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    Letcher, "Time by Lunar Lines of Position"
    From: Bob Goethe
    Date: 2019 Nov 12, 15:38 -0800

    I just purchased John S. Letcher's "Self Contained Celestial Navigation with H.O. 208".  In it, he has a chapter, "Time by Lunar Lines of Position".  His initial condition, on page 97, is "It is important for the moon's motion relative to the stars...to be more or less in line with the moon's azimuth, so that a large component of the moon's motion will show up in the moon's altitude."

    I think what I understand by this is that one should make his observation within an hour or two after moonrise, or an hour or two prior to moonset.  However, what Letcher himself says, trying to clarify, is "In this situation, the bisector of the moon's figure in the sky will be within 30 degrees of vertical, the horns pointing up or down rather than being horizontal, and the contact with the horizon will be somewhere near the middle of the illuminuated limb."

    I have up to now thought that the appearance of the moon in the sky varied by the latitude; that what appears to me as a vertical crescent in Canada will appear to an observer at the equator as a boat, or a horizontal crescent.

    It is also true that up to now, I have not given a lot of attention to the moon's aspect at rising, setting, or at its maximum height.

    I know Letcher is doing his best to be clear and concise, but I am confused anyway.  Can anybody help me?

    Thanks,

    Bob

       
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