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    Re: Land Lunar
    From: Paul Hirose
    Date: 2017 Jan 06, 15:10 -0800

    On 2017-01-05 17:28, John D. Howard wrote:
    > If you set up a telescope ( transit, theolodite ) looking 180 true or 360 if 
    south and lock the azimuth.  With only a hack watch needed you note the 
    merdian passage of a star then the moon, making note of the time difference.  
    Now the time difference is just difference in GHA.
    
    What you have described is the core idea of moon culminations, an old
    method to determine longitudes of fixed points. The largest error came
    from the Moon ephemeris, so transits were also observed from a point of
    known longitude. That cancelled the ephemeris error, and you ended up
    with the longitude difference between the observatories.
    
    Lunar culminations generally had lower accuracy than the mechanical
    solution of transporting sets of chronometers back and forth between the
    observatories.
    
    Chauvenet describes moon culminations and other old longitude methods:
    https://books.google.com/books?id=6JlzJHd15vQC&pg=PA13&focus=viewport
    
    Results of lunar culminations and chronometer transportation to fix the
    longitude difference between America and Greenwich are in the U.S. Coast
    Survey annual reports from the 1850s and 60s.
    

       
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