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*?
2
1
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
2
1
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
1
1
1
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.
1
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.
Sep 21, 2018 · 1:27 AM UTC
1
1


