[X] My Assistant

[ugordan]

Here's a very short, grayscale Rhea flyby movie made up from 10 Cassini clear frames. The frames were reduced to 3/4 original size to keep the thing reasonable. One could arguably make a 3d anaglyph because the vantage point changes quite a bit. Note that the sequence is clipped a bit because Rhea was filling the entire field of view. There's a noticeable dimming of surface features as the phase angle increases.

 RHEA.mov ( 972.05K ) Number of downloads: 716

WARNING: Quicktime 7 and H.264 codec required!

[elakdawalla]

Cool comparison, ugordon. I'm not sure what it means, but it's interesting.

This reminds me that something I've been wanting to see for a long time is a composite view of Saturnian system bodies shown with the same processing applied across the board, to illustrate the differences (if any) in albedo and color among them. The mutual event shots make it clear that there are albedo differences among the grayer bodies such as Tethys, Dione, and Rhea. I'd love to see a montage of all the moons that would make clear their relative brightnesses -- seems like there should be enough photos available now to get a good set of views at similar phase angle to do this.

[ugordan]

This reminds me that something I've been wanting to see for a long time is a composite view of Saturnian system bodies shown with the same processing applied across the board, to illustrate the differences (if any) in albedo and color among them.

I've been wanting to see that as well, because as I was fiddling with the PDS data, I noticed there were stark differences between brigthnesses of various moons. I was too lazy to make a systematic comparison until now.

Below is a montage of the major moons -- except Phoebe, I couldn't get a darn good RGB set on the PDS.
All composites are approximately true color and use the same brightness scaling. I used Enceladus as the reference maximum brigthness.



The moons are from left to right:
Prometheus, Pandora, Mimas, Enceladus, Tethys, Dione, Rhea, Iapetus, Hyperion and Titan's limb on the right edge. All moons were scaled to the same scale, showing how they would appear to the narrow angle camera at a distance of 500 000 km.

A note on observed brightness -- it's a function of phase angle so I preferred a single phase angle or as close to it. It wasn't always possible, however. Notable exceptions are Prometheus and Pandora with phase angles of 10 and 19 deg, respectively. Other moons are at around 50 deg, except Dione and Rhea - 39 & 34 deg.

You may note that the leading hemisphere of Iapetus is practically invisible at this brightness scale. At albedo of around 0.04, the dark side is really pitch-black. Hyperion and Titan are very dim as well.

If I can dig-up a good RGB or IRGUV set of Phoebe, I might add it as well, but from what I've seen it's pretty gray and only slightly brighter than Cassini Regio.

[elakdawalla]

I've been wanting to see that as well, because as I was fiddling with the PDS data, I noticed there were stark differences between brigthnesses of various moons. I was too lazy to make a systematic comparison until now.

If you're lazy, what does that make me, sitting back here and dropping broad hints at work that I'd like other people to do for me?

Thanks for doing this. I knew there were differences but I hadn't realized just how different the albedos would be; I especially didn't realize just how dark Titan was. That's pretty cool. It looks like Tethys and Rhea are a little more reddish than Dione -- is that impression correct? If so, that's interesting too. Hmm. Neat stuff.

--Emily

[Guest_AlexBlackwell_*]

If you're lazy, what does that make me, sitting back here and dropping broad hints at work that I'd like other people to do for me?

I don't know but for some reason I'm reminded of Tom Sawyer Whitewashing the Fence.

I'm just joking, of course. At least you give credit, Emily, unlike, for example, Jim Oberg, who was (and probably still is) pretty effective at Tomsawyering his acolytes on USENET. Typically, he starts out with something like, "Hey, I'm working on a story about X and I need answers to the following fifteen questions. Thanks in advance, you guys are the greatest!"

[dilo]

It seems Cassini is dooing some astronomy sequences, here a registax sum of last four Narrow-angle images with removed (flattened) horizontal stripes:
(sum of N00064609+10+11+12)
Can someone guess where we are looking to?