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    Re: no leap second coming in December
    From: Brooke Clarke
    Date: 2004 Jul 28, 10:34 -0700

    Hi Tim:
    There are a number of methods now used to determine the rotation of the
    The IERS is the official organization that does this.
    In the past a Photographic Zenith Tube, a telescope using a pool of
    Mercury as a reflector, looking at one star that passes directly
    overhead was used.  Today, Very Long Base Interferometery, satellites
    with corner reflectors, the corner reflector on the moon are used.
    For a year or two in the 1960s the definition of a second was changed
    each year to match the earth's rotation, but then the it was changed to
    be based on Cesium, and has been Cesium based ever since, so for the
    last 40 years or so the measurement methods have remained about the same.
    Somewhere on the web is a plot of the deviation from 86,400 seconds of
    the Earth's rotation for every day.  There's quite a bit of noise in the
    plot and a few years ago when there was an El Nino there was a big
    spike.  So weather can have a noticeable effect.  For the last couple of
    days the Earth has been hit with a large solar storm (a huge amount of
    energy has arrived at the Earth from the Sun).
    Have Fun,
    Brooke Clarke
    tjb3@IX.NETCOM.COM wrote:
    >Hi all,
    >I have been following this thread (as all others) with interest.
    >One thing I have not seen mentioned so far (unless I missed it) was the 
    possibility that the way in which the change in the Earth's rotation is 
    measured has been modified; i.e., a "better" method of determining the rate 
    of change in rotation has been implemented.  And this "better" method has 
    determined that no leap second is required this year to compensate for the 
    inaccuracies of the previous method(s).
    >I do not know how the Earth's rotation is measured to begin with, with 
    respect to leap second calculations.  So if my question is out of place, 
    please excuse the diversion.  But unless one asks....!
    >Tim B.
    >Nav-L Wallflower

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