On Earth, one way to watch the march of the seasons is to look for lengthening shadows as winter approaches. As the Sun gets lower in the sky every day, objects like trees and buildings cast longer shadows. On Saturn, there are no trees and buildings. There's not even a surface! So what do you do? Look to the rings:

[Click to encronosenate.] This image, taken by the Cassini spacecraft on August 22, 2011, shows the shadows of Saturn's magnificent ring system on the tops of the planet's cloud layers. Right now, Saturn is tipping its north pole toward the Sun, so summer is on its way there. But that means winter's approaching in the southern hemisphere, and shadows get longer. Saturn's rings aren't solid, but composed of countless particles of ice, probably no bigger than a few meters across at most, and the vast majority much smaller. There's also not just one big ring, but hundreds of thinner ones; from Earth, using small telescopes, they blur into what look like a handful of single rings. Big telescopes hint at the truth, but when you send an actual space probe there you see all those rings in their individual glory. Here, Cassini was almost in the plane of the rings, so direct details are scarce. But with Sun shining down on them, the rings' shadows make it very clear that when it comes to Saturn, there's just no substitute for being there. Image credit: NASA/JPL-Caltech/SSI

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