Okay, this just proves I’m a whore for astronomy images. I’d already started writing something about PET scans in relation to today’s story about the long-term effects of chemotherapy on brain function, but then I saw the press release for the above image.

In spite of the mediocre resolution (mostly because it’s a composite of infrared mapping spectrometer, which operates in a scanning, single-pixel-at-a-time mode), the image rather intuitively communicates the idea of seeing ”through” Saturn’s clouds.

As described in the caption from JPL, we’re looking at a near-infrared image of Saturn, in which the shorter-wavelength light (shown as blue-to-green) is reflected off the cloudtops whereas the longer-wavelength emission (colored red) from Saturn’s warm interior shines through in shadowed regions, less obviously in the daylit regions. Because most people (stellar astronomers excluded) think of red as warm and blue as cool, this image capitalizes on people’s natural sensibilities. Always a good thing.

This strikes me as a good image to talk about some of the confusing aspects of infrared light, which well-informed people typically perceive simply as “heat,” because that’s what they’ve been told. Of course, the problem with blackbody radiation is that there’s a big contrast issue: yeah, the lower layers of Saturn’s atmosphere may be warm, but their infrared glow gets blocked by clouds in the upper atmosphere, plus it has to compete with the bright, reflected glare of the Sun. The image above allows one to talk about those contrast issues while clearly conveying that infrared light allows us to see things we can’t in visible light. Also, the rings cut across the center of the image as a blue line, indicating that they reflect the short-wavelength infrared light but don’t emit much thermally—pretty much as one would expect from chilly rings made mostly of ice.