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    Re: venus
    From: Michael Dorl
    Date: 2004 Oct 13, 10:48 -0500
    At 03:00 AM 10/13/04 -0400, you wrote:
    George H wrote:
    "I get 16d 05.1'; Frank
    calculates 16d 05.5'. So there's a discrepancy of 0.4' between us,
    somewhere, in the process of allowing for semidiameter(s) and clearing the
    lunar distance. Not an enormous divergence, and certainly much smaller than
    the difference Michael Dorl observes with his measured distances. But
    clearing the distance and allowing for semidiameter should be a rather
    exact science, so I wonder why we disagree by that amount. It might be
    enlightening to track it down."

    Thanks for questioning this. It could easily be that I've got a sign wrong somewhere or something like that. I'll see what I can find. And thanks also to Fred H, Herbert P, and Michael D for posting their calculations which all seem to differ from mine. By the way, does anyone do oblateness the way Chauvenet does? That's how my calculator does it.

    Here are the bloody details on the calculation of TPC for Geocentric coordinates from Mosier's
    routines for Venus and the Moon

    dt = 64.4 seconds
    temp = 5C
    pressure 1010 MB
      elevation 294M
                                      Venus                          Moon
    geocentric RA             10h34m45.1022s          9h37m13.8949s
    diurnal aberration         0.0076s                       0.0113s
    dirunal parallax            0.3498s                       2m7.3158s
    refraction                    -5.6126s                       -3.2805s
    tpc RA                       10h34m39.8470s           9h39m17.9415s

    geocentric DECL          9d40'04.3470'"             19d29'00.7421"
    diurnal aberration          -0.0346"                      -0.0573"
    diurnal parallax             -4.8748"                     -26'23.5639"
    refraction                     1'18.7829s                  41.3482"
    tpc DECL                    9d41'18.2205"              19d3'18.4692"

    I an supply the details on the J2000 to Geocentric transformation if that would help but
    I think we all three agreed on the Geocentric position.

    Calculating Venus/Moon Ctr/Ctr distance from TPC coordinates, one gets  16d20'22.16". 
    Assuming Moon semi-diameter of 15'3.876" gives distance from venus to Moon limb of
    16d05'18.284" = 16d05.3"; half way between your two estimates.

    As far as I can tell there is nothing in the routines to allow for oblateness of the earth. 
    One can specify a elevation. Looks like the earth is assumed to have a radius of 6378137
    Meters, same as my 1988 AA page K6.

    I remember someone saying "It's a good thing there are so many standards, you get to choose
    one you like." :-)

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