Check this out! Cassini took a gorgeous shot of Titan casting its shadow on Saturn:

[Click to embiggen]

Wow!

A couple of cool things to note in this image… one is that the shadow is fuzzy. That’s because Titan has a thick atmosphere, so there is no sharp edge to the moon to cast a sharp shadow.

[Update: A few folks have pointed out that I didn't consider the idea that the fuzziness may be due to the fact that the Sun is not a point source, and so it will cast a fuzzy shadow -- this same thing happens during solar and lunar eclipses on Earth. I did some quick trigonometry, and I get that the fuzzy outer part of the eclipse shadow (called the penumbra) should be about 1000 km across or so, while the deep shadow (the umbra) is a little bit bigger than the size of Titan itself, or about 5200 km (again, these are pretty rough numbers). That jibes well with what we see in this image (if you neglect the weird distortion of Titan's shadow being stretched since it's projected on Saturn's curved cloud tops), so I'm now thinking that the shadow is not fuzzy due to Titan's atmosphere at all -- it's just the penumbra of this Titanic solar eclipse! I stand corrected, and I thank my readers for pointing this out. Very cool.]

Another is that even though Titan’s orbit is almost exactly in the same plane as the rings, its shadow is really far south of the rings’ shadow. That’s because spring has started in Saturn’s northern hemisphere, so the Sun is shining down on the planet from just north of the equator. The rings are relatively close to the planet surface, so the shadow they cast is just south of the equator (and narrow since the Sun is still shining nearly straight down the ring plane).

Titan orbits Saturn much farther out (1.2 million km from Saturn, very roughly 10 times farther out than the main rings on the average). Over that distance, the angle of the moon’s shadow carries it farther south of the equator. It’s a like a tall tree’s shadow being longer than a short tree’s shadow.

I’ve said it before, but it bears repeating: we will get a vast amount of science out of Cassini data, and learn more about Saturn in a few years than we have in all the centuries of observations before we launched the probe. But sometimes it’s just the pure beauty of the images that gets to me.

Tip o’ the tweet to Carolyn Porco.

If you were following Cosmic Variance yesterday, you saw its live blogging of one of the most anticipated recent announcements in physics: the team from Cryogenic Dark Matter Search (CDMS) telling the world whether a Minnesota detector spotted evidence of dark matter. The answer? Maybe (pdf).

CDMS scientists use super-cooled detectors made of germanium and silicon to search for weakly interacting massive particles (WIMPs), one of the leading suspects for what could make up dark matter. The detector is deep underground in the Soudan mine in Minnesota, which scientists also use to hunt for neutrinos. WIMPs streaming in from space would very rarely jostle the germanium nuclei, some 800 meters underground in the Soudan mine, generating a tiny amount of heat and slightly altering the charge on the detectors in a characteristic pattern [Science News].

In 2007-2008, CDMS researchers saw two events that could have been WIMP interactions. Because their calculations had suggested a likelihood of 0.8 jostling events for the two years just from radioactive decay of regular matter, that means there’s a decent chance—but far from a certainty—that they saw dark matter interactions. The team is not claiming discovery of dark matter, because the result is not statistically significant. There is a 1-in-4 chance that it is merely due to fluctuations in the background noise. Had the experiment seen five events above the expected background, the claim for having detected dark matter would have been a lot stronger [New Scientist].

Dark matter is the hypothetical stuff that physicists believe to be far more abundant than the matter that makes up you and me. It seems that ordinary matter – gas, stars, planets and galaxies – makes up less than 5% of the Universe. The remainder is unseen [BBC News]. Dark matter and dark energy—which is even more mysterious and plentiful than dark matter—constitute the rest, scientists think.

Next year the CDMS team will upgrade its detector for further experiments, and the bevy of scientists working with the Large Hadron Collider will be champing at the bit to use this new data when they resume their work in the new year, Dan Tovey of the LHC’s ATLAS project says. “The really exciting aspect of all this is that if you see a signal in a direct-detection dark matter experiment and a signal for supersymmetry at the LHC, you can compare those two observations and investigate whether they are compatible with each other,” says Tovey [New Scientist].

Related Content:
Cosmic Variance: Dark Matter Detected, or Not? Live Blogging the Seminar
Cosmic Variance: And the Eagerly Awaited Dark Matter Result Is…
80beats: More Circumstantial Evidence for Dark Matter, But the Debate Continues
80beats: Does a Shower of Subatomic Positrons Mean We’ve Found Dark Matter?
DISCOVER: 8 Ways Scientists Look At—But Don’t Yet See—Dark Matter

Image: CDMS

There is a really good piece up at the Yale Forum on Climate Change & The Media that looks at the top five most prominent issues raised in “ClimateGate”, analyzes the relevant emails in context, and finds some concerns but not much wrong–with the notable exception of the suggestion that emails subject to a Freedom of Information request be deleted. The article’s author, Zeke Hausfather, concludes:

It is unfortunate, if perhaps not surprising, that the quotes from the e-mails that have gotten the most publicity from skeptics and in some media strongly distort the views and actions of the scientists in question, contributing to a perception of collusion to manipulate the climate data itself.

Nothing contained in the e-mails, however, suggests that global temperature records are particularly inaccurate or, worse, that they have been manipulated to show greater warming. The certainly troubling conduct exposed in some of the e-mails has little bearing on the fundamental science that strongly indicates that the world is warming and that anthropogenic emissions of greenhouse gases are the primary cause.

You should read the whole piece, for it clearly and soberly shows just how much this has been blown out of proportion.