[Physics] Physics Digest, Vol 7, Issue 3

[cj at mb-soft.com]

Sorry about the Earth/Sun error.  I did all that twenty-five years ago, and my memory is not perfect.

Yes, prior to about 1992, the event had only been witnessed around half a dozen times.  I only learned about that history from a text of Jan Meeus, who is one of the world's foremost experts on mathematical astronomy.  When HE said that no one had ever calculated it to predict a possible observation, I trusted him.  Enough to consume six months of mmy life in endless math.  

As to the results of my calculations, Io and Europa were generally involved, and I was surprised at what a tiny area on Earth could witness such events.  Considering 25 years and my memory, I think that two of the events would only have been visible from somewhere in the ocean, one in African jungle, and one mostly in the Pacific but with a small possible area in southern California.  I had some amateur astronomer friends in southern California at the time, and two intended to take their telescopes out but clouds and storms discouraged them from trying.

It does not surprise me that technollogy has advanced where such "mutual occultations" are now probably regularly predicted.  Your point is well taken that the location  of the Sun and Jupiter's orbit are what is important, and the events can only occur twice every twelve years, when Jupiter passes its nodes.  At the time, I was focused on the exact position of the Earth as many such events occurred during the daytime and over our 75% oceans and such.  It was frustrating to have spent months in doing endless calculations only to discover that no one on Earth could have witnessed them.

My guess is that Meeus was probably involved in enabling the calculations you refer to.

Obviously, I now have another question for you.  Has anyone actually been anywhere that they have witnessed such rare events?  In other words, has anyone photographed or videoed them.  Ditto, once predictions were made, have any of our space telescopes been turned to Jupiter to witness them?

I had actually only brought this up to your group as you are pursuing "one-way measurements of the speed of light", and I had some reservations about the precision of the ideas presented by your group.  It only occurred to me that during my suffering of all that calculation, it had dawned on mme that we have really accurate data regarding the precise locations and positions of the Galilean moons, and timing.  Obviously, if someone witnessed the event on Earth, we could also know that timing to microseconds or better.  And we would know the distance between that location on Earth and each of the two moons involved to a meter or so.  

Even back then, I wondered if that available math might enable a really precise measurement of the speed of light, maybe to even fifteen-digit precision (that would be a million times more precise than the official speed of light, which is defined to nine-digit precision.)

I had just remembered my thousands of sheets of paper, and it now occurred to me that YOU guys might want to try to improve the value of the speed of light.  If you could do it, the scientific community would applaud you.

No, the "error" you accuse me of is actually yours.  The geometry is very strict.  Like the fact that next month, much of the Earth will be able to witness a solar eclipse, in nearly all locations, it will be partial eclipses.  Only in specific locations like near Saint Louis, MO, will it be total, in that case for up to about two minutes.

What you are guessingn at is that much of the Earth would possibly witness a PARTIAL mutual eclipse regarding the Galileans.  My interest, then and now, was only for TOTAL eclipses.  My calculations also predicted one annular mutual eclipse (due to the different diameters of the moons).  

I look forward to you informing me about the informsation you have found.

The nodes of Jupiter enable several months of possible mutual eclipses every six years.  Nearly all of those are partial eclipses.  Only very few events could be witnessed from very limited locations on Earth, if a total eclipses was wanted.  There are also two categories of such events.  Most of them occur while the moons were passing over the bright surface of Jupiter, where the shadows of each moon are visible on the face of Jupiter.  A mutual eclipse is hard to detect.  The far rarer events occur when the moons are NOT passing over Jupiter's face.  I think that Meeus said that the first such event ever seen was around 1880, and the astronomer was very confused.  The next was about thirty years later.  Very rare, especially when no one had ever tried to predict the events.  

Carl Johnson
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