MarkBour wrote: ↑Wed Feb 16, 2022 5:52 pm
neufer wrote: ↑Tue Feb 15, 2022 10:40 pm
johnnydeep wrote: ↑Tue Feb 15, 2022 9:39 pm
Yeah. Now why exactly is that? At least one crater still does have very prominent rays, so why don't all of them?
And another stark difference is the absence of edge bumpiness on this "terminator moon". Again, why?
I'm not sure why neufer brings up the Seeliger effect here. Today's APOD is composited slices of images, each taken when the sun is off to the side of each section. Art, are you saying that rays are most visible with straight oppositional lighting? Or do they show up best somewhere in between side lighting and oppositional lighting?
As to the lack of bumpiness on the edge, I haven't really seen it in other images to compare. johnnydeep, you must have better examples than I have. I've only noticed it in eclipse images that dealt with Baily's beads. I do see a little bumpiness only at the top of this image. Perhaps the smooth edges were part of the process in which the composite was put together, or again, perhaps the visibility of such features are reduced by the angle of the lighting.
I think neufer is implying that the rays are very bright features that best show themselves when the Siegler effect applies, like when the moon is full. And the absense of the bright rays is expected in the darker, shadow-rife environment of the terminators. But that still wouldn't explain the presence of some rays, unless those happen to be very rough and bumpy compared to most rays.
As for bumpy moon edge, the full moon picture I used above shows it, but the full res version shows it better. That's here - high_resolution_photograph_of_the_full_moon. Here's a close-up of part of the bottom edge:
bumpy limb of full moon.JPG
In contrast, this APOD shows a perfectly smooth edge all the way around. Here's a part of the bottom edge:
smooth edge of terminator moon.JPG
Perhaps it's just an image processing artifact?
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