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    Re: Jupiter-Moon Lunar from a photo
    From: Frank Reed
    Date: 2020 Dec 24, 07:46 -0800

    Modris, you wrote:
    "I did not even start to analyse whether such a combination of Saturn, Jupiter and the Moon (in such a phase) in the same position against the stars is possible in other year and date, because it seemed obvious that it could happen maybe once in hundreds or even thousands years. I have no idea preciselly the probability of such a coincidence :)."

    Even setting aside the condition that these are Jupiter and Saturn... If someone handed you this image and said "it's generated in software... what date, time, and location does it represent?" you could probably narrow down to the parameters we have discussed. Various combinations of Venus, Mars, Jupiter, and Saturn might make similar conjunctions, but to find them exactly as displayed among those fainter stars with the Moon in that same position... it's certainly a once in centuries event, as you have said, and I agree, it may even be once in a few thousand years, within the limits of positional accuracy of the image.

    In science fiction time-travel, my "inner geek" sometimes wants to yell at the video (or paper-based equivalent) when the travellers can't figure out "when" they are in time. For example, from a movie released in 1986 with a pair of whales in it, our formerly-dead hero announces after a quick time-travel hop: "Judging by the pollution content in the atmosphere, I believe we have arrived at the latter half of the 20th century." Grrr... I get it, of course. It's a little wry humor about air pollution, which was still a top drawer concern for US movie audiences back then. But nothing about the positions of the planets?! Don't they know what we know?! Even "mere astrologers" would know this one (in fact, probably better than most professional astrophysicists). The positions of the planets determine the date and time with great accuracy. We don't need to sample the atmosphere or listen to the headlines on the radio to figure it out! At least for dates within a hundred thousand years of the present, the sky is a reliable calendar and a reliable clock within a thousand years.

    Back to the photo that started this, if you're game, Modris, I'm still interested in the issue of the sensitivity of the navigational "fix" in this analysis. Throwing away the lighthouse and other non-astronomical clues, what is the possible range of positions, dates, and times that would work for this photo given reasonable limitations on our ability to determine celestial coordinates from the photo? And in this case, yes, we can limit ourselves to December 2020. :) 

    Frank Reed
    Clockwork Mapping / ReedNavigation.com
    Conanicut Island USA

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