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chornedsnorkack
2012-Feb-11, 02:53 PM
What kind of shadow are the Rings of Saturn expected to cast?

It cannot be seen because the satellites of Saturn orbit in the plane of the rings - when Sun is far from the plane of the rings, the satellites pass well clear of the shadow of the rings, when Sun is passing near the plane of the rings, the shadow of the rings is too narrow to be seen.

The total cross-section of the disc of Saturn is something like 80 times the cross-section of the disc of Earth, right?

When the Sun is furthest from the plane of the Rings, roughly how much is the cross-section of sunlight which the rings intercept, compared to the cross-section of the disc of Earth?

Note that planets barely bigger than Earth have been seen transiting (the smaller planets were seen in reflected light, not transit IIRC).

Transit of a planetary disc has a distinctive lightcurve. Rapid fall of luminosity starting as the edge of the disc moves to the star... and then reaching completion in the annular eclipse. All the while no spectral effects (except atmosphere).

Whereas transit by rings would look different - gradual fall of luminosity over some time and only then sudden fall as the planetary disc starts to cast shadow. And then continued gradual fall as the other half of rings starts to eclipse.

How many planets outside Solar System have been seen to have big rings?

Romanus
2012-Feb-11, 03:14 PM
No unambiguous rings have been found, sorry to say.

ngc3314
2012-Feb-11, 03:53 PM
What kind of shadow are the Rings of Saturn expected to cast?

It cannot be seen because the satellites of Saturn orbit in the plane of the rings - when Sun is far from the plane of the rings, the satellites pass well clear of the shadow of the rings, when Sun is passing near the plane of the rings, the shadow of the rings is too narrow to be seen.

Cassini has delivered excellent images of the ring shadows on Saturn. There are also high-resolution radial extinction profiles from stellar occultations (from the Voyagers, Cassini (http://adsabs.harvard.edu/abs/2010AJ....140.1569C), HST (http://adsabs.harvard.edu/abs/1993AJ....106.2544E), and the ground), so a model can be made with essentially arbitrary fidelity to simulate a transit detection.