, formerly known as Greenwich Mean Time) is made by the
International Earth Rotation Service at the Observatoire de Paris.
Because the length of a day is not exactly 86,400 seconds, the alignment
is maintained by adding or subtracting leap seconds, usually at the end
of June or December. Since 1972 there have been 22 leap seconds added,
most recently in December 1998.
Another version of this I heard was that our solar system is slowing
down, it takes ever longer for the earth to rotate on its axis - our
day, and for the earth to orbit the sun - our year; thus the need for
leap seconds to be added.
All of which reminds me of a discussion on this list some time ago about
accurate time-keepers. Someone told the story about someone else who
bought an expensive watch that kept perfect time, to the second. Then
one day it was out by one second. Naturally enough he was upset, and
eventually found that one of these leap seconds had been added. So it
seems that his watch was still keeping perfect time, unfortunately the
universe (less reliably!) was running slow.
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