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    Re: additional planet corrections...
    From: Bill Murdoch
    Date: 1999 Nov 23, 7:13 PM

    As Chuck said the additional correction for Mars and Venus is for parallax.
    It is needed because those planets can be close to the earth and the observer
    may not on a line between the center of the earth and the planet.  You can
    find that in section 13 of the Explanation in the back of the almanac.
    "...but additional corrections for parallax (page A2) are required for Venus
    and Mars."
    Be aware that from 1952 to 1984 the additional corrections for Venus allowed
    for parallax and for phase.  The phase correction was required because the
    tabulated position for Venus was for the planet's center of disk.  From 1985
    onwards the tabulated position of Venus was for its center of light.  Old
    text books (and some newer ones) still discuss the phase correction, but is
    no longer needed.  See B.D. Yallop, NAO Technical Note Number 55, The Phase
    Correction of Venus.
    Bill Murdoch
    Bill Murdoch

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