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    Re: The Star of Bethlehem and Navigation
    From: Geoffrey Kolbe
    Date: 2009 Jan 01, 08:29 +0000

    To answer Marcel's question directly, the precision of modern astronomical
    programs to predict the positions of astronomical bodies at any given time
    depends on our knowledge of delta T, which is basically a term to account
    for the slowing of the earth's rotation. Various estimates of delta T have
    been made by various authors. That most respected currently is probably the
    work of F. R. Stephenson and L. V. Morrison, "Long term fluctuations in the
    earth's rotation 700 B.C. to A.D. 1990", Philosophical Transactions of the
    Royal Society, Vol. 351, pp 165-202, (1995). From an assembled collection
    of ancient observations of solar and lunar eclipses, Stephenson and
    Morrison distilled curves of best fits to the data for delta T, with an
    estimate of an error of "not more than 8 minutes". So, modern computer
    programs which can be used to recreate ancient astronomical phenomenon will
    have a formula for delta T built in. However, the timings of astronomical
    phenomenon calculated by these programs for around 2 BC could be off by +/-
    8 minutes.
      Now, +/- 8 minutes of time corresponds to +/- 2 degrees of longitude, so
    this is the sort of error we can put on Koch's estimate of the longitude of
    where Jesus would be born. Rather than pinpointing Bethlehem, it would seem
    the best Koch can do is to say the King of the Jews was born "somewhere in
    Judaea" which would be unsurprising. Kock might say that astronomers in
    those days would have had current observational data and so be able to
    pinpoint the place where the time of the heliacal rising of Venus would
    coincide with its turning from retrograde to direct with greater accuracy.
    I have not read Koch's book, so I do not know if that is his argument. But
    if it is, my response would be a pithy Anglo-Saxon epithet!
    On the matter of lunar occultation, Stephenson and Morrison report that
    there are "many" records of occultations of the planets and stars by the
    moon. "However, owing to the brilliance of the moon, it is difficult for
    the unaided eye to decide whether or not an occultation is actually taking
    place unless the occulted object is extremely bright..." which leads to
    large uncertainty in the timing of such events. From this, I would not hold
    out much hope of a lunar occultation giving the Three Wise Men a pointer to
    a manger in Bethlehem.
    Geoffrey Kolbe
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