[X] My Assistant

[Bjorn Jonsson]

The following 'image' is based on intensity scans of the unlit side of the rings:



The upper profile was measured from Cassini images and the lower profile from Voyager 1 images.

This is an improved and updated version of the image I posted in this thread almost two months ago. Now the profiles should match almost perfectly (the maximum mismatch shouldn't be more than 1-2 pixels).

The relative intensities within each profile should be approximately correct (especially in the Cassini profile) but I made no attempt to make the intensity of the Voyager 1 profile correct relative to the Cassini profile.

Nevertheless it is obvious that there are large differences. The Cassini division is by far the brightest feature in the Voyager 1 profile, followed by the C ring. In the Cassini profile the F ring is brightest, followed by the outer A ring. Also in the Cassini profile the Cassini division is much darker relative to the B ring than in the Voyager 1 profile. Remarkably the inner part of the B ring is brighter than the C ring in the Cassini profile. The higher quality of the Cassini imagery is evident but these differences are nevertheless real.

I assume the reason for these differences must be different phase angle: The Cassini images where obtained at a phase angle of ~130° while the phase angle in the Voyager 1 images was much lower. A much higher solar elevation angle in the Cassini images might also contribute a bit.

Anyway it is clear that the photometric behavior of the rings as a function of phase angle, solar elevation and the viewing geometry in general is complex and nonuniform across the rings.