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    Re: The Star of Bethlehem and Navigation
    From: Michael Dorl
    Date: 2009 Jan 03, 20:42 -0600

    frankreed@HistoricalAtlas.com wrote:
    > By the way, the introductory web page shows an example of an ancient 
    astronomical observation (the most ancient?) that puts a strong constraint on 
    delta-T: the solar eclipse of March 5, 1223 BC seen at Ugarit in Syria. If we 
    have records stating that an eclipse was seen from a specific place, all we 
    need to do is change delta-T by trial and error until the eclipse path 
    crosses the observer's location. The catch in this case is that the tablets 
    recording the eclipse aren't dated. So you need some other information to 
    narrow the date to the nearest century or two.
    > -FER
    I start up my almanac program and put in the lat/log of Ugarit (35.8E 
    35.683N), set the date to 3/5/1223 BC and play with the time until I get 
    the lunar distance of the sun as low as possible at 1152.  I then have a 
    separation of 4' 9.3".  I diddle delta T which my program has set to 
    28404.763 and find I can get a closer approach at 11:50 with a delta T 
    of 28460.000.
    So what am doing when I diddle delta T?
    The picture I have in my mind is a sphere with the path of the eclipse 
    outlined on it with an overlay sphere with a map of the world on it.  So 
    by changing delta T I  revolve the map about the earths axis  relative 
    to first sphere to bring Ugarit closer to the center of  the path of the 
    eclipse.   So delta T is constrained to those values which bring Ugarit 
    into the path of the eclipse.
    Is that an ok way to think about it? 
    Hopefully my almanac has also made some reasonable adjustments for 
    changes in the earths axis.  Are those know well enough and predictable 
    enough to project them 3000 years into the past?
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