This morning, I wrote about some pictures of Saturn's moon Enceladus I found rummaging through NASA's Cassini raw images archive. Enceladus is a small icy moon that may have an ocean of liquid water under its surface. It's a fascinating world, and is one of those objects that cannot seem to take a bad picture; every shot of it is dramatic and intriguing.
Even so, as I clicked through the raw images from the distant spacecraft, I got a jolt when I stumbled on a series of pictures depicting the tiny disk of Enceladus with the gigantic visage of Titan sliding past! I quickly grabbed the images and made a short animation showing the scene, with a description:
[It helps to watch full-screen and in hi-res; I recorded it in 1080p. The images from Cassini look pretty good that way.]
Nifty, eh? I'll note that in between some of the frames of the animation Cassini was programmed to change filters. That's most obvious by looking at Titan itself; when the blue filter was used the atmospheric layers become more obvious -- an upper level haze layer is dark in blue colors. Here's one of those images using the blue filter:
You might wonder why the picture isn't blue if a blue filter was used. That's because the detectors used on spacecraft (and most telescope) cameras don't really detect colors, they only detect light. Astronomers use filters to block out or isolate certain colors of light, say red, green, or blue. Each of those individual images is really just an array of numbers, so an individual filtered image can only be displayed as a grayscale picture like the one above. It's when you add the three images together that true color emerges. The actual process is pretty detailed, but that's the boiled-down version.
And you can do this too, if you want. The raw images are freely available to anyone, and it's fun to poke around the archive. For these specific shots, go to the archive, search on "Narrow Angle", set the target to Enceladus, and look between the dates 09/17/2011 to 09/20/2011. You'll find 'em. But you can find amazing things if you widen the search parameters, too. Find the shots of Hyperion to get a real dose of weird... Also, the folks at Hubble have a great tutorial on how to assemble individual images into a color picture.
There are astonishing shots in there, and if you're American your tax dollars paid for them. But they belong to all of humanity now, as well they should. There are scientific treasures in there, and I know people will be mining that data for decades to come.
Image Credit: NASA/JPL/Space Science Institute
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