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    Re: Jupiters moons and time/longitude
    From: Francis Upchurch
    Date: 2014 Jun 8, 09:31 -0700

    Hi stan,

    Thanks.

    Yes, Chinese 4 inch, (120mm) refractor cost about $ 150-200 a few years ago, so I guess, maybe not cheap, but not hugely expensive? Don't know what they are now. Anyway, good enough and probably a lot better than Galileo's original, so what a man he was! I just found it very difficult to accurately time the immersion/emmersion. Wondered if anyone else has done it succesfully? My lunars are more accurate (within a minute or 2 (time),(and can be done at sea)  than my Jupiter moons(within 2-5  mins) (land locked), but I will try my new 5 inch reflector maybe in a couple of months, health depending! 

    My "game" is basically an "Endeavour" type navigation style using a reasonalble mechanical watch (or no watch), lunars, but I cheat by using LOP fixes sun/moon which they did not do. I also cheat by using the Fuller+/- Bygrave slide rule because I'm bored with log tables, but enjoy slide rules as  I enjoy sextants. No electronics involved, except I cheat again by printing out a "pre-1912 Almanac" with 3 hourly predicted LDs from Frank's wonderful site. But Cook had the first  1767? Nautical Almanac with these on Endeavour,. (but not for the last 18months of the voyage ,when he had to rely on the long 4 hour Mariners Guide method.)  lunar clearance takes me 5-7 minutes with the Bygrave and 7-10 minutes with the new mini Fuller, which is a lot faster then the original Fuller)

    Any advice on Jupiter moons would be appreciated.

    Francis

       
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