Perspective/geometry/celestial mechanics question that's baffled me for years. I took this photo tonight ~1 hour after the sun set. Camera perfectly level. Why, if the sun has set toward the right of the frame, is the moon shadow's axis of symmetry still inclined *upward*?
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I think: 1. If the moon were precisely on the horizon (0° elevation), this wouldn't happen. 2. If the moon were straight above (90° elevation), you'd see this if the sun had set >90° right of where you'd aligned (and then elevated 90°) your camera, but not if <90° right 1/2
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3. When the moon is at some intermediate elevation (between 0° and 90°) then the threshold for this effect would increase from >90° to the right (at 90° elevation) to higher angles as the moon gets lower. Maybe it doesn't hit 180° right until 0° elevation? Not sure yet. 2/2
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Replying to @davidbaron @stshank
Also, per timeanddate.com/sun/usa/san-… sunset yesterday in SF was at 272° and per timeanddate.com/moon/usa/san… moonrise was at 115°. So the sunset was 157° to the right of moonrise, though that angle difference would be smaller 3 hours after moonrise, but probably not by a huge amount.

Sep 20, 2018 · 11:56 PM UTC

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Replying to @davidbaron
157°? That's awfully close to 180° and I thought sunset and sunset was 7:09 p.m. to my photo at 7:18 p.m. I'm no expert here, though.
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futureboy.us/fsp/moon.fsp has good data for this. 24° elevation, bearing of 146° (so 126° right of the sunset), and a picture the shape of yours... assuming San Francisco location.
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