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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?

Mike

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