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Emily LakdawallaFebruary 25, 2014

A little fun with Cassini rings images

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

NASA / JPL / SSI

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

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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Emily Lakdwalla
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