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    Re: venus
    From: Frank Reed CT
    Date: 2004 Oct 9, 18:01 EDT
    Alex E wrote:
    "I remember Frank Reed said something about "not using Venus" in Lunar distances, recently, but I don't remember what was this exactly, maybe the non-zero size of its own disc."

    When shooting lunars using planet, it was customary to place the center of the planet's disk on the Moon's limb. This is easy to do with Jupiter, and even helps to make these observations more accurate (than lunars with stars, that is). Venus, and to a much lesser extent Mars, has an appreciable phase, ranging from a large, thin crescent to a very small round disk. A navigational enthusiast with a lot of time to spare and considerable knowledge of observational astronomy could probably correct for this today, but it's no trivial matter.

    In practice, in the first half of the 19th century, the great majority of lunars (at least aboard American commercial vessels) were apparently Sun-Moon lunars. Stars were sometimes used; the planets almost never.

    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
       
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