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    Re: facing Mecca
    From: Frank Reed
    Date: 2009 Oct 2, 20:07 -0700

    And which way should you face if you're in orbit around the Earth? This made 
    news a couple of years ago. Here's a little article about it from wired.com:
    http://www.wired.com/science/space/news/2007/09/mecca_in_orbit
    
    Meanwhile, no surprise, there's a wikipedia article about this:
    http://en.wikipedia.org/wiki/Qiblah
    
    It's all there... the issue of rhumb line versus great circle and even which 
    way one should face when praying at the anti-Mecca (yes, they thought of this 
    too... centuries ago). 
    
    There's also a very nice description of a technique for finding the correct 
    direction using some simple positional astronomy: 
    there are "two moments in each year when the sun is directly overhead the 
    Kaaba, the direction of shadows in any sunlit place will point directly away 
    from the Qiblah. This happens on May 27 or May 28 at 9:18 GMT and on July 15 
    or July 16 at 9:27 GMT.
    Likewise there are two moments in each year when the Sun is directly over the 
    antipodes of the Kaaba. This happens on January 12 or January 13 at 21:29 GMT 
    and on November 28 at 21:09 GMT." 
    
    Nice trick. And apparently it was described by muslim scholars at least as early as the 11th century AD.
    
    It is also well-established in Islamic law that the goal is to make an effort 
    to face the right way, not to be exact or obsessive about it. Of course, 
    being exact and obsessive are rituals of the NavList religious persuasion, so 
    for some calculational fun, how much would the above shadow method for 
    finding the direction of Mecca differ from a great circle azimuth or the 
    projection to the horizontal of the "true" line-through-the-earth direction?
    
    -FER
    
    
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