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    Re: Tycho Brahe Mars oppositions
    From: Michael Dorl
    Date: 2004 Dec 3, 12:33 -0600

    I had a chance to look at the code in the Mosier routines and I'm virtually
    certain the ecliptic longitude is the true heliocentric ecliptic
    longitude.  So, I get a time of 11:44:00 TDT dT= 95.4 for the 11/18/1580
    opposition TDT JDate 2298474.98889.  George's earlier message gave a time
    of 11:41 TD.
    At the time of the opposition, the difference in the ecliptic longitudes is
    changing at a rate of about 1.25 arc seconds for each minute of time.  I
    take this to mean that my calculated ecliptic longitude difference varies
    from that calculated by Meeus by no more than 4 arc seconds.
    In investigating this, I added some code to produce the heliocentric
    ecliptic position of the Earth.  I suppose it's obvious to the rest of you
    but it didn't occur to me until I saw the numbers that the Earth's true
    heliocentric ecliptic longitude differs from that of the true geocentric
    ecliptic longitude of the Sun by 180 degrees.
    I was also surprised that the Earth's heliocentric latitude was essentially
    zero for the entire orbit.  After all, the ecliptic is the mean plane of
    the Earth's orbit around the Sun.
    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.
    Sorry to continue to beat a dead horse but I tend to learn best from these
    pathological cases.

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