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    Re: Finding longitude in the 12th century
    From: Don Seltzer
    Date: 2012 Aug 31, 11:01 -0700

    The concept seems far fetched at best, when it comes to longitude. First question: what is the prime meridian that the coordinates are based upon? It certainly wasn't Greenwich, or Paris.

    For some scribbled coordinates on a 12th century artifact to be of any use, there must also be the associated gridded map, drawn up by Ptolemy or some other Greek astronomer. There would be little correspondence with modern day reckoning of lat/long, because the astronomers of that period had varying notions of the size of the earth and an appropriate prime meridian.

    A good treasure hunt novel that deals with the problem of shifting geographical references is The Nautical Chart, by Arturo Pérez-Reverte.

    Don Seltzer

    -- On Thu, 8/30/12, Geoffrey Kolbe <geoffreykolbe---com> wrote:

    There is a thread running on the History of Astronomy forum (HASTRO) started by Janie Schwab (schwab---ORG) who relayed a request by a movie script writer. The script concerns an island in the Med where a fantastic treasure is buried. The whereabouts of this island was historically lost, but an artifact with the island's latitude and longitude written on it is discovered in the present day. The heros correct the error in the lat. long. by using a depiction of Orion on the artifact.

    The discussion follows along the lines of finding the position of cities by the timing of lunar eclipses. But one contributer, Clyde Hostetter, says, "I spent some of WWII as a Navy officer, learning and using a system for determining a point's latitude and longitude using only sightings of stars. So did other navigators. The secret was volumes of WPA calculations which were used to convert the star sightings into an accurate-enough location that all Navy ships used...and will again use if the satellites all fail."

    Does anyone here have any comments on this WPA method (whatever that was)?

    Can anyone suggest a means of finding accurate longitude using methods available in the 12th century?

    Is there a way of using a depiction of Orion to correct for an error in longitude?

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