A Fine Aerosol Diagram

New results from the Cassini spacecraft reveal the chain of events (so to speak) that leads to the formation of complex aerosols in its atmosphere. Aside from the spiffy science, the NASA announcement includes the very nice diagram pictured above.

What I like about the graphic is that it tells the story very plainly and simply, yet with considerable detail and substantial visual interest: nice little PAHs and aerosols, decent image of Titan’s surface, Saturn in the background (tilted too much with respect to the ring plane, but that’s nothing new), and so on. It even includes altitude info on the right-hand side clearly indicating where specific processes take place. All in all, a lot of info packed into a single image.

And anther detail. I’m already on record as not being a fan of lens flares in the fulldome environment, and in general, I seem them as kind of cheesy. But this might be the first time I’ve seen a lens flare used as a didactic element, suggesting the flow of photons from the Sun. Nice touch!

The only thing that gives me pause is the depiction of “energetic particles” as little arrows pointing away from Saturn. The particles are trapped in Saturn’s magnetic field, so they aren’t really shooting out of the planet in straight lines, which makes that depiction a little deceptive. But then, the only real solution would be to depict Saturn’s magnetic field with particles streaming from it, and that might be a little cumbersome. So I suppose I can forgive the diagrammatic shorthand.

Another more mundane quibble. The NASA webpage for the diagram include links to smaller versions at 1600×1200, 1028×768, and 800×600, but those are all windowboxed versions of the (obviously portrait, not landscape) diagram. Thus, the only version of above image that you can download at its original aspect ratio is the full-resolution version: a whopping 2000×2776 pixels! Not the greatest for, say, linking to blog entries.

Anyway, nice work, Cassinifolk! I like the diagram. And the story it tells…

Bent Light, Broken Caption

Too much to blog about! I’m getting backlogged… And just to complicate matters, here’s a new graphic from the European Sapce Agency that’s too much to pass up.

The image above shows Titan, Saturn’s largest moon, as seen in a slightly odd mix of visible and infrared light (if you really must know). The white line beneath Titan shows a “light curve,” which represents the intensity of light on the vertical axis, time on the horizontal axis, indicating the brightness of the star measured as it “passed behind” Titan through a trick of rotational and orbital dynamics in our solar system. The dimming of the star as it passes behind Titan reveals information about the moon’s atmosphere, and the peak of light in the center shows that the atmosphere acts like a lens, focussing light from the opposite side of the planet. The press release goes into some detail about how much we can learn from such observations, right down to predicting a bumpy ride for a spacecraft!

Now, I won’t claim my explanation above as the be-all-end-all, but I think the caption on ESA’s page doesn’t offer enough information about what’s going on in the still image. It never explains the term “light curve,” for example. I understand the reluctance to put words on the graphic (not so much for NASA, but for ESA serving a multilingual constituency), but the caption should compensate.

The animation of the graphic shows what’s happening much better, and I imagine the still image will make sense to people once they’ve seen the animation. N.B. that the caption for the animation is the same length as the caption for the still image—a stylistic requirement, I’m guessing. But the still image, with so much less information in it and so much more information implied by it, requires more verbiage to support it.

Was Lost But Now Am Trouvelet

Browsing through the New York Public Library (NYPL) Digital Library collection, I ran across Trouvelot’s drawing (well, chromolithograph) of the planet Saturn, as observed on 30 November 1874. A beautiful drawing at first glance, but as I looked at it more, I grew troubled. Care to guess what troubled me?

Aside from being (at least partially) responsible for introducing the gypsy moth to North America, Etiene Leopold Trouvelot worked for the Harvard Observatory and executed numerous drawings of “celestial phenomena as they appear to the trained eye and to an experienced draughtsman through the great modern telescopes.” A search through his drawings available from NYPL shows some pretty psychedelic stuff (check out his voluptuous, almost sexual sunspots), but given that astrophotography was still in its infancy, it makes sense that “an experienced draughtsman” would be given the task of reproducing what was seen through the eyepiece.

I have previously blogged on the challenges of using artwork as a basis of scientific communication, but I’m surprised by a major failing of this image—namely, the depiction of Saturn’s shadow on its rings. From Earth’s perspective (and presumably, Trouvelet was observing from a terrestrial vantage point), the Sun always appears to “our back” and Saturn’s rings look basically fully lit, with only a sliver of shadow at most—the highly angled, asymmetrical lighting shown in the image above simply isn’t possible. Furthermore, the shadow doesn’t appear to fall from the disk of the planet (it doesn’t line up properly), and it also suggests that the rings are not planar.

Given what was known 125 years ago about the solar system and Saturn, Trouvelet should have known better than to draw Saturn in this manner. It’s totally non-physical! And this is after he’d been working for Harvard for two years! And even if Trouvelet thought it appropriate, why would the astronomers for whom he worked allow such images to be printed?

I’m terribly confused…

This guy walked off with the Valz Prize from the Académie Française (whatever that is)? He even got a lunar crater named after him? And what exactly was his contribution to science? On the one hand, I would hope that he could have let go of some of his self-imposed prejudices (e.g., his art-deco Mars or his ouija-board meteors), but on the other hand, I wish he could have imposed more common sense on his drawings as well. Perhaps those are mutually exclusive, but looking at Trouvelet’s work, is it difficult to understand why people believed there were canals on Mars?

In Saturn’s Shadow

It’s tempting to do a simple report from the Astro-Viz ”06 workshop, since we’re starting to have conversations that might be of interest, but David Malin distracted me by presenting the above image as part of his keynote address this morning.

The Photojournal description of “In Saturn’s Shadow” tells us that the image “was created by combining a total of 165 images taken by the Cassini wide-angle camera.” We can see light scattered through the rings, as well as light cast on the dark side of the planet by the rings themselves. Obviously, one gets a sense of the extended nature of the rings as well.

“Color in the view was created by digitally compositing ultraviolet, infrared and clear filter images and was then adjusted to resemble natural color.” A sentence that gives me pause. I appreciate the description, but I’d like a little more detail (even if I think I can piece together what’s going on anyway). And the annotated image doesn’t help.

The corresponding page from the CICLOPS site provides a little more detail, describing color variations in the E ring in the “color-exaggerated” image above. Maybe there could be a link to a page describing what “color-exaggerated” means? Basically, I think they’re just trying to acquire a longer baseline (in terms of wavelength, stretching from ultraviolet to visible to infrared), thereby enhancing color contrasts.

Spiffy image, that’s for sure. Very spiffy. And it speaks to one of the points Malin made this morning: that compelling images can simply make one look more closely and phenomena, which excites curiosity and promotes thinking about the cosmos.

Speaking Warmly of Saturn

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.

Speaking of a Pale Blue Dot…

I referenced this image in my Yahoo 360 blog, but it’s worth presenting again. Taken by the Cassini spacecraft (currently in orbit around Saturn), it shows Earth as a point of light viewed through Saturn’s rings. You can read more about the image on NASA’s Cassini page. As Carl Sagan wrote, regarding a similar image: “Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light. Our planet is a lonely speck in the great enveloping cosmic dark. In our obscurity, in all this vastness, there is no hint that help will come from elsewhere to save us from ourselves.”