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    Re: Astrolabe. was: [NAV-L] The point of it all
    From: George Huxtable
    Date: 2006 Jun 29, 10:49 +0100

    Lu Abel wrote-
    
    
    | Does anyone know of a simple explanation of how to use an astrolabe?
    | I've always been fascinated by the devices but have no idea how they
    | work or how a Muslim pilgrim might have used one to find Mecca's
    | azimuth.
    
    There isn't really a SIMPLE explanation, in that it is such a subtle
    device, with so many possible uses, that any explnation has to be
    somewhat complex.
    
    This may not help much, I'm afraid, but many years ago I bought a
    plastic astrolabe about 6 inches diameter, quite cheaply. This has all
    the features of the brass instrument, and was more usable and precise
    than many of those, with stars printed on a transparent plastic disc
    (unavailable to the ancients). It came in a wallet with a little
    booklet "The Astrolabe" by its designer, Harold N Saunders, who was
    then (1971) at St Merryn, Stratton Road, Bude Cornwall EX23 8AG.  That
    was quite a long time ago now, and it seems that his astrolabe is no
    longer sold at the Museum of History of Science in Oxford, who are
    astrolabe specialists. They may be able to suggest alternatives, at
    +44 1865 277280 (afternoons only, UK time). A Saunders astrolabe may
    occasionally surface on Ebay (most likely the UK version of Ebay).
    Other printed astrolabes are being made, I understand, some very
    expensively.
    
    To understand the subtle functioning of an astrolabe, while you read
    about it, it helps considerably if you have some version of the real
    thing to hold in your hands and twiddle. A nice alternative to that
    plastic astrolabe is a web version, which can be nudged about on the
    screen, by pressing buttons. This is "Keith's automated astrolabe",
    which you can get to via Keith's home page at
    http://www.autodidacts.f2s.com/index.html  . Keith lives in England,
    not far from where I do.
    
    In some ways Keith's astrolabe is actually better than the real thing
    (though I have a reservation or two about some of the fine detail).
    It's great fun to play with, and very informative. Give it a try.
    
    ===================
    
    As for Lu's question about "finding Mecca's azimuth", I think that's a
    job that an astrolabe is unable to do; or at least, I don't know how
    that could be deduced knowing your lat and long, and Mecca's. You
    would need a globe, or an armillary sphere; something like that. What
    an astrolabe can do, if you know Mecca's azimuth, is to help to point
    you in that direction from observation of Sun or star. The other
    important function, for a Muslim, is to tell him the proper time for
    his prayers, by observing Sun or star altitudes.
    
    George
    
    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
    

       
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