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    Re: Longitude by altitudes. was Re: How Many Chronometers?
    From: Marcel Tschudin
    Date: 2009 May 13, 01:42 +0300

    Thank you Frank for indicating those alternative possibilities. I
    enjoyed your proposed Roman navy.
    Your reflections triggered actually the following thoughts:
    Assuming that "they" (or your Romans) new:
    - how to calculate for a given day the position of the moon relative
    to the sun for e.g. the moment of sunset at their reference location
    (Rome, Babylon, Greenwich or whatever).
    - how to measure latitude
    - how different latitudes shift the moment of sunrise/sunset
    - measuring shorter time intervals e.g. with a water-glass
    It seems to me that with those preconditions it should have been
    possible to obtain at e.g. sunset the time difference between the moon
    positions of their reference location and the observed one and from
    this the difference in longitude. Or, do I oversee here something? I
    haven't analysed the error propagation and do therefore not know the
    accuracy to expect from proceeding this way, but the moment of sunset
    should about be as accurate as the determination of the latitude.
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