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    Re: watch as compass
    From: Bill B
    Date: 2007 Jul 29, 00:06 -0400

    >> Frank Reed  wrote
    >> Finally, the Sun can indeed be used as an accurate compass if you know
    >> the local time, but you need to know a little basic astronomy to get
    >> it right. I won't go into details on this. I just wanted to point out
    >> that the watch trick can go very badly wrong in some latitudes at some
    >> times of the year. It's "better than nothing" but not much.
    >
    Jim Van Zandt responded:
    
    > You don't even need the local time - just a stick and a piece of level
    > ground.  Poke a stick in the ground and mark where the end of its
    > shadow falls.  Wait.  The shadow will move directly east.
    >
    > Of course, checking your directions this way very often will slow your
    > progress.
    
    I sense a stick in the ground is setting the sun dial back thousands of
    years.  If in the northern hemisphere and you angle the stick to point at
    Polaris you might stand a fighting chance.
    
    Past that, I am clearly missing something here.  The shadow will eventually
    move directly east, assuming the Sun's declination is above zero in the
    northern hemisphere.  The question is when related to a watch?
    
    By my reckoning if you know local time (say noon compared to watch time) you
    can then roughly derive LHA at another time at the same longitude.  With
    that, PLUS declination and latitude, you can derive the Sun's elevation.
    With elevation and the above information you can derive the azimuth.  Or use
    some of the nifty formulas presented on the list in the past to move
    directly to azimuth.
    
    Perhaps a better strategy would be to measure the stick's shadow to
    determine local noon (Sun south or north as the case may be), then construct
    a 3-4-5 triangle to determine east or west.
    
    I would personally go with moss on trees. 
    
    As Frank (if memory serves) initially pointed out, LHA has a very loose
    correlation with azimuth (except at local noon).  I have been playing with
    determining longitude by measuring the Sun's elevation when at 270d azimuth
    (to heck with east--I'm a late riser).  At 40N the time of 270d is nominally
    changing 2 minutes a day now.
    
    Bill
    
    
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