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Unmanned Spaceflight.com _ Chit Chat _ I have a question about this Cassini Saturn image.

Posted by: Phil Harwell Aug 11 2022, 11:27 PM

Hello, I’m new here. This may not be a productive question, but it’s been nagging me for a while.

After a life of ignorance and doubt, I have re-embraced my love for all things space-related recently. I started by looking at Cassini images. I came across this image, which looks great, but then I remembered that Saturn’s rings are only one kilometer thick. The thought occurred to me: if the rings are that thin, how in the universe are they visible from this far away? I don’t remember the distance, but it’s millions of kilometers away, so I would think they wouldn’t be visible from that distance, unless you’re seeing them at an angle.

I’m sure this is a simple answer, but I’m not knowledgeable enough. Thanks for allowing me to join the forum, and thanks for taking my question.

Posted by: Hungry4info Aug 12 2022, 02:30 AM

It is indeed viewed at an angle. You can see this when the ring goes behind the planet.

Posted by: Phil Harwell Aug 12 2022, 03:44 AM

Oh okay. I totally didn’t see that. Thanks for pointing that out! I can finally rest easy. 😄 It can now go back to being one of my favorite Cassini images.

Posted by: StargazeInWonder Aug 12 2022, 07:14 AM

Additionally, a feature does not have to appear >1 pixel (in this case, in width) to be visible. Stars are visible in, say, HST photos, but are much smaller than 1 pixel, but are very bright. An object that resolves to <1 pixel will still have an effect on the brightness of pixels and so can stand out from the background as a visible feature if the contrast is great enough.

Posted by: JTN Aug 12 2022, 11:32 AM

See also http://satobs.org/tss.html -- a 2.54mm-wide (but rather long) string apparently easily visible from hundreds of km away.
(The angle of which is a couple of orders of magnitude smaller than notionally 1km-wide rings would be seen edge-on at the distance of the above picture, 3.2 million km.)