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    Re: Mars - Mercury Question
    From: Alexandre Eremenko
    Date: 2013 Feb 3, 00:47 -0500

    It is not possible to determine longitude from the distance
    between Mars and Mercury with an ordinary sextant with
    reasonable accuracy.
    Here is a very crude estimate.
    Mercury has period about 88 days.
    And the maximum elongation from the Sun is about 20 degrees in the
    average. Which means that Mercury moves less than 1/4 degree per day.
    While the Moon moves roughly 12 degrees per day.
    Thus determination of the longitude from the Mercury distance
    to anything will be
    about 50 times less accurate than from the Moon distance.
    Definitely out of the limit of the Longitude prize:-)
    I am not even mentioning the difficulty if seeing Mercury
    through the sextant telescope.
    On Sat, 2 Feb 2013, Brad Morris wrote:
    > Coming up this week, Mars and Mercury will be in close angular proximity to 
    each other.  Mercury, of course, is one of the swiftest moving planets in the 
    solar system.   Both Mercury and Mars are in the ecliptic plane.
    > The question is basic.  Can we tell our longitude by the angular separation 
    of the two bodies, similar to a lunar?  Can we do this with a sextant?  We 
    might be able to tell our longitude using this method, but its below the 
    measurement sensitivity of a sextant.
    > Just asking!
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