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    Re: Aldebaran occultation
    From: Paul Hirose
    Date: 2017 Mar 7, 11:05 -0800

    On 2017-03-07 9:13, Brad Morris wrote:
    > Alex notes his time of occultation at 3h56m48s.
    >
    > Paul, using up to the minute tools, makes that "4 seconds earlier" at
    > 3h56m44s.
    
    Actually my Lunar4 program was not designed for serious occultation
    computations. For simplicity it assumes the Moon's limb is a perfect
    circle. That's why I gave results to only .01′ precision, and I'm not
    confident about the last digit.
    
    However, I've never tested the program against the IOTA predictions,
    which I assume include all the refinements. At IOTA's nominal
    Indianapolis site the Aldebaran lunar distance errors from Lunar4 are
    +.014′ (begin) and +.012′ (end), but those are only two points on the
    limb. I want to try more points, and more than one occultation to get
    some variation in libration angles.
    
    Don't expect a lunar limb model in Lunar4. I don't think it's worth the
    bother. But the next release may include a small change in Moon radius.
    Currently I use the IAU value, 1737.4 km. Based on private
    correspondence with another enthusiast, I believe 1738.0 km is a better
    fit to the mean limb visible from Earth. That would eliminate about half
    the error in the values above.
    
    

       
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