Bad Astronomy

A little weekend Saturn awesomeness

If you need a little more awesome in your weekend, then try this:

I know I’ve been posting quite a few Saturn images from Cassini, but I really like this one. It shows the big round moon Rhea, the lumpy small moon Janus, and a lovely view of the foreshortened rings. Both moons were on the far side of the rings, well over 1 million kilometers away, when Cassini took this shot. Rhea is over 1500 km (900 miles) in diameter, while Janus is only about 180 km (110 miles) across. For comparison, our own Moon’s diameter is almost 3500 km (2100 miles). Just last year, the rings were edge-on to the Sun. In the months since, as Saturn slowly orbits our star, the Sun has begun shining down on the northern side of the rings. Cassini was just above the ring plane when it took this shot, catching the sunlight reflected off the rings. From this narrow angle, you can see the rings are divided into countless smaller ringlets, bright and dark sections carved into shape by the gravitational forces of the planet and its dozens of moons.

I love how the top of Rhea is playing hide-and-seek in the rings. And look how dark the rocky Janus is compared to the icy Rhea! Even at a glance you can see that Saturn’s environment is an amazingly rich and diverse place. Cassini’s observations will keep planetary astronomers busy for decades… and provide the rest of us with a glimpse of the beauty and awe just waiting to be uncovered.

Image credit: NASA/JPL/Space Science Institute

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Don’t have gravity? Take your lumps.
The real Pandora, and two mooning brothers
Cassini eavesdrops on orbit-swapping moons
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