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    Re: Tycho Brahe Mars oppositions
    From: George Huxtable
    Date: 2004 Dec 4, 00:00 +0000

    Michael Dorl wrote-
    >When George first showed us the Meeus numbers, he said "The times are in
    >TD...."  What is meant by TD?  I know about TDT, ET, UT, and the others
    >stuff in section B of the Astronomical Almanac but TD is not described
    >there.  I guess the times I list above as TDT should really be called ET
    >since they are pre 1984.
    Response from George.
    Precise time has long been in the custody of the French, and I guess that
    TD is short for "Temps Dynamique" or Dynamic Time. It comes in two
    slightly-different flavours, TDT or Terrestrial Dynamic Time, and TDB or
    Barycentric Dynamic Time, depending on whether or not a tiny relativistic
    correction is accounted for. They are so similar that not even Meeus
    bothers to differentiate between them, using simply TD instead. There's no
    practical difference, from our point of view, between Ephemeris Time (ET),
    Atomic Time, and either version of Dynamic Time (TD). Meeus explains, at
    the start of Chapter 10.
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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