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    Re: Precise time
    From: Richard B. Langley
    Date: 2002 Sep 3, 09:07 -0300

    Main reason for the introduction of leap seconds is tidal friction. See
     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.
     Richard B. Langley                            E-mail: lang@unb.ca
     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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