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    Re: Ulugh Beg's sextant
    From: Frank Reed CT
    Date: 2006 Mar 26, 18:05 EST

    Herbert, you wrote:
    "E. B. Knobel  investigated the accuracy of Ulugh Beg's star catalogue in
    the introduction  to his edition of it. After grouping the stars into
    northern, zodiacal and  southern ones, he shows a systematic bias in
    longitude of 18', 14' and 4'  respectively. Then he subdivides each group
    into 18 sub-groups, each 20 deg  of longitude wide. The corresponding
    errors in longitude fluctuate about a  quarter of a degree around those
    means, occasionally a little more.  Therefore, some longitudes are more
    than half a degree off the truth.   The errors in latitude are of a
    similar magnitude. From what I see, they may  be just marginally better
    than those of Ptolemy/Hipparchus."
    Very  interesting. Thanks. It strikes me that the accuracy in latitude should
    be  better than that in longitude. No?
    What is the origin of this myth that  the positions were accurate to a few
    seconds of arc? A number of web sites quote  an article by "Kevin Krisciunas" on
    this point. Maybe it's just that single  source.
    42.0N 87.7W, or 41.4N  72.1W.

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