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Modris,

Yes! You're on it. That's exactly how I looked at it. The zenith would be nice to have. Given the known UT on a given date (which, btw, I added to the puzzle to guarantee its 'solvability') then the R.A. (or SHA) of the zenith gives the longitude, and of course the Dec of the zenith is the latitude. But, as you note, we can't really properly find the zenith because the images are somewhat distorted. But, aha!, the horizon provides a surrogate: the declinations at the N/S points are equivalent to the declination of the zenith, after a little arithmetic, and, equally important, the RA/SHA values at the E/W points on the horizon should average to the same at the zenith.

Another hint that may be interesting: look along the ecliptic/zodiac. There's something surprising added in. Why? And why only "that one"? Is it related to the location of this signage? I'm not saying I know for sure on this... It's interesting!

Frank Reed

Here are the original images of the star charts in question, for anyone who missed them on the first pass:

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