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    Re: Jupiter-Moon Lunar from a photo
    From: Frank Reed
    Date: 2020 Dec 20, 13:46 -0800

    Modris, you wrote:
    "I measured the lunar distance between the Moon and the star 52Sgr. I took star coordinats from Stellarium. Then I cleared lunar distance and got time: 17:12:00 UTC. Then I calculated latitude by two stars (52Sgr and 59Sgr). The latitude came out 39° 21N. And from this latitude and star altitude I calculated longitude: 5° 57E. The result is in the middle between Sardegna and Illes Belears. This result is closer to Mangiabarche lighthouse than my previous one."

    Excellent! And, yes, that's very similar to how I analyzed it. The only real difference is that I did it "by eyeball" in Stellarium rather than performing any actual calculations. Your calculations are clearly more precise, but we ended up in the same place. :) The key here, which makes this photographic "lunar" different from some others we have experimented with, is that there are numerous faint stars visible in the photo. I highlighted a bunch in my original post hoping that this would be a useful hint. The presence of stars close to the Moon largely eliminates the "plate constants" problem (the projection of the sky onto the plane of the photo). The purpose of measuring lunars with a sextant is to locate the Moon's position in the sky, but if we have lots of stars close by, then we can directly read off the coordinates of the Moon's center from a local coordinate grid defined by those faint stars.

    Another potentially useful trick that you can try in Stellarium: if you tap the comma ( , ) key, Stellarium displays the ecliptic. One can then draw in the ecliptic line in the original photo by checking to see where it passes near certain faint stars and based on its distance from Jupiter-Saturn. Then it's possible to measure the tilt of the ecliptic relative to the horizon and compare against the same tilt in Stellarium. Greg (if you're reading along), this is how we would be able to tell that your estimate up near Denmark and southern Sweden wouldn't work. At that higher latitude, the inclination of the ecliptic would be too shallow. The longitude is close though, for a photo, and that was the main thing!

    In my original post I offered two non-astronomical hints. I said "that lighthouse eats boats and the photographer has gone viral..." The first part is just the translation of "mangia barche". That's Italian for "eats boats" (at least by a simple translation). It sounds a little ominous and contradictory for a lighthouse, but it's the name of the reefs and rocks there. As for the photographer, his name is Giovanni Corona, and I suppose he's been dealing with gallows humor over his name "going viral" for nearly a year now...

    Google Maps link for Faro Mangiabarche

    Frank Reed

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