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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Moon Occultation of Jupiter
From: Frank Reed CT
Date: 2004 Dec 1, 01:21 EST
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
[ ] Mystic, Connecticut
[X] Chicago, Illinois