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See other posts from February 2014

Headshot of Emily Lakdawalla

A little fun with Cassini rings images

Posted By Emily Lakdawalla

2014/02/25 06:51 CST

Topics: pretty pictures, Cassini, amateur image processing, Saturn's rings

It's happened again; I went into the Cassini image archive looking for something specific and wound up spending several hours playing with totally unrelated image data. There are just too many images in there, and all of them pretty. I was struck by this one, showing Saturn's shadow falling on the rings. We're looking at the unlit face of the rings (that is, the Sun is lighting them up from behind), which is why the F ring appears so bright. If you can't quite picture the geometry, here's a link to the Solar System Simulator that may help.

Rings rising from Saturn's shadow

NASA / JPL / SSI / Emily Lakdawalla

Rings rising from Saturn's shadow
Saturn casts a fuzzy shadow on the outer edge of its rings, which are lit from behind in this view. They have just rotated into sunlight.

I love the images of the rings that were taken in 2009, around the time of Saturn's equinox. The rings are essentially a flat disk so ordinarily they appear pretty much the same brightness all the way around, at a given distance from Saturn. But near equinox, the rings got so dark (because they were being lit at such a low angle by the Sun), that Saturnshine became an important light source for the rings. And of course Saturnshine is much brighter at the longitude that's close to noon on Saturn.

Saturn's rings near equinox

NASA / JPL / SSI / Emily Lakdawalla

Saturn's rings near equinox
Close to equinox, the Sun shone from a very low angle on to the rings. In this view, the rings appear brighter at upper right, where they are strongly illuminated by Saturnshine.

Sometimes images are marred by blemishes that make them accidentally beautiful. Here's one that was taken close enough to the Sun that there's a lot of stray light blasting the scene. It's especially pretty here because those light rays weren't in the same positions in red, green, and blue-filter images, so the color combination appears to be in some kind of rainbow light bath. Either that or the rings are casting a rainbow light spell out into space.

Looking at the rings, close to the Sun

NASA / JPL / SSI / Emily Lakdawalla

Looking at the rings, close to the Sun
Cassini gazed at the unlit side of the rings with the Sun just above the field of view. The wavy lines in the background are caused by sunlight leaking into the camera.

Finally, here's a great accidentally beautiful image. It was taken at nearly the same time as this famous "In Saturn's Shadow" portrait, but at a time when the Sun was not blocked by the planet. The Sun dominates the view, and adds a couple of lens flares for good measure.

Accidental beauty: the Sun and Saturn


Accidental beauty: the Sun and Saturn
This photo was taken just after the famous "In Saturn's Shadow" portrait of Saturn eclipsing the Sun, when the Sun had emerged from behind Saturn, on September 15, 2006. The image has not been processed except for calibration.

Read more blog entries about: pretty pictures, Cassini, amateur image processing, Saturn's rings


Stephen Van Vuuren: 02/26/2014 10:50 CST

Lovely images - nice work!

Vicente L Ruiz: 02/26/2014 04:55 CST

Those images are fantastic! So much so they make me ask one question: what's the Copyright state of your images? I know NASA's content is almost always public domain, but these are modified by you.Can they be used freely? Thanks for your work. It means a lot for many people.

Vicente L Ruiz: 02/26/2014 04:56 CST

OK, I've already found the answer to my question... So forget about it and just keep my praise!

Enzo: 02/26/2014 04:59 CST

Could Cassini ever resolve the rings (i.e. take a picture that shows at least the largest particles individually) ? I often wondered about this and decided to do a bit of research. Apparently the biggest particles are ~10m. Cassini imaging system has a max field of 0.35 degrees on a CCD of 1024x1024 pixels. See here : So the max resolution is 0.35/1024=~3.4e-4 degrees per pixel. So, what is the distance at which a 10 m object angular size is ~3.4e-4 degrees ? If the object size is S, the distance D and the angle A (in radians) : S/D=tan(A) with S = 10 m and A=~6e-6 (~3.4e-4 degrees in radians) The distance is ~1676 Km So, if Cassini ever gets closer than 1676 km from the rings, it might be able to resolve the largest particles. Well, maybe < 1000 Km. Will this happen and will the spacecraft be in a position to take pictures (i.e. not busy with some other activity or too fast, whaever) ? I don't know, the most likely opportunities seem to be at the end of the mission where it passes between Saturn and the rings. If it doesn't get axed that is. Maybe someone from Cassin's team could tell us if this is possible.

Emily Lakdawalla: 02/26/2014 05:42 CST

Wow, two commenters answering their own questions -- that is awesome :) In case others share Vicente's question, if you click on most images on this site you'll be taken to a page that explicitly lists copyright information. Most of my processed images I share with Creative Commons NC-BY-SA meaning (briefly) you can use it as you like for noncommercial purposes as long as you give me credit. Works by other people on this site may have the same or different restrictions. Enzo: The problem is that if Cassini is close to the rings, it is by necessity also close to the ring plane. It can't get as close as 2000 km from a very big particle without risk to the spacecraft. It was closest to the rings during orbit insertion (when it passed between F and G rings, and will be close again during the proximal orbits, but these are all rings made of tiny particles -- the big particles are in the B ring, which Cassini can't cross without death. One way it has "seen" individual particles is with radio occultations of the rings.

Enzo: 02/26/2014 06:59 CST

Thanks Emily, I guess it's not possible with the current scheduled orbits. To fly over B at < 1000 Km would require to orbit Saturn at a very shallow angle (

Enzo: 02/26/2014 07:01 CST

Not sure what happened to the rest of the post, but I wanted to link a past proposed mission that would have imaged particles down to 1 cm ! :

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