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