[Click to explodenate.]

The three panels show a 1986 test of a Tomahawk cruise missile. The missile traveled 640 km (400 mile) low over the terrain to detonate above the target, a decommissioned fighter plane. It’s pretty clear the test was a success.

But what caught my eye immediately was the middle panel. Let me zoom it for you:

[Click to hugely embiggen!]

Now look carefully there. When the missile exploded, the expanding debris cloud from the vaporized weapon was probably moving faster than the speed of sound. Even so, in this second picture you can see none of it had touched the planet yet when the shot was snapped.

Yet look at the plane: it’s on fire. How can that be?

It’s because of something that moves much faster even than supersonic debris: light. When the warhead exploded, it sent out a huge pulse of heat in the form of infrared photons, light that travels about a million times faster than sound. As far as that flash of heat was concerned, the expanding debris was standing perfectly still! There was plenty of time for that heat to get to the plane and set it aflame before the explosion itself could reach that far.

Note that third picture, taken from an oblique angle. You can match the features in the fireball to the ones in the second picture. The ground around the plane is lit up by the blast, and again no debris had yet reached the plane itself.

It’s a little counterintuitive that the explosion works this way. We think of explosions as being made of expanding stuff, but it turns out that light has its role to fill as well. In fact, this is important in other ways: one idea to push Earth-crossing asteroids out of the way is to light off a nuke nearby. The force of the explosion itself isn’t all that great in space, because there’s no air to create a shock wave. The only momentum you give the rock directly is the expanding debris from the bomb itself, which isn’t all that much. But the blast of heat/light is immense, and can heat the asteroid past its vaporization point. The flash-vaporized rock expands, pushing on the asteroid like a rocket motor.

Unfortunately, modeling of this shows it doesn’t work terribly well compared to other methods (like simply slamming the asteroid with a space probe like a linebacker hitting a quarterback). Still, you need to consider all the details when thinking about things like this. The devil hides in them, y’know!

Oh, and one more thing. This Tomahawk test was done 24 years ago. How much has the technology improved since then?

Yikes.

If you’re not subscribing to their podcast, you are most definitely missing out. It’s a lot of fun, and I bet you’ll learn something while you’re enjoying yourself.

In a recent post about comets, I mentioned her and a project she and a bunch of other grads are working on: Dark Skies, Bright Kids. This is a terrific project that is doing a lot to bring the joy and wonder of astronomy to third graders in Albemarle County, the home of UVa (if you saw my show "Bad Universe" where I made the comet, I got that recipe from Nicole and DSBK!). One of their efforts is a bilingual book designed to make astronomy fun for the kids — I have a copy, and it’s very cute; as someone who has worked on astronomy education I know kids that age will love it. Nicole and her group have a big goal for the book, too: they’re looking to get a copy of it into the hands of every single third-grader in the county.

To do this, they applied for a Pepsi Refresh Grant, which, if they win, will get them $25,000! And you can help: all you have to do is go to the page and click a link to vote for them. To be fair, surf around and look at the other applicants if you want; there are other worthy efforts. But I’m voting for DSBK because I know how important it is to get kids to look up and have a sense of wonder about the Universe around them.

They also put together a short video of the children having fun while learning science:

Voting is open now, closes September 30, and once you sign up you can vote once per day. Thanks!

So why don’t we see all these alien spacecraft? I think this is because we almost always understand what we’re seeing in the sky, so we know not to mistake Venus, the Moon, a satellite, or other mundane things for flying saucers.

While UFO believers love to make hay of this — showing me the extremely rare time when an astronomer has reported a UFO, thus proving my point, or falsely saying astronomers spend too much time at the eyepiece to note the broader sky (which is ridiculous) — the fact is, astronomers are familiar with the sky, so we know what’s going on.

Well, almost always know. John Woolley of the Greater Edmonton Skeptics Society has an amusing story of the time he and some other astronomers saw something they couldn’t immediately explain… and make sure you read Part 2.

And y’know, his story sounds pretty familiar…

So remember, despite the claims of the UFO crowd and the media that love to play this stuff up, seeing isn’t believing. Understanding is!

- My brother from another mother Fraser Cain at Universe Today

- My alma mater’s online mag UVa Today

- Gotham Skeptic

- The Bollingbrook Babbler (that’s a satirical newspaper, so there ya go)

- Hey Freqs!

- Pop Army

- My friend Evan Bernstein from Skeptics’ Guide to the Universe wrote up his thoughts at The Ness

- I started a thread on Reddit

- The science and scifi blog io9

The reviews are all still very positive, which makes me happy, since I can send the links to Discovery Channel instead of pestering them myself. If you know of more reviews, please link to them in the comments below! If you find a negative one, don’t hesitate to link to it; I want to know what people think so we can make the better… if we get that chance.

A lot of folks are asking when it will play in their country. I don’t know, except that Discovery Asia will air it in November, and Discovery Canada is looking into it – and that latter was due to people on Twitter asking them. So don’t ever think you can’t influence what gets aired on TV, folks. Power to the Tweeple!

I’ve known Jennifer for a couple of years now. She helms the Science and Entertainment Exchange (trying to get better science into movies), she spoke (wonderfully) at TAM 7, she was at SETIcon and Comic Con, and I also know her through her husband, cosmologist Sean Carroll — he blogs for the Hive Overmind at Cosmic Variance. Jennifer writes the Cocktail Party Physics blog and for the Discovery Channel blogs, too… and I am not ashamed to admit I have a wild crush on her avatar, Jen-Luc Piquant. So I was really excited to get my hands on an advance copy of her book, especially since I knew she could handle the topic well.

It was everything I had hoped for. Yeah, look, I know: it’s a book about calculus. But it just so happens to be a really good book about calculus! It’s not equations and homework — well, OK, there are equations — it’s really stories and fun and personal tales punctuated with how calculus gives us insight into the backstory. I know a bit of math, but didn’t know that calculus can be used to describe the Dutch tulip boom of the 17th century, or why you may not need to worry about a zombie horde (because by the time you know it’s happening, it’s too late to do anything about it except start getting used to shambling and eating brains).

Jennifer uses her great writing style to make these ideas easy to read and fun to think about. I suspect that if you like my blog, you’ll like this book. If math terrifies you then you can skip over the equations (though honestly, you’re missing out), and if you like the math you’ll love the way it gets applied here.

All in all, I recommend it. If you hurry, you can still read it on the beach during these last days of summer… or get her to sign it at Dragon*Con next week!

P.S. There’s a Facebook page for it, too.

This time it’s a metro-subway-style map showing scientists of the past 400 or so years. It’s wonderfully detailed! Here it is shrunk enough to fit on my meager 610-pixel wide blog:

[Click to unsubwaynate and get the 2Mb 4500 x 2700 pixel version.]

Each color track route represent a field of science – brown is chemistry, red is theoretical physical and quantum mechanics, and so on – and the time is concentric, with the 16th Century in the middle, and current time on the outside. Just like a subway map where there are transfer points, some people span more than one discipline, and you can see that as two circles connecting different tracks. Stephen Hawking, for example, is astronomy and physics. Here’s a zoom:

Cool, huh? Galileo was clearly a man of many hats. Lots of other scientists straddle multiple fields, but interestingly, the number of them dwindles with time. I’m no science historian – I’m not sure science existed before Twitter – but I imagine there are many reasons for this, not the least of which was that when science as a method was new, it was easier to make grand discoveries that spanned many different disciplines. It’s just plain old harder to do that these days. To make a name for yourself you have to be pretty good in a narrow field, and very few people have that sort of polymath capability when modern science is so deep and rich.

Note that for the 20th Century, Crispian started including a lot of popularizers of science as well. There may be a few names you recognize…

I expect this map will go viral once places like Geekologie and Boing Boing find it. Which they will. Get in on the coolness on the ground floor now. Or, of course, one flight lower.