The Cassini Saturn probe never seems to disappoint. This latest image is another stunner:

That image shows Saturn’s weird moon Mimas, which is uncannily like the Death Star, floating in front of Saturn’s magnificent rings. Cassini was pretty far out when it took this image; nearly twice as far from Mimas as the Earth is from the Moon.

I’ve written about Mimas before, but while poking around the web to find out more info just now, I found out that Mimas is not even close to being a sphere! Check this out:

That’s amazing! I had no clue it was so ovoid. This image exaggerates the effect somewhat, the top part of the moon as seen here is in shadow, so it makes Mimas look more egg-shaped than it really is. But the equatorial diameter is 10% larger than the polar diameter, which is a lot, given its 400 kilometer average diameter. Compare that to the Earth, where the equatorial diameter is only about 0.6% bigger than the polar diameter. The Earth is far more round than Mimas. Earth’s oblateness is caused by its rotation: basically, it’s just the centrifugal force^* making the Earth bulge. Mimas doesn’t spin nearly fast enough for that to be the reason. So I’m not sure why Mimas is so goofy looking (tides from Saturn? Maybe; it’s closer to Saturn than the Moon is to Earth). I’ll ask Carolyn Porco, leader of the Cassini imaging team, when I meet her at the Amaz!ng Meeting in January. Gloat gloat.

* Yes, the centrifugal force is real. Please don’t leave angry comments or emails here. The centripetal and centrifugal forces are the same thing, just seen in different frames of reference. People get all snarky about this, and I don’t know why. If you sit in a car that is making a turn, you darn well feel a force pushing you. If there were no force, you wouldn’t feel it. It’s really that simple.

Back in July, the NASA Deep Impact probe smacked into a comet, which was scientifically interesting, data-intensive, and downright fun. At the time, I was interviewed by Dr. Brian Cox about the Hollywood connection to the probe as part of a StarDate episode aired on the BBC. Brian and I connected well; he is interesting and funny and charming and (dagnappit) good-looking, and like me does a lot of public outreach.

Brian’s not the only one in his family who’s pretty cool. His wife, Gia, turns out to be a wholly engaging person herself. She’s hosted a few TV shows in the UK (her online video reels are hilarious), is a good photographer, and, it turns out, is also writing a blog for an upcoming science fiction movie called "Sunshine" which is filming in the UK (Brian is the science advisor). She decided to interview me for the blog, and that interview is now online.

It’s a bit scattered, but then I never found a topic I couldn’t carom tangentially off of. But mostly it’s about astronomy and science fiction, and me not letting Gia get a word in at all. That was probably a mistake; she is fabulous, and if she ever lets me interview with her again I’ll definitely (try to) let her squeeze a few words in. In the meantime, I’m thinking about the idea I had at the end of the interview on how to get a probe to the Sun. I may have to write up that idea before someone steals it…

Is that image from real footage of a meteorite impact in a desert?

Nope, but it’s pretty convincing! I’m getting a bit of email about it. The video clip in question (Quicktime format) seems to show a couple of guys in the desert filming their friends in a Toyota Tacoma truck. One of them says, “What’s that?”, and you can see a smoke trail in the sky. Suddenly, a meteorite slams into the ground a few meters away, right where the truck was! There’s an explosion, and the cameraman is knocked off his feet.

There are a few sites on the web that post weird or funny video clips, and this video can be found on some of them. Most of them have trimmed the last few seconds of the video off. However, if you find a site with the complete version, you’ll see the truck emerge unscratched from the explosion, and then a tagline appears: "TACOMA/METEOR-PROOF". That should make it clear this is just a put-on.

Since this is the Bad Astronomy Blog, I should point out that meteoroids that small won’t hit the ground with a huge bang, smoke, and fire. I wrote an article about this for space.com. Meteoroids that size slow down extremely rapidly high in the atmosphere, and take several minutes to fall the rest of the way to the ground at relatively low speed (maybe a few hundred miles per hour, compared to several thousand m.p.h. when they first hit the top of the atmosphere). Since they spend so much time way up in the atmosphere, where it’s very cold, they have plenty of time to cool off — especially since the heated outer layers of the meteoroid generally slough off while it’s still moving rapidly. It’s only really big meteoroids — many meters wide — that hit the ground while still moving quickly enough to generate heat.

And even then it’s no guarantee: while the impact that created Meteor Crater in Arizona was from the impact of a chunk of iron about 100 meters across, the explosion in Siberia in 1908 was an airburst, a rock that exploded many kilometers above the surface. So composition matters as well.

Note that I wrote that space.com article back in 2002. No one ever listens to me, though, so I expect this myth of hot meteor impacts to go on a long time. At least until a small meteorite hits CNN headquarters or some other news outlet. Then they’ll probably call it a comet.

Have you ever wanted to ask a famous science-type guy a question that’s been eating away at your brain for years?

Now’s your chance! Renowned scientist, author, and media go-to-guy Lawrence Krauss has agreed to participate in a Question and Answer session on the Bad Astronomy Universe Today bulletin board. Dr. Krauss studies such esoterica as multiple dimensions, dark matter, and, um, Star Trek.

If you have a question, it’s pretty simple: go to the BAUT board, register, and post your question in that thread (note: I will not forward comments from this blog; please go to the board if you have a question). Later this week we’ll send the best ones to Dr. Krauss for him to answer, so hurry! When we get his responses, we’ll post his answers for all to see on the board.

Note: due to the holidays and other personal reasons, this may be my last blog entry until next week. I’ll post more if I can, but no promises.

One year ago Sunday, the Swift satellite roared to orbit on top of an Delta rocket. Over the next few weeks, scientists and engineers gingerly activated the complex equipment onboard Swift that would allow it to fulfill its mission: to detect and observe gamma-ray bursts, flashes of high-energy light which appear to signal the births of black holes.

These bursts were one of the leading mysteries in astronomy for the past few decades. They would last as long as a few minutes, or as short as a few milliseconds. They would flash out their gamma rays, and sometimes — rarely — leave an afterglow in visible light. Gamma rays are notoriously difficult to trace; the best anyone could do was tell you kinda sorta where the gamma rays had come from, but it was difficult to get a good location for them on the sky. Without that, it was impossible to know what caused the bursts.

This was a real problem! It was difficult to imagine what could be causing these odd bursts. It was known they were happening very far away, billions of light years away. Earlier satellites had determined that. But the energetics of the explosions are truly awesome. They release as much energy in a few seconds as the Sun will over its entire lifetime. More.

But what physics lies at their heart? What could cause such vast explosions?

Swift, it was hoped, would solve that problem. It had the best hardware ever made for locating gamma-ray bursts. Once it pinned down the location looking at gamma rays, it would rapidly — hence its name — point its X-ray and Ultraviolet/Optical Telescopes at it, and nail the location very precisely. The coordinates were then to be beamed to the ground so that telescopes on Earth could follow-up.

When Swift launched, we had a lot of hopes riding along with it, hopes that this maddening mystery of GRBs would finally be cracked.

That was a year (and a day) ago now, and Swift has performed beautifully. It has seen dozens of bursts (roughly two per week, on average) and seen afterglows on quite a few. It has seen the most distant burst detected at a whopping 12.8 billion light years away. It has seen short and long bursts, bursts near and far, faint and bright (it caught a burst just last week that may have had the second brightest afterglow ever seen). The list goes on and on. You can even keep up with the latest bursts seen by Swift (and other satellites) on a website that updates this information in real-time: http://grb.sonoma.edu.

Swift has done so well that Popular Science magazine chose it as the Best of What’s New 2005, an award it richly deserves.

Swift is one of several satellites that provide funding to my group at Sonoma State University, and I’m proud to be able to talk about it in schools, at teacher conferences, in magazines, and of course on my blog. Swift has at least one more year in its mission, unless NASA decides to extend its mission longer. I think that’s a pretty good bet.

Happy anniversary, Swift.

This blog entry may strike some people as sexist. If you think so, then hear me now and believe me later, I will pummel you.

Because astronomy is for real men. Okay, fine, women, too. But wussies need not apply.

At least, I try to convince Mrs. Bad Astronomer of this. She’s skeptical. But professional astronomy isn’t for scaredy cats. Think about it: you’re up all night, which takes some stamina. You have to stay sharp, keep your wits. You’re around very large, heavy machinery which can be dangerous. There can be extremely caustic and scary chemicals involved (early exoplanet searches used hydrogen fluoride, a very scary chemical indeed). To top it off (literally!) you are usually on the apex of a very tall mountain, and observatories can be several stories tall, with easy access to the outside via a catwalk.

This is macho stuff.

Still don’t believe me? Well, then you should read the latest press release from the Keck Observatory. This premier observatory houses the giant twin 10-meter telescopes perched atop Mauna Kea — at an elevation of 14,000 feet. That is seriously way up there.

So far up there, in fact, it’s hard to breathe. What can you do? Well, as the press release notes, Keck just received a grant from the Hudson Foundation so they could buy air. The atmosphere is so tenuous at that height, that they need to ship in air just so people can breathe.

Now tell me again how astronomers are wimps. Take a deep breath of your mix of 78% N₂ and 22%O₂ at one atmospheric pressure so you can expound at length at how macho I am not. But don’t be surprised if I’m holding a 50 liter tank of liquid nitrogen behind my back, or an 80 square meter mirror, or a 64 megapixel camera, or a rocket capable of a million pounds of thrust to get my satellite orbiting the Earth. And don’t be surprised if I know how to use ‘em.

My toys are so better than yours.

Are those pesky government mind-controlling rays getting you down, forcing you to pay taxes, making you believe that Intelligent Design is an actual scientific theory?

Then do I have a paper for you! As only those wackheads at MIT can do, they tested the permeability and opacity of aluminum-foil hats to various emissions, to see how well they actually work to block any telekinetically-imposed outside behavioral patterns on an otherwise innocent population. And then they published their results!

They found that the hats do well blocking some transmissions, but surprisingly appear to have amplified some wavelength ranges of electromagnetic energy… suspiciously, a band reserved by the government for its own (presumably nefarious) reasons!

I think this was an interesting test, but they missed a very obvious problem: they used aluminum foil for their hats, and not tin, as they should have ("aluminum-foil hats" doesn’t have the same ring to it). Without this control, how can we know if we are safe or not? Perhaps someone at MIT reads this blog, and will do the obvious follow-up experiment. Don’t expect government funding, though.

Their results are nonetheless intriguing, and make me even more suspicious of any group who claim to make an off-the-shelf model.