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    Re: The Three-body Problem
    From: Peter Monta
    Date: 2021 Oct 25, 22:46 +0000
    Hi Bob,


    Is there any connection here with leap seconds?  I have always understood them to be related to irregular slowing (or, in principle, speeding up) of the rotation of the earth.  Is any portion of the leap second related to actual irregular variations in the orbit of the earth about the sun?


    The second was once defined by the Earth's orbit around the Sun, and indeed the secular change of the tropical year was accounted for in the second's definition under that scheme (there was a term in T^2).  This is already pretty complicated; the tropical year was chosen for some technical reason for which I don't know the particulars.  This definition of the second was shortly replaced by the atomic second, partly because the (empirical?) "acceleration" terms rendered it not very fundamental.

    But, despite all this, I think the brief answer is no, leap seconds are not influenced by any variation of the orbit of the Earth around the Sun.  Leap seconds are purely to keep UTC true to Earth rotation.  If the year were to vary slightly (independently of Earth rotation), that would affect the seasons, yes, but it would not be a driver for adding or subtracting leap seconds under the current system.

    Cheers,
    Peter

       
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