Ring near edge on illumination, Ring particles are casting shadows Options

[Astro0]

nprev...not sure what time period. Someone here will be able to tell us I'm sure.

On the 'real' or 'imagined' question...
Take a look at this animation, looking at a small segment of larger version.


Right in the middle there seems to be some large 'particles' that tumble and I'm guessing that their corresponding shadows are also visible against the 'lit' ring structure in the background. Thoughts?

[Bjorn Jonsson]

These images are amazing - I think they might be the most interesting images of the rings since SOI. Knowledge of the rings' 3D structure is about to be revolutionized. And let's not forget that these shadow will get much longer in the coming months.

Some quick 'back of the envelope' calculations: The solar elevation angle is ~1.9 degrees. Assuming that the shadows lie on a perfectly flat surface that is not tilted relative to Saturn's equatorial plane they are ~30 times longer than the height of the features that cause them. The length of the largest shadows is ~15 pixels. Assuming that the range is ~1.1 million km ("The camera was pointing toward SATURN-RINGS at approximately 1,138,888 kilometers away") and that Cassini is directly above the shadows (definitely not the case) the length of the shadow is ~100 km and the height of the feature casting the shadow ~3 km.

This is highly approximate but indicates that the highest 'peaks' are probably a few km high.

[Floyd]

Ring dynamics are slightly beyond me (I'm a microbiologist), but if we think in terms of large boulders or small moons, and the boulder-boulder gravity interaction is small, then each is in its own eliptical orbit. So a boulder we see highest above the ring plane/with the longest shadow will drop down to the lowest point below the ring plane 180 degrees later. If one assumed that the boulders' phase and inclination are all random, then you would have the boulders all moving around relative to one another, but you would need to observe them through about 90 degrees of orbit to see really significant changes--and then the shadows would have rotated 90 degrees. So the question is, what size changes could you see in 45, 22.5, or 11.25 degrees of orbit? A shadow could at maximum shorten or lengthen by sine of the angle. Maybe 22.5 degrees is small enough to keep track of shadows and register images and big enough to measure changes.
Any of you with real knowedge of astrophysics/ring dynamics--please correct my physics I reasoning.

[ElkGroveDan]

On the 'real' or 'imagined' question...
Take a look at this animation, looking at a small segment of larger version.
Right in the middle there seems to be some large 'particles' that tumble and I'm guessing that their corresponding shadows are also visible against the 'lit' ring structure in the background. Thoughts?

Astro0 I took the liberty of stabilizing your animated gif since I have found in the past (with one of Stu's originally) that the jumping around has a way of distracting from the actual changes.

A lot of it looks like it has to do with the lower resolving threshold of the optics interacting with the collector grid (or else the jpeg compression), but I do think I still see the "tumbling" effect on the larger particle right of center. It also might be a change of perspective among two or more visually aligned chunks, as the ring and Cassini pass each other. The full res images of this sequence whenever they are released will certainly be interesting.

Attached thumbnail(s)

 

[nprev]

I agree, Dan. There are certainly relative motion & differential illumination effects at work in addition to the performance limitations of the optics, and it's very hard to tell what's "real" from this raw data other than the shadows.

Definitely looking forward to more!!!

[Astro0]

Nice work Dan

I hope that we can look forward to even better images like these.

If all continues to go well, the XXM plans will certainly produce some exciting, close-up images.

[sci44]

[temporarily deleted]

[ugordan]

There is a story on UT now:-

http://www.universetoday.com/2009/04/12/ca...-saturns-rings/

Hmm. I wonder how this "scoop" will go by some imaging team members...

[ustrax]

Hmm. I wonder how this "scoop" will go by some imaging team members...

Well...EDITED: Let's wait and see...

[ngunn]

Don't miss Emily's great piece on this, with angles and heights. There must be quite a pile-up at the outer edge of that ring. Does it go all the way round?

I'm not normally a ring watcher, but this is the start of something not to be missed. It's eyes down for the magic shadow show.

[sci44]

Thats a fair point - I have nothing but respect for the work the Cassini imaging team, and they should get first stab at the data - I chopped my last post, but shall I just say I recommend N00133374.jpg as deserving close study (especially the left hand side of the region in question)..

[nprev]

Just because I felt like linking to a random recent image of the rings, here's one. Beautiful!!!!

[helvick]

I just read Emily's excellent blog post and I have to say that she makes a good argument for the shadow causing features being a couple of km in height. I also have to say that my earlier comment where I said I thought it was unlikely that we should expect to see motion was off base - I was ignoring the frame of reference and target of the camera and I was not factoring in the nature of the disturbance that Mimas would be causing. I'm very keen to find out what the Cassini team has to say about these shadows in any case.

[Stu]

Emily's piece on this is simply outstanding, a great piece of science journalism. It made this fascinating topic a LOT easier to understand for me. Thanks Emily!

( ... but then you go and ruin it by mentioning that ******* song at the end! It's 06.50 here in the UK right now, I'm just about to head out the door to go to work, and I know that tune will be going round and round in my head all freaking day now... !!! )

[Astro0]

Just to put one final piece into this thread, here's a rough stitch of the images across the rings.
I've left the moon shadow from each image for effect.
When everything is in context it certainly makes for a pretty picture.


Try rotating the image for a completely different feel on the shadows.

I'm starting to think that we were definitely 'seeing more' than is actually there.
But how fascinating is it to contemplate the day when Cassini does get a close enough view of the ring structure and with enough images together to 'actually see' the particles move.

Astro0