Rings Shadows extended feature

[Calculus]

I don't have an Nvidia video card and therefore I cannot turn on the Ring Shadow option. Does someone know about this problem ?
Let's take Saturn and its rings as seen from earth. When Earth and Sun lie on opposite side of the ring plane, the earth is facing the unilluminated side of the rings. They should be black.
It actually happened in Nov 1995, but I can't simulate it with my Celestia.
Can Celestia render this accurately on an Nvidia card ?

[selden]

Quick answer (I've gotta leave asap): no. Celeestia doesn't render the rings dark. On Aug 6 with the sun above the rings, you can see the shadow on the planet, though. and if you set the time to be about 12 Noon UTC, you can reproduce the upper of the two pictures shown at http://hubblesite.org/newscenter/archive/1996/16/

I'm annoyed that they removed the dates of the photographs from the Web page, but they're still in Goolgle's cache at http://216.239.37.100/search?q=cache:z9rKqUjAIJUC:oposite.stsci.edu/pubinfo/pr/96/16/A.html+saturn+photograph+1995&hl=en&ie=UTF-8

[granthutchison]

They shouldn't really be black, though, since they're composed of particles. Although mutual shadowing will reduce the illumination, some reflected solar light will still be visible (especially in sections of the rings with low optical density, like the C ring), as well as quite a lot of indirect illumination from Saturn. You really just need to go to Saturn and look at the anti-solar side of the rings to get an idea of what Celestia is doing - but I doubt if Celestia is modelling anything like the real situation.

There is, for instance, a reduction in brightness of the rings with phase angle, but this seems to be monotonic - they are completely dark when viewed from the antisolar point. In fact, there should be quite a lot of forward blue scattering from fine particles. Years ago, I modelled this in POVray using two simulated populations of particles:
http://www.solarviews.com/cap/sat/vsaturn1.htm

Grant

[Calculus]

Thanks Guys
These are really nice and interesting images.
It seems really difficult to render the sun light through the rings.

[chris]

I believe that the dark line in the Hubble pictures is not actually the ring system itself, but the shadow that it casts on Saturn. But currently, ring shadows only work on NVIDIA graphics hardware.

--Chris