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    Re: Delta-T
    From: Omar Reis
    Date: 2004 Dec 6, 12:20 -0200

    >>Of DeltaT, Omar R wrote:
    >>"I wonder why can't this value be deterministic, like everything else in
    astronomy ?"
    >Frank Reed wrote:
    >Can you predict the dust storms on Mars? How about the shape of the next
    sunspot? You would probably counter that those things are "weather" not
    astronomy. And I think that's basically how we define traditional
    computational astronomy. Anything that is subject to computation in the
    foreseeable future, we count in, otherwise it's out. Changes in delta-T
    derive from the complexities of the Earth's weather and its interior,
    channeling angular momentum from one part of the total system to another.
    The net angular momentum of the Earth, if we could measure it, presumably
    shows a much more "deterministic" decline since it's under the influence of
    the luni-solar tides. But even there, the exact damping effect depends on
    the shapes of the ocean basins (which are changing on a geological time
    I was talking about positional astronomy. I guess
    it is the closest thing to the deterministic world that
    Newton imagined in his natural philosophy.
    A few sciences can make predictions a thousand
    years into the future and past. This is so because
    the number of objects in its models is much smaller
    than in weather forecast or economy or sociology.
    But the DeltaT seems to be influenced by butterflys,
    flapping their wings in Hong Kong ....

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