Bad Astronomy


Quick! Guess the planet!

OK, if you guessed Saturn then a) you’re smart, 2) you read the title of this post, c) you read the “alt text” of the image, δ) you saw that bare hint of ring in the corner of the picture, or 5) you had a one in 8 (or possibly 9) chance of getting it right.

But it is Saturn. It’s the equinox! This image, taken yesterday, is a raw one from Cassini. In other words, it hasn’t been processed to clean up bad pixels and take into account other weirdnesses of the digital detector. So you can’t do quantitative science on it, but what you can do is look at it and see how the shadow of the ring on the cloudtops is a thin, thin line. That means the Sun must be shining straight along them, like a tree casting no shadow at noon.

And that is exactly what’s going on. The ring particles orbit Saturn exactly above its equator, and that means that if you were standing on Saturn’s equator (or floating, I suppose) you’d see the Sun precisely overhead at noon. That’s pretty much the definition of “equinox”. It’s true on Earth, too.

The images are coming in from Cassini fast and steady, and it’ll be a few days before they can get all processed and pretty. So for now, check out more raw images from the magnificent machine, and as spring settles in on Saturn’s northern hemisphere, we’ll see lots more coming from Cassini.