Picture an exploding star. You probably picture a round ball going boom in a round way. But real supernovae apparently aren't like that at all.

Astronomers have realized for a few years now that Type II supernovae — the kind that result from the collapse of a massive supergiant star's core — explode from the inside like a ball suddenly growing a spindle, at least in some cases. Very likely, the tiny collapsing core emits two incredibly powerful jets along its axis of rotation, and these play the major role in blowing the entire rest of the star apart. In extreme cases, the jets power a gamma-ray burst directed along their flight lines after they break out of the star's poles. In lesser cases, the jets may not make it out of the star at all, but still cause the explosion to be asymmetrical. (See "Supernovae Are Not Round" in Sky & Telescope, January 2002, page 40.)

That's a Type II blast. Entirely different are Type Ia supernovae. These get their energy not from gravitational collapse inside a supergiant, but from a tiny white dwarf star that becomes overloaded with mass and explodes via thermonuclear fusion like a big hydrogen bomb (except that it's carbon, not hydrogen, that fuses).

Presumably, the added mass that nudges the white dwarf over its tipping point is gas that's been slowly spilling onto it from a close binary companion star — at least according to the most widely accepted theory.

Now it appears that Type Ia supernovae are not round either.

Nothing about these events is intuitive. The temperatures, densities, sizes, in fact all the physics are so extreme that our earthly habits of imagining things aren't much good. The only way to figure out what happens is to follow the fundamental physics from the ground up.

That's what supercomputers are for. Last Friday, astrophysicists at the University of Chicago announced that they've used a supercomputer to run preliminary 3-D simulations of what happens when an overloaded white dwarf gets too burdened and thermonuclear fusion begins at a spot close to its center. They plan to do more of this modeling work using the Blue Gene/P supercomputer at Argonne National Laboratory.

As it turns out, the white dwarf doesn't detonate as if it were a ball of TNT, with the explosion proceeding in a shock front faster than the speed of sound in the material. Instead, the star deflagrates, at least at first, with a thermonuclear "flame" spreading through the star's interior slower than the local speed of sound. If a detonation goes bang, a deflagration goes whoosh.

And, weirdly, the first whooshed part forms a superhot, low-density bubble that quickly rises from the center (first two pictures above). The bubble bursts through one side of the star in less than a second, so intense is the white dwarf's gravity pulling the rest of the star's dense matter inward.

Then things really get weird. “The fast-moving [thermonuclear] ash stays confined to the surface, flows around the white dwarf and collides on the opposite side of the breakout,” says team member Cal Jordan. There the colliding material finally triggers a detonation, which quickly incinerates the rest of the star with a shock-wave bang. The start of the detonation is shown in the frame at right.

Read the press release, and watch the movies. Enjoy.

NASA's upcoming service call on the Hubble Space Telescope won't happen till late September or early October. Until recently it had been scheduled to begin in late August. Rumors about the slip have been circulating for weeks. They were confirmed yesterday by Space Shuttle program manager John Shannon, as reported in the Houston Chronicle.

As with most other launch delays over the history of the Hubble program, the source of the slip isn't the telescope — it's the shuttle. NASA needs more time to prepare two giant external fuel tanks for the mission, which will be flown on the shuttle Atlantis. Normally only one tank is needed. But if anything goes wrong during ascent, the astronauts won't be able to seek safe haven at the International Space Station, which is in a different orbit than Hubble. So NASA will have a second shuttle on the launch pad, poised to come to Atlantis's rescue if needed.

You probably remember that in 2004 NASA administrator Sean O'Keefe cancelled the upcoming servicing mission. He made the controversial move because of safety concerns after the February 2003 Columbia disaster. When Michael Griffin took over as NASA chief two years later, he reexamined the issue and concluded that servicing Hubble is actually no more risky than visiting the space station — as long as that second-shuttle-on-the-pad rescue option is available.

Why does Hubble need servicing again? After all, it's been repaired and upgraded four times already. Well, space is a harsh and unforgiving environment, with extreme temperature swings, an unending rain of meteoroids and high-energy particles, and other hazards. Hubble has been up there for 18 years now, and some of its critical parts — including the batteries that power its instruments through orbital night — are original equipment. So some amount of refurbishment is needed just to keep the telescope operating.

More important, though, is keeping Hubble at the forefront of scientific discovery. The way to do that is to replace old instruments with new state-of-the-art ones. So not only will Atlantis's astronauts deliver new batteries, gyroscopes, insulation, and other mechanical and electrical components, but they'll also install the Wide Field Camera 3 and the Cosmic Origins Spectrograph. These two new detectors will enhance the telescope's "discovery power" (the product of its areal coverage and sensitivity) by a factor of 100 or so, ensuring that Hubble will continue to reveal new cosmic wonders until — and even after — the larger James Webb Space Telescope goes into orbit around 2013.

You can follow preparations for the Hubble servicing mission at the STS-125 website (in NASA parlance, it's Space Transportation System mission number 125).

Black-hole jets are among the most violent, and important, phenomena in the universe. When matter falls toward a black hole, it often forms an extremely hot "accretion disk" around the hole as it spirals in. Somehow, despite the intense gravity hauling things inward, the inner part of the accretion disk often manages to emit narrow jets of matter from its top and bottom faces. Typically, a few percent of the infalling stuff ends up getting expelled this way, powered somehow by the energy of the rest falling in.

These accretion-disk jets can extend millions of light-years from the cores of active radio galaxies and quasars. We also see them in miniature squirting from "microquasars" in our own galaxy, when enough matter feeds into a stellar-mass black hole.

And in extreme form they almost certainly lie at the root of gamma-ray bursts, where the massive, superdense, fast-spinning core of a supergiant star suddenly collapses into a black hole.

But how do they work? This used to be one of the biggest mysteries in astrophysics. In recent years, however, physicists have been pretty sure they've gotten it figured out. This is the scenario:

The spinning accretion disk develops an intensely powerful magnetic field. (Because the gas is very hot, electrons get stripped off atoms and can move around freely, so the gas is electrically conducting — a plasma — a lot like the copper conductors in a spinning generator.) The disk's spin wraps up the magnetic field into a tight spiral; the most intense, tightly wound part of the field breaks loose and squirts upward from the disk's inner poles; and plasma (because it's tied to magnetic fields, just like any moving conductor is) flies out along with it.

That's the theory. A lot of indirect evidence from active galactic nuclei has supported various parts of it. But now astronomers have found a really good smoking gun.

The object they studied is known as BL Lacertae, so named because it was originally mistaken for a variable star. BL Lac is a blazar: a quasar that happens to be oriented so that we look right down into its jet. Think of a truly stupendous monster opening its throat at us, saying "Aaah," and gushing high-energy vomit — as we observe from a safe distance. In this case, the distance is 950 million light-years.

Using a combination of X-ray, visible-light, and high-resolution radio observations, the group got an excellent look at a blob of plasma getting coughed up right from the bottom of the inner throat. They watched the material winding its way around a corkscrew-shaped path outward, exactly as predicted by the spiral-magnetic-field theory.

"We have gotten the clearest look yet at the innermost portion of the jet, where the stream of particles is actually accelerated, and everything we see supports the idea that twisted, coiled magnetic fields are propelling the material," says Alan Marscher of Boston University, leader of the research team. "This is a major advance in our understanding of a remarkable process that occurs throughout the universe."

For more about this, see the group's press release site, which includes a movie of their model of BL Lacertae in action. (The site also links to Marscher with guitar performing his ode to BL Lac, "Superluminal Lover".) Their paper appears in the April 24, 2008, issue of Nature.

Despite its name, the Northeast Astronomy Forum (NEAF) is primarily a trade show where makers and vendors of astronomical equipment show off their products.

In general, I'm not much of a gearhead. I attend NEAF mostly to shoot the breeze with observers from all over the country, and the booths that interest me most are the ones advertising astronomy clubs and planetariums. But every now and then a piece of equipment catches my eye for one reason or another.

This year, I was most interested in the display by Mag 1 Instruments, makers of the legendary Portaball telescope. I was surprised to see the booth, since I knew that Peter Smitka, the former owner, had decided to go out of business. But it turns out that Smitka has sold Mag 1 to David Juckem, an avid amateur astronomer whose day job is machining precision parts for military and medical applications. Sounds like a match made in heaven!

Often described as an Astroscan on steroids, the Portaball is unlike any other telescope on the market. Like a Dob, it's steered by human brainpower, driven by muscle power, and controlled by friction. But in place of a Dob's low-tech wooden construction, the Portaball is all gleaming metal and (where appropriate) plastic.

More to the point, the Portaball doesn't have vertical and horizontal axes; the tube is free to turn in every direction. That has two huge advantages. First, it eliminates the notorious "Dobsonian hole." Tracking through the zenith with a Portaball is just like moving through any other piece of sky. And if the eyepiece seems a little to high or low for comfort, you just rotate the tube to bring the eyepiece to your eye. It's a dream for sharing views at star parties with children and adults alike.

In addition, the old Portaballs have superb optical and mechanical quality. Judging by Juckem's descriptions, the new ones should be better still. I won't know that until I've seen one at work under a starry sky. But I certainly wish Juckem all the best with his new enterprise.

More than 1,000 amateur astronomers performed an annual rite of spring last weekend by flocking to Suffern, New York, to attend the Northeast Astronomy Forum and Telescope Show (NEAF).

Cosponsored by the Rockland Astronomy Club and Sky & Telescope, NEAF has become a "must-see" for telescope enthusiasts. With more than 100 equipment vendors and manufacturers showcasing their wares, it was tough to see everything! And at any given time, attendees could also listen to one of three talks that catered to every level of interest.

This year's lectures highlighted the growing role of women in astronomy. Astronaut Dorothy Metcalf-Lindenburger gave a presentation about the inspiration she experienced as a child that continues to fuel her passion for the stars to this day.

Neta Bahcall of Princeton University discussed the latest thinking about dark matter throughout the universe, while noted observer Barbara Wilson of the George Observatory in Houston presented new insights into the life and work of Caroline Herschel.

Back on the showroom floor, the weekend was kicked off by Al Nagler of Tele Vue Optics, who unveiled his latest creation: the 8-mm Ethos eyepiece, featuring the same ultrawide view of its 13-mm sibling but with more magnification. I can't wait to look through that one under the stars!

Lots of new gear made its debut at the show. On the imaging front, SBIG gave us a look at its upcoming STX camera series, as well as a new standalone autoguider targeting the digital SLR user. Finger Lakes Instrumentation showcased its new Microline series of CCD cameras featuring detectors to fit any imager's budget. The ML89300 looks particularly attractive for users of mid-range telescopes. Quantum Scientific Imaging also rolled out its new QSI 532wsg camera with integrated off-axis guiding port.

Quite a few new telescopes caught my eye there too. PlaneWave Instruments showed off new 12- and 17-inch versions of its corrected Dall-Kirkham design for deep-sky imagers. A new player in the field, Deep Sky Instruments released a new series of affordable Ritchey-Chrétien telescopes ($4,995 for the 10-inch model).

Speaking of affordable RCs, Astro-Tech displayed a prototype of Chinese manufactured instrument with a base price of $2,995 for an 8-inch tube assembly.

Refractors were well represented at NEAF also, with Stellarvue drawing quite a crowd with its new SV160 apochromatic triplet refractor ($8,990).

For the solar aficionado, Lunt Solar Systems showed off its LST60T/Ha hydrogen-alpha (Hα) scopes, as well as an 8-inch dual-bandpass (Hα and calcium-K) model. DayStar Filters had its new Quantum Series filters, as well as its new Solar REDi dedicated imaging telescope system. Too bad the sky didn't cooperate that well for these scopes out in the courtyard — we got brief glimpses of the Sun only on Saturday.

Among software developers, Software Bisque introduced TheSkyX that will run on both Windows and Mac platforms, while Diffraction Limited revealed MaxIm DL5 geared to handle the biggest CCD image processing needs. CCDWare displayed the newest iterations of both CCDAutopilot and CCDInspector.

There was just too much to report here! But much more will be featured in our expanded coverage, coming in the August issue of Sky & Telescope.

Polaris is important not just because it's the North Star. It also happens to be the brightest and nearest Cepheid variable star, 430 light-years away. Cepheids, a special class of pulsating giants, have provided astronomers with a crucial link in the cosmic distance scale for almost a century. But Polaris isn't just any Cepheid. It has been changing its period and especially the amplitude of its pulsations.

Polaris varies in brightness only slightly, by just a few percent across its 3.97-day cycle. Moreover, the pulsations steadily diminished for decades: from 0.12 magnitude per cycle a century ago — almost enough to see by eye — to a mere 0.02 magnitude per cycle in the mid-1990s. Astronomers wondered if Polaris was about to stop pulsing completely.

Apparently not. Four years ago Edward F. Guinan (Villanova University) and several colleagues reported that Polaris's fluctuations bottomed out in the mid-1990s and had started increasing again, to 0.038 magnitude per cycle in 2004. Now an international team of nine astronomers finds the trend continuing. From 2003 to 2007, says the team, Polaris's brightness pulsations increased by an additional one-third.

The group used instuments aboard satellites to monitor Polaris almost continuously for 4.5 years. Based in this very high-quality data, they suggest that Polaris is not evolving away from the "instability strip" due to long-term, one-way stellar evolution as astrophysicists thought, but instead is showing some kind of centuries-long, periodic behavior and no evolution at all.

So the mysteries of the North Star continue. The group's paper will appear in the Astrophysical Journal.. You can read it as a preprint on the Astro-ph preprint server, which has been taking over from traditional journals as the main place where astronomy researchers share their news.

The Northeast Astro-Imaging Conference (NEAIC) kicked off Thursday here in Suffern, New York., featuring talks by many of the biggest names in astrophotography. At any given time during NEAIC there are three events held simultaneously. Needless to say, I've had to make some tough choices!

Yesterday I watched Ken Crawford give an inspiring presentation on achieving depth in your astro-images using advanced techniques in Adobe Photoshop. Ken's work never ceases to amaze me!

Later in the afternoon, I gained new appreciation for the nuances of giant-telescope design by listening to renowned optical designer and astrophotographer Peter Ceravolo. In a riveting session, he described his experience with huge field flatteners and CCD cameras.

I also heard R. Jay GaBany present his remarkable work collaborating with professional astronomers. Jay combines cutting-edge science with aesthetic imaging. If you ever get the opportunity to see Jay speak, don't miss it! You'll never look at your images the same way again.

Another one of the added bonuses of NEAIC is that attendees get a first look at new products from many of the major manufacturers and distributors such as Apogee, Finger Lakes, QSI, Software Bisque, and others. Some highlights include SBIG unveiling the upcoming large-format STX camera series that will not only feature big CCD detectors, but also new revolutionary guiding capabilities. Adirondack showed off its new Fireball Cam that will automatically record and save images of meteors, sprites, and other upper-atmosphere phenomena.

Do you remember what you were doing 18 years ago today? I was sitting in the press auditorium at NASA's Goddard Space Flight Center in Greenbelt, Maryland, watching a large video display showing astronauts aboard the Space Shuttle Discovery working to deploy the Hubble Space Telescope. With more than 20 years of effort and more than $1.5 billion invested in the project, the stakes were high indeed.


Discovery's launch the previous day had gone off without a hitch, but this day things weren't going so well. Crew members Bruce McCandless and Kathryn Sullivan were in the shuttle's airlock, wearing spacesuits and preparing to head outside to give Hubble a helping hand. The telescope's huge solar-cell wings weren't unfurling properly — they were stuck partway out and threatening to tear.

Flight controllers were eventually able to remotely adjust the tension in the deployment mechanism and slowly inch the solar arrays to their full extension, so McCandless and Sullivan avoided an emergency spacewalk. Soon astronomer-astronaut Steven Hawley, at the controls of the shuttle's robotic arm, released his grip on Hubble and sent the telescope on its way as astronomers the world over cheered it on.

Barely two months later, astronomers were plunged into the depths of despair. Early images revealed that Hubble's vision was blurred by spherical aberration, an optical defect that's common in cheap telescopes but inexcusible in one costing billions. Rather than fulfilling astronomers' dreams, Hubble was a nightmare — the butt of jokes on late-night television and a terrible embarrassment for anyone with any connection to astronomy.

Yet, as everyone knows, NASA and its partner, the European Space Agency, refused to give up on Hubble. The agencies' best scientists and engineers came up with a plan to counteract the flawed optics, and in December 1993 astronauts aboard the shuttle Endeavour made Hubble right. Over the next 15 years, by enabling landmark discoveries from our solar system to the edge of the visible universe, the telescope has become widely acknowledged as perhaps the most successful scientific instrument of all time.

On this 18th anniversary of Hubble's deployment, NASA is preparing for the last of its scheduled service calls to the telescope. On shuttle mission STS 125, the only remaining flight not going to the International Space Station, seven astronauts will rendezvous with Hubble to install new scientific instruments, replace worn-out mechanical and electrical parts, add new insulation blankets, and raise the spacecraft's orbit. Launch is officially scheduled for August 28th, but word within the project is that it'll slip at least a little, perhaps to mid-September.

If all goes well during this year's servicing mission, Hubble should be able to remain scientifically productive for another 5 years or more. In fact, because of the improved sensitivity of its new detectors, it should be able to "push the envelope" of cosmic discovery even more aggressively than it has over the last 15 years.

So, happy birthday, Hubble — and many more!

This weekend make plans to attend the largest annual astronomy trade show in America, at the Rockland Community College campus in Suffern, New York — the Northeast Astronomy Forum & Telescope Show (NEAF). Sponsored by the Rockland Astronomy Club and Sky & Telescope, NEAF features the latest telescopes and accessories from more than 100 vendors. It also showcases talks by leading amateur and professional astronomers, and workshops geared toward all levels of hobbyist, from beginner to advanced.

Some of this year's marquee speakers include astronaut Dorothy Metcalf-Lindenburger, planetary scientist Heidi Hammel (Space Science Institute), and astronomer Neta Bahcall. Many activities will be available for families, including solar observing and evening telescope demonstrations.

As a final note, this morning hundreds of astrophotographers kicked off the Northeast Astro Imaging Conference. The sold-out event features lectures from some of the biggest names in astroimaging. I'm here in the crowd, so keep an eye on this site for highlights from some of the presentations.

Ever since Halton Arp's Atlas of Pecular Galaxies (1966) and B. A. Vorontsov-Velaminov's Catalogue of Interacting Galaxies (1959 and 1976), astronomers and the public have been fascinated by these biggest cosmic smashups.

One reason is because there are a lot of them. Unlike most astronomical objects, galaxies are fairly large compared to the distances between them. So every now and then they run into each other — unlike stars or planets, which are very tiny compared to their separations.

Nowadays we know that galaxy collisions are more than just interesting flukes. They have been critical to the history of galaxy evolution and star formation throughout the universe. Big galaxies like the Milky Way got built up by collisions and mergers of little ones, which were the first to develop from the Big Bang. A collision disrupts and compresses the interstellar gas clouds in each galaxy involved, and this caused the huge bursts of star formation that lit the early universe. (Younger stars like our Sun are in the minority of latecomers.) The complete piecing together of cosmic-structure formation, from the Big Bang to now, has been one of the triumphs of modern cosmology — and it has put galaxy collisions front-and-center.

This morning the Hubble Heritage Project, the team in charge of compiling beautiful Hubble pictures for the public, released a collection of 59 greatest galaxy hits — literally. The images sample the huge range of forms that result from various types of galaxy interactions in the modern-day universe. Here's the team's press release, and here are the high-resolution images.

"Most of the 59 new Hubble images are part of a large investigation of luminous and ultraluminous infrared galaxies called the GOALS project (Great Observatories All-sky LIRG Survey)," says the group. The GOALS survey combines observations from Hubble (which sees visible and near-infrared light); the Spitzer Space Observatory (mid-and far-infrared), the Galaxy Explorer or GALEX (ultraviolet), and the Chandra X-Ray Observatory.

Large-scale violence, small-scale peace

It's no coincidence that a survey of infrared-bright galaxies would pick up a lot of colliders. Collisions cause gas-cloud compression and bursts of star formation; the swarms of massive young stars blaze brilliantly and shed massive amounts of dust; the dust absorbs the brilliant light and re-emits it as infrared radiation; the infrared gets out through the dust for our instruments to see.

For all the drama, however, creatures living on a planet in a colliding galaxy would experience few effects other than a very interesting night sky. The galaxies' individual stars are too far apart to collide (or even disrupt each others' planetary systems, by and large). And though a pass through a brilliant star-forming region might give your upper atmosphere some high-energy heebie-jeebies, such events can't be too bad, or we couldn't have evolved here on Earth. Our Milky Way contains many identifiable star streams that are the last traces of small galaxies that collided with and merged into ours in relatively recent cosmic times.

We live in the golden age of sky surveys. These are projects that, rather than studying a particular astronomical object, inventory a large area of sky for everything within it that meets some particular set of criteria.

The grandaddy of all such projects is the National Geographic Society – Palomar Observatory Sky Survey (POSS), created from 1950 to 1957. It photographed all of the available celestial sphere to about 22nd magnitude in red and blue light on 14-inch-square glass plates, using the Palomar 48-inch Schmidt camera. The revolutionary effects of POSS (and its extensions) throughout astronomy proved the huge value of such projects, and POSS laid the way for many other kinds of surveys to follow.

A second revolution came with digital imagers, image-analysis software, and automatic database creation — so that today's surveys (often available as images online) contain countless objects that have never been studied or even been looked at by a human eye. "Data mining" has thus become an important new branch of research astronomy: no telescope required.

All this is by way of background to a press release that we got a few days ago from the European Southern Observatory (ESO). It announces that the 4.1-meter (160-inch) mirror has been completed for the upcoming VISTA project, the Visible and Infrared Survey Telescope for Astronomy. This project will map the southern sky with new depth and resolution in the near infrared, with especial value for studies of solar systems being born, low-mass brown dwarfs, and cosmology involving highly redshifted objects in the early universe.

The mirror itself, with a deep f/1 hyperboloid shape, is the most steeply curved optic of its size ever made. The telescope is under construction at ESO's Cerro Paranal site in the Chilean Andes. It should be finished, fine-tuned, and starting work by early next year.

No one paid attention outside a few circles of astronomers. So far, the press release has failed to prompt any news article caught by Google News. But in coming years VISTA, like other new giant surveys now in the works, will surely affect everyone's view of the universe.

It's been 40 years since space physicists realized that cyclic throbbings they'd seen on the Sun's visible surface were caused by periodic pressure waves — literally sounds — reverberating through the solar interior. The discovery created a new scientific discipline: helioseismology.

You won't hear this ringing in your ears if you listen closely on a sunny day. For one thing, the sound waves are trapped inside the Sun and can't propagate out into space. And the "loudest" frequencies cluster around 0.003 hertz, or one vibration every 5 minutes. That's more than 12 octaves below the lowest notes we humans can hear.

The Sun isn't so much singing as it is humming constantly, the kind of ostinato you'd get from a bell hung out in the desert that constantly being pelted with sand grains.

But a new study, to appear in the May 1st edition of Astrophysical Journal Letters, reports that ol' Sol is coaxed into throaty solos whenever a solar flare erupts. Christoffer Karoff and Hans Kjeldsen, both at the University of Aarhus in Denmark, chanced upon this connection as they analyzed data from the workhorse Solar and Heliospheric Observatory, a spacecraft launched jointly by the European Space Agency and NASA in 1995.

“The signal we saw was like someone occasionally walking up to the bell and striking it, which told us that there was something missing from our understanding of how the Sun works,” Karoff notes in an ESA press release.

As a second ESA press release points out, researchers have suspected for decades that flares beget sunquakes. The new SOHO findings confirm that when solar-flare counts go up, so does the strength of the 5-minute oscillations. It's a situation akin to the weeks of ringing that geophysicists observe deep in our planet's interior after a strong earthquake.

The Sun's rippling surface is evident in a captivating SOHO video just released by ESA. The 56-second-long clip shows the Sun's activity over several days in 2003 and a titanic flare (a few seconds from the end) that erupted on November 4th.

But the correlation between the flares and sunquakes is ironclad in data returned from a SOHO instrument called VIRGO, short for Variability of solar IRradiance and Gravity Oscillations. You can see this for yourself in a special report on NASA's SOHO webpage.

Karoff and Kjeldsen don't yet understand why flares trigger the enhanced oscillations. They're working on that now. And they're also looking for similar tunes from other stars — both with sensitive ground-based instruments and with the ESA's COROT spacecraft.

Google Inc. released a new version of Google Earth this week (Version 4.3 Beta) that, of course, has some new features.

It will now display sunlight, so that you can see the dark and illuminated portions of the Earth, as well as make cool vistas when you turn on the 3-D buildings. But the most time-wasting aspect is that it now incorporates the Street View capability from Google Maps — and the images are more detailed. I can almost see in the windows of my house.

On the Google Sky front, telescope-maker Celestron announced yesterday that they will be providing audio clips from their SkyScout Audio Tours. After invoking Sky mode with the Saturn icon, you'll find tours in the Layers menu under Sky Database > Education Center. Currently, the audio clips are very brief identifications of constellations. More to come soon, I presume!

Also new in the Education Center is the Virtual Tourism layer, which is fun to browse. It has a smattering of astronomy related YouTube videos.

It's of no consequence, but the Pioneer 10 spacecraft launched on my 9th birthday. Although I don't recall if I noted the event while in the 3rd grade, that was the year I remember becoming interested in astronomy. That year I did a big report on "space" with my then best friend. (I still wonder if there are any remnants of the spray paint we used on the schoolyard blacktop to create our impressive outer-space backdrop for our model solar system.)

During the following 3½ decades, Pioneer 10 and its twin, Pioneer 11, blazed a trail out to Jupiter and Saturn, and then continued onward, well beyond the orbit of Pluto. They eventually fell silent — Pioneer 11 faded out in 1995 and Pioneer 10 lasted until 2003.

But during the mission's many years of operation, tracking specialists noticed something odd: neither craft was exactly where it was supposed to be. After crossing billions of miles in space, they were instead thousands of miles closer to the Sun than expected — a tiny fraction of the distance traveled, but nevertheless significant. Significant enough to have some people wondering if it was a sign of some unknown refinement needed to the theory of gravity, a bedrock of modern physics.

The latest examination of this curiosity concludes that no exotic explanations are required. According to Slava Turyshev (Jet Propulsion Laboratory), some of the retarding force is due to uneven emission of heat radiation from the spacecraft. He described his preliminary findings at a meeting of the American Physical Society earlier in the week, summing up work he's been doing for 15 years.

Turyshev has spent the last several years retrieving archival tracking records from obsolete storage media (those classic magnetic tapes, some of them corrupted) as well as detailed specifications of the Pioneer spacecraft itself from 40 years ago. He likens his searching and discovery to rooting around a dusty attic. "No one told me what I'd be getting into," he says. The Pioneer missions lasted so long that they outlived programming languages and data formats. (The Pioneers were launched in the days of punched cards.)

After piecing together the tracking history, Turyshev and his colleagues created a computer model of the Pioneer spacecraft and determined that they had warm and cool spots not previously modeled well. The uneven emission of infrared photons from the craft's radioactive power sources could account for at least a third of Pioneer 11's anomalous acceleration. (Photons, like other particles, carry a bit of momentum.)

What's still unclear is how the warm surfaces may have physically changed during the decades in space. Space weathering by dust particles, solar wind, and ultraviolet sunlight could have altered the thermal properties of the surfaces significantly, possibly enhancing the effect enough to account for the entire "Pioneer anomaly." The researchers hope to get clues to this by running various computer simulations of their model and by examining 40 gigabytes of telemetry data, which will indicate the state of many systems on the spacecraft, and thus how much power they actually used and how much heat they gave off.

At some point you've probably been driving down the freeway when a bug splats itself on your windshield. Did the impact send you careening off the side of the road? I thought not. But that's the underlying premise of a ridiculous story that took the Internet by storm yesterday.

It seems that a 13-year-old German student chose a study of near-Earth asteroids for his entry in a prestigious science-fair competition. While crunching the numbers for a 1,000-foot-wide asteroid named 99942 Apophis, he discovered that the giant rock might strike an orbiting satellite when it brushes within 18,000 to 20,000 miles of Earth on April 13, 2029.

That possibility, the student concluded, had been overlooked by NASA's top dynamicists, and it increased the chance of Apophis crashing into Earth itself on a subsequent pass in 2036 from 1 in 45,000 (NASA's estimate) to just 1 in 450. It's a harrowing prospect — if he had actually been correct.

The story first appeared on April 4th in Bild, the German equivalent of Weekly World News. "I have calculated the end of the world!" screams the headline "...and NASA says, I'm right." This silliness might have died quietly, had the Agence France-Presse not repeated and embellished the tale on April 15th.

Kudos to German science writer Daniel Fischer, who got to the bottom of this mess and yesterday exposed it for the farce (or hoax) it was.

First, the boy misunderstood the flyby geometry in 2029 — the chance of striking a satellite is "vanishingly unlikely," NASA scientists insist. While it's true that Apophis will pass closer than the altitude of geosynchronous satellites, it'll be well outside them when it crosses Earth's equatorial plane, where they're located.

Second, Apophis has an estimated mass of some 20 million tons. Even if it did have a head-on collision with a sizable satellite, the impact would barely affect the asteroid's trajectory. (If you don't believe me, just ask the bug.)