http://media.zenfs.com/en_us/News/Reuters/2012-12-19T035245Z_616564795_TM3E8... SATURN.JPG Whoa, zoom at the right edge of the shadow and you can see variations in ring thickness! Now, a nice puzzle... On Sun, Dec 30, 2012 at 6:47 AM, Bill Gosper <billgosper@gmail.com> wrote:
See last link for comparison views.
Fred>
RWG's incomprehension is way ahead of mine --- I cannot make visual sense of this abstractly impressive graphic at all! WFL
rwg> Confession: I had Neil explain it to me first. But now I really get it. It's majestic! The northern hemisphere, lit by the bright upper surface of the rings, soars above them.
The central dark smudge is due to the planet's shadow on the rings. The southern hemisphere is faintly lit by the light we see filtering through the underside of the rings.
The equator itself is dark because the rings edge-on are almost invisible.
[...]all we need is scatter and density. A backlit ring can be faint if too tenuous, or too dense to transmit. There's a density of maximum brightness. The apparent density varies with viewing angle.
Note how the rings brighten with distance. Backscatter varies even more strongly. Look how the relatively tenuous inner rings light up the area just above the equator.
... rings brightening with distance only makes sense for the tenuous ones. Viewing rings at a shallower angle makes them look denser. Why the bleep does the broad, dark, central ring brighten with distance in the main pic (where it gets green) and in backlit.png? It's obviously dense--notice its opacity in both views in backlit.png . Spoiler below.
MRob> I think it's the E ring, but maybe it's the G ring. See:
http://en.wikipedia.org/wiki/File:Saturn_outer_rings_labeled.jpg
Ah, I'd somehow forgotten about those distant, fuzzy ones <http://gosper.org/backlit.png>. --rwg
Consider neutrinium: a gravitationally closed ball of neutrinos.
Spoiler: the "green" from that ring is not transmitted. It's the "underside" (unsunlit side) lit by the sunlit southern hemisphere! So there are *two* mechanisms brightening the distant reaches of the translucent rings. Note how this complicates the variegation of that atmospheric arc near 4 o'clock on the limb. --rwg