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    Re: Archeological Celestial Question
    From: Paul Hirose
    Date: 2018 Jan 18, 14:44 -0800

    On 2018-01-17 12:23, Mark Coady wrote:
    > The case is that many antiquity structures are positoned to precise 
    solar/lunar/star correlations.  Favorites include stonehenge roughly 2950 BC? 
    and others aligned to summer and winter solstice events.
    >   Is there a handyonline calculator that goes that far back?  So I could 
    look at a true satellite shot with bearings vs actual angular position on 
    that date in 2950 BC? Are there any accumulated earthquake/shock events on 
    earth that might make any uniform calculator erronoeous by any signifcant 
    amount?
    
    I forget how far back JPL Horizons goes, but surely it can reach the era
    of Stonehenge. It uses a special long term precession model for dates
    before 1800 (I think) and the latest JPL long ephemeris, the DE431.
    
    There's considerable uncertainty about delta T in the remote past, and
    that's an issue for some ancient events. But it doesn't matter for
    alignments, which deal with rise and set azimuths, and perhaps altitude
    at culmination. These are a function of the direction of the pole but
    not Earth's rotation about the pole.
    
    Earthquakes don't seem to have any significant effect on Earth
    orientation. Even after a major one, I see no bulletins from the IERS
    regarding a jump in the polar motion and offset of the pole.
    
    You'll probably get a more informed answer at the HASTRO-L (History of
    Astronomy) discussion group.
    

       
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