The Tunguska Explosion took place on June 30th 1908, exactly 100 years ago today. Although it is almost certain that it was the result of an small asteroid or comet exploding in the atmosphere with an estimated yield(*) equivalent to 20 million tons of TNT (i.e. over a thousand times more energy than released by the atomic bomb dropped on Hiroshima), many mysteries still remain.
Scientific American had an interesting article on Tunguska in its June 2008 edition, on the search for a crater. Space.com has another article worth a look, which has some fun at the end by mentioning some of the more outlandish hypotheses put forward over the years: an alien space ship blowing up, a mini-black hole passing through the Earth, or Tesla's experimental death ray.
(*) The explosion of 1 ton of TNT is equivalent to the release of 4.18e9 Joules of energy (see here), so roughly the Tunguska explosion was about 8.4e15 Joules, or 8.4e22 ergs. By way of comparison the luminosity of the Sun is 3.845e33 ergs per second.
[The image is of trees flattened by the explosion, taken twenty years afterwards by the Kulik expedition. Source: APOD for 2007 November 14]
Monday, June 30, 2008
Friday, June 27, 2008
Shaviv at DailyKos provides an interesting summary of the unhappy history of nuclear powered aircraft designs, featuring the Convair X-6, the XB-70 Valkyrie (very 70's looking, as you can see from the Wikimedia Commons image, but still a beautiful bit of technology), and the un-manned nuclear ramjet Project Pluto.
Is anyone currently thinking big and trying to make ambitious outside-the-box stuff like this?
Posted by Dave Strickland at 12:10 PM
Thursday, June 26, 2008
A variety of media outlets are reporting on a series of new papers that strengthen the case that the peculiar differences between the northern and southern hemispheres of Mars (e.g. see this topographic map of Mars, or this web page) are due to a very large impact by a proto-planetary object of order 1000 miles in diameter.
Kenneth Chang discusses this in an article in the NYT, although he awkwardly calls the impactor a "meteor." Clara Moskowitz at Space.com also discusses the story, as does JR Minkle at SciAm news (see if you can spot the mistake in the image caption accompanying the SciAm article).
[Image shown is a color-coded map of the elevation of Mars, from the Mars Orbiter Laser Altimeter, showing the low, smooth, northern hemisphere and the higher, cratered, south. Note that even recently (1999) this data was used to argue against an external cause for the north/south dichotomy.]
Posted by Dave Strickland at 7:46 PM
Wednesday, June 25, 2008
[Warning: This post is all about politics, and reflects the personal opinions of the writer. Don't read it if politics offends you.]
According to this SciAm podcast by Christie Nicholson ("Why are conservatives happier than liberals?"), new research investigating the reasons for why previous polling shows that conservatives tend to have greater subjective well-being than liberals has found that:
conservative belief acts as a psychological buffer in a world of increasing inequality. The idea is that conservatives tend to rationalize inequality as the result of a fair process in a meritocracy, whereas liberals tend to see inequality as inherently unjust.Hum. Skeptical would be an understatement of how I feel about this sort of thing. This is exactly the sort of thing that makes the "hard" sciences look down on the the so-called "soft" sciences like psychology (despite them doing good science at other times).
Some polling is hardly a great empirical basis on which to base a result that one then seeks to elevate to a facet of psychology worthy of explaining. Polling depends heavily on exactly what questions are asked and what responses are allowed, is subject to all sorts of annoying sampling biases, and even then we know people's responses may not be entirely honest or robust.
Now there may be some truth in the quoted result - or at least it reinforces widely-accepted liberal views of conservatism. My favorite is a quote from John Kenneth Galbraith:
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness.
Yet while this may be true in part, the input hypothesis accepted at face value in the research quote in SciAm - that conservatives are "happier" than liberals - is fundamentally one-dimensional and overly simplistic.
Anyone who has paid attention to politics in the last few decades (or has read conservative blogs such as Free Republic, Red State or LGF) will have seen that modern conservatism is strongly energized and supported not by superior subjective well being, but by anger and fear. The conservative voting base in the Western World is worried and unhappy about (and goes to vote against) women's increasing control over their own bodies, peoples increasing wish for freedom and rights regarding their own sexuality, increasing ethnic and religious diversity, and the erosion of the old white protestant domination of social, economic and political spheres.
Yes, there are many conservatives who are purely economically motivated, the (often undeserving or deliberately unethical) over-privileged wealthy, who personify the deliberate smug self-satisfaction described in the article. These people may even control their political parties.
But rank-and-file conservatives are not the happy go lucky caricatures presented in the cute 60 second podcast. I don't think I've ever met a conservative who wasn't deeply unhappy about some imagined societal injustice or social crisis. So for now I'll just take this latest take on "happy conservatives" with a big pinch of salt.
Posted by Dave Strickland at 8:51 AM
Fedy Abi-Chahla has an interesting (if lengthy) article at Tom's Hardware on using Nvidia's CUDA library to do high performance mathematical on a GPU instead of the CPU. I've mentioned this concept before, but Abi-Chahla's article goes a lot deeper into the nitty gritty of the mechanics of it all and demonstrates an actual example.
Posted by Dave Strickland at 8:46 AM
If this post could have a subtitle it would be "The stupid, it burns!"
I must confess a shameful interest in the actual mechanics of the computing I rely on to do science. A lot of astrophysicists proudly ignore the details of technology, blithely purchasing whatever hardware seems popular at the time (Sun workstations and Windows laptops a decade ago, Mac Pros and MacBook Pros now), but I enjoy reading the occasional Tech web site, because you can often actually learn something valuable from them.
Occasionally even reputable Tech sites will post absolute idiocy, and it becomes apparent that not everyone who has access to a computer actually knows or wants to think logically.
This week Real Climate has to take the time to deconstruct a simultaneously amusingly and depressingly stupid set of articles in Wired that argue that air conditioning is green than heating and that tree farms are greener than keeping old growth forest.
Pretty obvious isn't it? If you came up with the answer that it takes less energy to cool something in a heat bath down by a fixed amount than to heat it up by the same amount you might want to check your calculations, because you would remember this rather fundamental thing called the Second Law of Thermodynamics.
Yet Matt Power, the article of those Wired articles, didn't even blink an eye before publishing them. I can only presume he skipped his physics classes while he was registering Republican. Looks like Wired's Matt Power is their equivalent to Daily Tech's Michael Asher.
Posted by Dave Strickland at 8:20 AM
Friday, June 20, 2008
In a surprisingly bi-partisan decision (409 to 15) the House overwhelming voted more funding for NASA, despite Bush's stated opposition (AP story here).
Part of the extra funding goes toward an additional Shuttle launch that will take the Alpha Magnetic Spectrometer to the Space Station. Seeing as a lot of money has already been spent on building the AMS and storing it in a warehouse near DC for the last few years, actually using the thing is good for the both the tax-payer and science.
[Expanded diagram of the AMS-02 detector image from http://cyclo.mit.edu/~bmonreal/detector_intro.html ]
Posted by Dave Strickland at 10:16 AM
Wednesday, June 11, 2008
Yesterday's NYT (June 10th 2008) had an interesting article by Cornelia Dean about the three Physicists in the US Congress and Senate (two Democrats and one Republican, in case you are wondering).
There are 435 people in the House, Mr. Holt said, and “420 don’t know much about science and choose not to.” He recalled his exasperation when anthrax spores were discovered in the Capitol in 2001 and colleagues came to him and said, “You are a scientist, you must know about anthrax,” a subject ordinarily missing from the physics curriculum.
“The difference,” he said, “is we would be perfectly happy to pick up a copy of The New England Journal of Medicine and read about the etiology of anthrax.”
“In fact, we basically did that,” Mr. Ehlers said.
“We know more than our colleagues,” Mr. Holt said, “but not more than they could know.”
Unfortunately, Mr. Foster said, “unless things play to their advantage in the next election, they are not interested.”
Posted by Dave Strickland at 9:26 AM
Friday, June 06, 2008
Tuesday, June 03, 2008
Maps are magical things: they contain both knowledge and mystery.
Modern maps may not explicitly show monsters drawn on the unexplored parts of the map, but we're free to put them in ourselves.
And maps are often wrong.
The image on the left represents the latest and best map of what our own Galaxy looks like, and our place within it [credit: ].
We know quite a lot about our own Galaxy [e.g. see galaxymap.org, but be aware that galaxymap.org shows the images rotated by exactly 180 degrees compared to the new map], but every now and again something interesting and unexpected pops out to surprise us.
For example, we used to think the Milky Way was a four-armed Spiral galaxy with a few straggly sub-arms or spurs (e.g. see here). The main arms in the old picture were the Norma, Scutum-Centaurus, Sagittarius and Perseus arms. Our Sun currently resides in none of these arms but in the Orion spur.
Now new work using the Spitzer Space Telescope by Bob Benjamin and his collaborators (this is a press release) has shown that the Norma and Sagittarius arms do not deserve their status as major arms: instead the Milky Way is a two-armed grand-design spiral (as shown in the image above). Compare the new image (shown above) to a recent but older Milky Way map also from the Spitzer Science Center's web site.
Space.com also as the story.
[Update 06/06/2008: Fixed a typo, noted that the Sun's location in the Orion Spur is only its current location, and added a label]
Posted by Dave Strickland at 9:13 PM