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    Re: A Jupiter Puzzle
    From: Frank Reed
    Date: 2011 Oct 14, 07:06 -0700

    Marcel, you wrote:

    "just an additional detail. Your estimation of the time zone happened to agree with the adopted one at his location but not quite relative to the longitude range which extends for UT+1h from 7.5E to 22.5E. His 7E correspond to UT, or rather to betweeen UT and UT+1. This is still surprisingly close for your rough estimation."

    You do understand that the only information that can be determined astronomically from the images is UT (GMT), right? Information on the time zone follows from the time stamp on the images. Based on the angular rates of Europa and especially Io when not near the extremities of their orbits (where the apparent angular rates become close to zero), the time with this magnification and resolution can be determined from the positions of Jupiter's moons to within a couple of minutes.

    By the way, a proper exposure of the Moon and nearby bright stars would yield UT more accurate by roughly a factor of ten. With the Moon, you may have to find a way to reduce its brightness relative to background stars and you need to take corresponding star-star photos to calibrate the angular measure. Greg has tried some of these with his digital SLR camera. High tech, right? Maybe not. The first photographic lunars using these techniques were apparently taken by Henry Schlichter in 1891-1892. That was too little, too late, even for land exploration and surveying (the last refuge of lunarians), but the method apparently worked well. I believe this is the original article on Schlichter's work:
    (from the Royal Geographic Society, 1892).


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