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    Re: Moon Occultation of Jupiter
    From: Frank Reed CT
    Date: 2004 Dec 1, 01:21 EST
    David Edwards wrote:
    "Apparently there will be an occultation of Jupiter by the Moon on Tuesday 12-07-2004 at approximately 0355 EDT.  It will end at approximately 0505.  I would assume that for a celestial navigator an accurate determination of local time, or even better an LOP, could be computed from a knowledge of when the beginning and/or ending of this event will occur in universal time.  Would that not be a very elementary lunar calculation?  Look at the moon with binoculars and set a chronometer to the correct universal time at the exact moment that Jupiter disappears behind it."
    Yes (except for the bit about "elementary calculation"). This wasn't often done historically (by navigators at sea) because the calculation is rather long and tedious, and occultations are relatively rare. But it works in principle. To get an idea of the difficulties, take a look at the maps of the occultation times on Sky & Telescope's web site here:
    Notice that the "line of position" you would get is an oddly shaped arc --clearly not an easy thing to calculate. But if you have these maps (and note that it would have been possible to publish them in the almanacs even 200 years ago if there had been sufficient practical value), and you see Jupiter disappear at, say, 0855 UT then you must be somewhere along that curve that crosses southern Canada, runs down the US east coast and then swings over to northern Texas. You can turn it around, too, and use this event as a chronometer, but again the calculation is long. Timing the event is not all that difficult (contrary to some other comments on the list) but it does require binoculars or a small telescope. 10X magnification would probably be optimal.
    It should be a beautiful sight and well worth waking up for it!
    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
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