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Subject: Re: Precise time
From: Richard Langley (lang@XXX.XXX)
Date: Tue Sep 03 2002 - 08:07:03 EDT
Main reason for the introduction of leap seconds is tidal friction. See
<http://www.rnw.nl/realradio/practical/html/time.html> for more information.
Studies are currently underway to examine the continuing need for leap
seconds. They may be abandoned. See GPS World, November 1999.
-- Richard Langley
Professor of Geodesy and Precision Navigation
On Tue, 3 Sep 2002, Peter Fogg wrote:
>>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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Richard B. Langley E-mail: lang@XXX.XXX
Geodetic Research Laboratory Web: http://www.unb.ca/GGE/
Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142
University of New Brunswick Fax: +1 506 453-4943
Fredericton, N.B., Canada E3B 5A3
Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/
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