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Posted by: dilo May 24 2005, 06:02 AM

Between the few visible raw images recently released, lot of interesting rings images... in particular, very unusual pictures like this:
http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=40631
I'm not sure, but I suspect that glare is produced by the backscattered sunlight; in fact, based also on time it was taken and using Solar System simulator, they were made with "zero angle phase" front illumination...
I tried to make a false color (IR+R+G filters) composition; even if images alignment probably isn't perfect, result is amazing :
http://img271.echo.cx/my.php?image=overtherainbow1cb.jpg

Posted by: Bjorn Jonsson May 24 2005, 09:50 AM

Yes, seems to be the opposition highlight. At first I wondered if this might be the unlit side of the rings and whether a bright object (a satellite) might be behind the rings but the viewing geometry makes this impossible and from other images this seems to be the lit side of the rings. Unfortunately there do not seem to be any wide angle images for proper context but a lot more narrow angle images will hopefully soon appear at the JPL site.

BTW the shape and overall appearance of the opposition highlight (assuming this really is the opposition highlight) agrees fairly well with computer simulations I did two years ago :

http://www.mmedia.is/bjj/3dtest/saturn/index.html (scroll towards the bottom of the page)

See also http://www.mmedia.is/~bjj/planet_rend/sat_cass_ohl.jpg

In particular, it seems to be roughly circular, something I wasn't sure of. However, it may be more 'compact' than I expected and brighter where the rings are faint (dark) - it is possible that this is due to an automatic contrast stretch though.

Posted by: dilo May 24 2005, 09:19 PM

Bjorn, your simulations are amazing and very realistic too!
Anyway, now all images are on line and this is a true color combination of another portion (now corrected for hirizontal shift):
http://img189.echo.cx/my.php?image=zeroanglephase6lm.jpg
I suspect subject is the C ring... wath do you think?

Posted by: Bjorn Jonsson May 28 2005, 07:24 PM

Having looked at all of the opposition highlight images I'm now pretty sure the spectacular color in the color composites above isn't real. It is probably due to spacecraft motion, when Cassini moves relative to the rings the opposition highlight moves as seen from the spacecraft. Unfortunately I do not know the times the images were taken and in particular I do not know the time between exposures. However, assuming the time between exposures is similar to the time between exposures for Galileo I should soon be able to get a crude estimate of how much the highlight should move due to spacecraft motion.

Posted by: dilo May 29 2005, 04:29 AM

Having looked at all of the opposition highlight images I'm now pretty sure the spectacular color in the color composites above isn't real. It is probably due to spacecraft motion, when Cassini moves relative to the rings the opposition highlight moves as seen from the spacecraft. Unfortunately I do not know the times the images were taken and in particular I do not know the time between exposures. However, assuming the time between exposures is similar to the time between exposures for Galileo I should soon be able to get a crude estimate of how much the highlight should move due to spacecraft motion.

Posted by: Bjorn Jonsson Jun 4 2005, 01:46 AM

I did an animation showing the viewing geometry when the opposition highlight was visible:

http://www.mmedia.is/bjj/misc/css_stuff/misc/rev008_oppos_highlight.avi (about 3 MB)

The animation 'tracks' the opposition highlight, i.e. the image center is 'at opposition' throughout the animation. This also reveals that the opposition highlight is more 'compact' than in my photometric model of the rings - something I'll need to fix. The field of view is 15 degrees (compared to the Cassini NAC's 0.35 degrees).

Posted by: dilo Jun 27 2005, 10:21 PM

Shine On You Crazy Diamond!
http://img51.echo.cx/my.php?image=shiningringssmall7hs.gif
(click for animation)