Hi Bernd,

> on a german planetary mailing list an animation was shown that looked
> like a shadow of a saturnian moon on the ring.

I'd wondered if something like that might be visible. (In the real
world, I mean. Unfortunately, Guide doesn't show the shadows cast
by satellites on the ring, nor shadows cast by the ring on satellites.
All it shows are shadows cast by Saturn on the rings and the satellites,
by the rings on Saturn, and by the satellites on Saturn.)

I've thought about adding ring/satellite shadows. One problem is
that because the satellites are almost coplanar to Saturn (*), you'd
only see them when the rings are edge-on to the sun. At which point
the rings almost vanish anyway.

> PS: The time of imaging was 29.03.2011 23:48 UT.

I tried setting Guide's date/time to this, and the viewpoint to the
Sun, just in case I might see a satellite in front of the rings. As
I expected, we're too far from the Saturnian equinoxes to see something
like this. Mimas, Pan, and Enceladus are in front of Saturn, and
are presumably casting shadows onto the disk of Saturn; but they wouldn't
cast anything onto the rings.

-- Bill

(*) Except for Japetus/Iapetus. Once or twice every fifteen years,
this satellite is placed to cast shadows onto the ring, or vice versa.
On 1889 Nov 2, E. E. Barnard observed such an eclipse from Lick Observatory.
If you animate that event as seen from the Sun, you can see that Japetus
went behind the rings. I think that the fact that Barnard saw that Japetus
didn't disappear was what clinched the idea that the rings weren't solid.

However, when Japetus casts a shadow on the rings, that very definitely
_should_ be visible. I doubt the shadows of any other satellites could be
seen.