Some amateur astronomers can't live without their Clear Sky Chart, the handy graphic that forecasts such need-to-know atmospheric conditions like cloud cover, transparency, and humidity. The major problem with Attilla Danko's fabulous service is that it's only available for North America — most of it, anyway.

We received word this morning that now the rest of the world can benefit from a similar website built by Chinese programmer Ye Quanzhi. His Astroweather Panel covers everywhere Clear Sky Chart does not. Select a location by entering your geographic coordinates, or navigate through the place names, organized by country, already in the system.

Check it out and please post a comment below with your experiences.

OK, I’ll admit it: With so NASA many missions under way right now, it’s hard to keep track of what they’re all up to. That’s why it was a little surprising to learn this week of an intriguing new result from a scientific spacecraft that’s been off my radar screen for some time.

The Reuven Ramaty High-Energy Solar Spectroscopic Imager &mdash called RHESSI, though it was just HESSI before being renamed to honor a pioneering solar physicist — rocketed into space on February 5, 2002. Since then it’s been scrutinizing the Sun’s face with X- and gamma-ray imagers, primarily to probe how energy is released and propagates during solar flares.

Apparently RHESSI has been moonlighting as a solar yardstick, measuring the Sun’s dimensions with unprecedented accuracy. Our star’s spin rate, once every 25.3 days at the equator, causes its midsection to bulge outward ever so slightly relative to its poles. The predicted value of this oblateness is 7.8 milli-arcseconds, about the apparent size of a dime in Boston as seen from San Francisco. It’s only about 0.0001% of the Sun’s diameter — not the sort of deviation that’s easy to detect, let alone measure.

Yet in this week’s Science Express, where Science trumpets articles before they appear in print, a quartet of researchers led by Martin Fivian (University of California, Berkeley) announced that the Sun is a little more oblate than predicted, a hair more than 8 milli-arcseconds. Moreover, when the team combined RHESSI’s measurements with those acquired previously, it found that the polar flattening becomes even more pronounced, by another 10.8 milli-arcseconds, during times of high solar activity.

These results might seem trivial, but solar physicists assure us they are not. The changing girth arises in magnetic ridges on the Sun’s surface that mimic, subtly, the texture of a cantaloupe’s skin. The deviation from a perfect sphere has implications for how the Sun pulls on Mercury, how the solar core is shaped, and perhaps how acoustic waves propagate throughout the solar interior.

Fortunately, the variable oblateness is far too inconsequential to affect predictions for the durations of solar eclipses — except for the most ardent purists. As diehard “umbraphile” Glenn Schneider points out, eclipse calculations usually consider the shape of the solar and lunar disks only to a precision of about 1 arcsecond, 50 to 100 times greater than what RHESSI measured.

If NASA had kept to its original schedule, astronauts would have made their fifth and final mission to service the Hubble Space Telescope back in August.

It's a good thing they didn't.

The space agency announced today that an onboard communication problem has temporarily shut down the World's Greatest Telescope — and postponed the planned house call in orbit, scheduled to begin October 14th, until no earlier than next February or perhaps April.

The failure occurred in the Command Unit Science Data Formatter, an electronics package that moves digitized streams of data from the science instruments to spacecraft's digital tape recorder for later playback to Earth. The CU/SDF has worked great for 18 years, so faulty craftsmanship isn't the issue. Nor is the venerable space observatory in any real trouble.

The good news is the that Hubble's designers included a second unit for redundancy. As far as engineers know, it still works — but it hasn't been checked since before HST's launch more than 18 years ago. Changing from one to the other is entirely doable but a lot more involved than just throwing a switch from "A" to "B". So Hubble's handlers are dusting off the owner's manual to begin the process; that might be completed by early next week, at which point the observatory will come back online.

More weighty, for the moment, is whether replacing the defective unit should be added to the already jam-packed "to do" list for astronauts on the forthcoming servicing mission, STS 125. A spare CU/SDF does exist at NASA's Goddard Space Flight Center (which manages Hubble's science payload) and could be made flight-ready soon.

During a hastily convened briefing for reporters today, Preston Burch, Hubble manager at NASA-Goddard, noted that replacing the 136-pound unit, which is roughly the size of a two-drawer filing cabinet, should be "a relatively straightforward activity" that would add only about 2 hours to one of the mission's five planned spacewalks.

It'll take a few months to certify that the spare is flightworthy, but NASA officials seem willing to accept that delay. This means the Space Shuttle Atlantis, already on the launch pad at the Kennedy Space Center in Florida, will be rolled back into its shelter. So will a second shuttle, Endeavour, that's standing by just in case a dramatic rescue of the Hubble repair team had been necessary.

As detailed in Sky & Telescope's October issue, the STS-125 crew hopes to install two scientific instruments (the Cosmic Origins Spectrograph and a replacement Advanced Camera for Surveys), repair a third, and swap in new batteries, gyroscopes, and other components. The spacewalkers will also attach a mechanism to allow the docking of a rocket stage at some future date for Hubble's safe disposal.

Should the replacement data formatter prove unfit to fly (considered unlikely), the repair mission will be hustled back to the launch pad as soon as it can — probably in November.

"Hubble has a habit of coming back from adversity," notes Edward Weiler, who heads NASA's Science Mission Directorate. "This particular failure was anticipated 20 years ago, and we have spare hardware ready to go."

I've always had a soft spot for an interplanetary pioneer called Ulysses. Built by the European Space Agency, it was launched in 1990 toward Jupiter, where the planet's powerful gravity yanked the craft out of the ecliptic plane and onto a looping path that carries it over and under the Sun every six years.

The initial mission concept, known as the International Solar Polar Mission, called for two identical craft — one European and one American — to study high-latitude regions of the Sun that can't be studied from Earth. But NASA reneged on its end of the deal, so Ulysses has soldiered on alone.

Recently it completed its third and final pass over the Sun's poles. That kind of longevity, far exceeding the planned 5-year-long mission, has really paid off. Ulysses's observations show that the solar wind is particularly feeble right now, with just 75% the strength it had a decade ago. In fact it's never been this weak since monitoring began a half century ago.

Space physicists had expected the flow to tail off, because the Sun's 11-year activity cycle is now at a minimum. But it's got far less punch than that seen during the last minimum. "The wind speed is almost the same, but the density and pressure are significantly lower," notes investigator David McComas (Southwest Research Institute), whose SWOOPS instrument aboard Ulysses has been key to the new finding.

The solar wind consists of plasma (ionized matter) and entrained solar magnetic field lines that pushed outward from the Sun's atmosphere into interplanetary space. Ulysses had previously shown that the wind comes off the Sun's poles faster and with less turbulence than it does from its midsection. But both the polar and equatorial flows have throttled back to historic lows.

There'd been earlier hints, in deep-space observations from IMP 8 and Voyager 2, that the solar wind variously ebbed and flowed during a solar cycle. Still, McComas and his colleagues, who detail their results in the September 18th issue of Geophysical Research Letters, don't know why the solar wind is taking a breather. One suspicion: perhaps the outflow is somehow being energized higher up in the Sun's corona, where there's less mass available to push outward into space.

In any case, the low flow means that the gigantic electromagnetic bubble that surrounds the Sun and planets must be shrinking inward and, with it, the solar system's boundary with interstellar space (called the heliopause). Both Voyager spacecraft are nearing this threshhold; they've aleady encountered a shock front inside the heliopause, and if this weak solar wind keeps up, Voyager 1 may find itself popping outside the heliosphere years sooner than expected.

Meanwhile, Ulysses itself is nearing the end of its historic mission. FLight controllers have been keeping a death watch all year, because the craft's source of heat and power (radioactive plutonium) has dwindled so much that the fuel lines are in imminent danger of freezing.

I contacted ESA project manager Richard Marsden for an update on the craft's health. "True to its name, Ulysses refuses to give up without a fight," he replied. "We're still getting science data, albeit only a few hours per day." The team has kept the fuel from freezing by firing thrusters every two hours. But the fuel is running low, and the team expects Ulysses to run dry sometime between the end of September and December. "With a bit of luck," Marsden adds, "we'll encounter the slow solar wind once again before then."

Hang in there, Ulysses!

Someone once said, "Opportunity knocks only once, but temptation bangs on your door for years." And ever since NASA plopped twin rovers onto the ruddy surface of Mars in early 2004, mission scientists have exploited the longevity of their mechanical marvels to explore ever-wider swaths of Martian real estate.

The rover Opportunity, in particular, recently wrapped up an entire year of scientific prospecting along the rocky inner slopes of Victoria crater — after rolling 4 miles (6 km) to get there. Measuring 2,400 feet across and about a tenth as deep, Victoria provided a ready-made "road cut" in the upper crust that allowed geologists to peer back into recent Martian history.

Now rover-meister Steven Squyres wants to dispatch Opportunity on an even more audacious undertaking: a 7-mile (12-km) trek to an even larger crater named Endeavour. It's about as far away as the entire distance that the rover has traveled to date, and the craft is already well past its 90-day warranty.

But reaching (or even nearing) 14-mile-wide Endeavour would provide a scientific boon, since the impact that created it undoubtedly unearthed countless rocks from deep crustal layers and lobbed them onto the surrounding terrain. Squyres also points out that heading south, toward that big pit, is where Opportunity would be heading next anyway.

The craft is in excellent shape, though there's a balky motor in the shoulder joint of its instrument-tipped robotic arm. And it'll have two advantages that should make the going easier. One is the eagle-eyed Mars Reconnaissance Orbiter, whose High Resolution Imaging Science Experiment (HiRISE) camera can record surface details smaller than the rover itself. The other is new onboard programming that helps the both rovers optimize their routes to avoid hazards such as sand dunes.

Still, Opportunity will have to hustle to reach Endeavour. Even clipping along at 110 yards per day, engineers estimate that the journey could take two years.

By the way, NASA's exploration of Mars was featured last week on National Public Radio's "Talk of the Nation: Science Friday." If you missed the broadcast, you can listen to streamed audio here.

On September 17th, the International Astronomical Union announced that an object in the Kuiper Belt — the fifth solar-system body large enough to qualify as a "dwarf planet" — had been named. It'll be called Haumea (pronounced how-MAY-uh), after the goddess of childbirth and fertility in Hawaiian mythology.

But there's far more to the story. When it comes to naming Kuiper Belt objects, the IAU typically accommodates whatever's suggested by the discoverer(s). In the case of Haumea, formerly designated 2003 EL₆₁ and now formally numbered minor planet 136108, there's debate — controversy, actually — over who discovered it.

Haumea is the name suggested by Michael Brown (Caltech), who together with Chad Trujillo and David Rabinowitz spotted it on December 28, 2004. But Brown didn't report his team's observations right away to the IAU's clearinghouse for such discoveries, the Minor Planet Center in Cambridge, Massachusetts, as he explains on his website. Instead, he and others continued to scrutinize this relatively bright and thus sizable body — learning a month later, for example, that it had a moon. (They eventually found a second moon as well.)

In July 2005, just as Brown was preparing to announce all this, Spanish astronomers Pablo Santos-Sanz and José Luis Ortiz Moreno sent the MPC some observations of the same object taken two years earlier at little-known Sierra Nevada Observatory. What's become clear since then is that the Spaniards accessed the American team's publicly accessible observing records 39 hours before submitting their discovery claim to the MPC but, they insist, after deducing the existence of 2003 EL₆₁ themselves.

To recap: Brown's team chanced upon the object first, but the Spanish observers reported its discovery first. There's still bad blood over this, and it's not likely to be resolved soon. For now, the MPC's record for asteroid 136108 lists "Sierra Nevada" as both the discoverer(s) and the discovery site, though those details are omitted from Haumea's official naming citation. But you won't find the discoverers' names listed next to Sierra Nevada (which is apparently how the Spaniards wanted it).

So why didn't 2003 EL₆₁ get christened Ataecina, the name suggested by Ortiz and his colleagues? Ataecina was a goddess worshiped by ancient inhabitants of the Iberian peninsula, and she was usually associated to Proserpina, Roman goddess of the underworld. Therein lies the problem: by IAU convention, deities of the underworld are reserved for objects in Pluto-like orbits (in resonance with Neptune), which 2003 EL₆₁ is not.

Brown's team proposed not only Haumea but also Hi'iaka and Namaka (two of Haumea's many children) for the two moons. It all fits together nicely.

But there's been plenty of behind-the-scenes rancor about how these names gained approval. Two groups, the Working Group for Planetary System Nomenclature and the Committee for Small-Body Nomenclature, were under pressure from IAU general secretary General Secretary Karel van der Hucht to resolve the 2003 EL₆₁ naming issue quickly. However, the CSBN's vote on Haumea ended in a tie or at best a slim majority, depending on who's doing the tallying (some of its members sit on the WGPSN as well).

Since the IAU wasn't bound to accept the name proposed by either team, one wonders why the WGPSN and CSBN didn't work harder to come up with something more politically neutral.

Oh, by the way, here's a question for any CSBN or WGPSN members who happen to read this: Is Ceres a dwarf planet? I know that was the IAU's intention when the controversial Pluto votes were cast back in 2006 — but unless I'm missing something, the approved resolutions never mention Ceres.

Discovering a planet around another star is no big deal these days — dozens of them have been reported in 2008 alone, and the total count now stands at more than 300.

Of course, the burgeoning exoplanet population hasn't stopped astronomers from looking for more of them. Big gaps remain in the sampling statistics, because the most successful techniques (radial-velocity monitoring, microlensing events, and periodic transits) favor finding large bodies close to their parent stars. Far-out planets are rarely discovered this way because they have long orbital periods and even longer odds of crossing directly in front of their stars.

But it should be possible to spot alien worlds directly by imaging very young nearby stars. This game plan assumes that any outlying gas-giant planets are still glowing warmly from having formed so recently, making them relatively easy pickings at infrared wavelengths. One of these came to light in 2004, though it orbits a feebly glowing brown dwarf rather than a proper star.

Now a trio of astronomers from the University of Toronto has found a "planetary-mass candidate" next to a young star that has roughly the Sun's mass. To see it, last April they utilized an adaptive-optics-aided infrared imager attached to the Gemini North telescope atop Mauna Kea in Hawaii.

The press release announcing the discovery touts the "First Picture of Likely Planet," but astronomers David Lafrenière, Ray Jayawardhana, and Marten van Kerkwijk are stopping short of calling it that.

For one thing, there's no information yet on the characteristics of its orbit — or, indeed, whether it's even bound to the star at all. They do know that it's not a star, because it's not very hot (about 1,800 kelvins, or 2,700°F) and its infrared spectrum reveals the presence of water and carbon monoxide. Most likely it's about 8 times the mass of Jupiter.

The parent star, which has the snappy designation 1RXS J160929.1-210524, lies about 500 light-years from Earth. So the putative planet's apparent separation of 2.2 arcseconds corresponds to about 330 astronomical units. That's already raised eyebrows among solar-system modelers, because it's highly unlikely that so massive a planet could have formed so far from its star.

The observing team has looked at more than 80 other stars in a 5-million-year-old grouping called the Upper Scorpius Association, and this is the only candidate planet they've turned up to date.

Jayawardhana admits that calling it a "planet" is a stretch; more likely, it's a "failed" binary star with a seriously stunted secondary. However, he notes that a massive planet might conceivably have formed closer in and then been tossed outward by a chance encounter with another large planet soon after the young star formed.

The true nature of 1RXS J160929.1-210524's companion probably won't become clear anytime soon. Its orbital period is likely thousands of years. At best, the team hopes to confirm that the star and its companion are moving together in space. "If we confirm that this object is indeed gravitationally tied to the star, it will be a major step forward," says Lafrenière. Those observations will have to wait until next spring, when the pair emerges from behind the Sun.

The observers have submitted their findings to Astrophysical Journal Letters for publication, but you can get a sneak peak in this online posting.

Oh, how I wish the Hubble Space Telescope had been around in the 1840s. That's when a star in the southern constellation of Carina brightened dramatically and for a time became the second-brightest star in the nighttime sky.

In the decades afterward, astronomers noticed an expanding shell of matter surrounding the perplexing star. The double-lobed glow, now known as the Homunculus Nebula, wasn't growing fast enough to be debris from a supernova blast. And the star itself, Eta Carinae, survived. It slowly faded to 8th magnitude, only to flare again in the late 1990s.

Astronomers have long regarded Eta Carinae as a supernova impostor, believing that in 1843 this stellar behemoth somehow burped a dozen Suns' worth of gas and dust into space and then settled down. Outweighing our Sun by 90 to 100 times, it probably had half again that mass when it formed a few million years ago.

Until now, the most common explanation has been that the star's intense radiation blew matter off its surface at prodigious rates. Such an effusive solar wind wouldn't be extremely fast, not even close to the velocity of a supernova's blast, which seemed to match the expansion rate of the nebula nicely.

But new research suggests that this megastar might have had more going on. In September 11th's Nature, Nathan Smith (University of California, Berkeley) reports finding faint filaments near the star racing outward at a few thousand miles (3,500 to 6,000 km) per second — much faster than anything observed in the Humunculus Nebula to date.

He tracked the nebula's outflow two ways. A spectrometer attached to the Gemini South 8-meter telescope high in the Chilean Andes recorded the movement of helium atoms, which have a strong infrared emission at 1.08 microns. Then, hopping over to the Blanco 4-meter telescope at nearby Cerro Tololo, he clocked velocities using Doppler shifts at deep-red wavelengths emitted by nitrogen-rich gas.

To Smith, the evidence suggests that Eta Carinae's 1843 eruption resulted from a violent disturbance within the star. "Rather than a steady wind blowing off the outer layers," Smith comments in a press release, "it seems to have been an explosion that started deep inside the star and blasted off its outer layers."

Smith believes a new kind of disruption must be involved that causes the innards of such massive stars to become highly unstable without blowing themselves to smithereens.

However, not everyone thinks Eta Carinae is the source of the observed outburst. This star has a smaller, hotter companion in a looping orbit that periodically brings the two within 1 or 2 astronomical units of one another, and some astronomers think it could be stirring up trouble instead.

"There is strong disagreement about the nature of Eta Carinae," comments Theodore Gull (NASA/Goddard Space Flight Center). "There is no reason that the secondary could not have thrown out that much material and more."

Smith doesn't find that plausible. "The companion star has a very close passage every 5½ years, but Eta Carinae doesn't have a huge eruption every 5½ years," he counters. "Instead, something wild happened to the primary star in 1843."

Don't get the idea that we've found every kind of astronomical object there is in the universe. In a paper to appear in the Astrophysical Journal, astronomers working on the Supernova Cosmology Project report finding a new kind of something that they cannot make any sense of.

The project used the Hubble Space Telescope to monitor very distant galaxy clusters for supernovae. On February 21, 2006, in the direction of a far-away cluster in Bootes named CL 1432.5+3332.8 (redshift 1.112, light travel time 8.2 billion years), Hubble began seeing something brighten. It continued brightening for about 100 days and peaked at 21st magnitude in two near-infrared colors. It then faded away over a similar timescale, until nothing was left in view down to 26th magnitude. The object brightened and faded by a factor of at least 120, maybe more.

The mystery object did not behave like any known kind of supernova. It is not even in any detectable galaxy. "The shape of the light curve is inconsistent with microlensing," say the researchers. They recorded three spectra of it — and its spectrum, they write, "in addition to being inconsistent with all known supernova types, is not matched to any spectrum in the Sloan Digital Sky Survey database" of vast numbers of objects. "We suggest that the transient may be one of a new class."

What's its distance? That would certainly be a first step to figuring it out, but only the broadest constraints can be put on its distance. Its lack of parallax motion means that it can't be closer than about 130 light-years, and a lack of cosmic hydrogen absorption in its spectrum means that it can't be farther than 11 billion light-years (when "distance" is defined by light travel time). That leaves a lot of leeway.

Here is the group's paper with all the details. The lead author is Kyle Barbary (University of California at Berkeley).

Any ideas? Put 'em in the comments below! (Please read the paper first, and post ideas that fit the observations.)

As if gamma-ray bursts weren't nasty enough, astronomers announced today that the brightest GRB ever seen shot a double-barrel blast toward Earth at near-light speed. One jet was incredibly narrow, and was nested inside a wider jet. It's like shooting a gun with a deadly laser beam embedded within a lethal spray of buckshot.

The evidence for this double-barrel blast comes from a gamma-ray burst detected by NASA's Swift satellite on March 19, 2008. GRBs are intense explosions that appear about once per day from random directions in space. Most GRBs occur when the core of a massive star collapses to form a black hole. Infalling stellar gas forms a disk around the black hole, and some of that material is shot away from the black hole in two jets traveling in opposite directions at near the speed of light. These jets can be likened to cosmic blowtorches whose energy boggles the imagination. For several seconds to several minutes, the gamma rays from these jets can greatly outshine an entire galaxy's worth of stars.

Normally, GRBs are detected in gamma rays and X rays. Eventually, the jets slam into surrounding gas clouds and dissipate their energy, generating an afterglow that astronomers can detect in visible light or in X rays. This optical emission is extremely faint and comes many minutes or hours after the burst itself. But in this March 19th burst, optical telescopes recorded a flaring source that peaked at about magnitude 5.3, visible to the naked eye from a dark site. If this doesn't sound particularly bright, then consider the distance — the GRB took place 7.5 billion years ago, effectively halfway across the visible universe. In other words, we are looking so far back in space and time that the star exploded several billion years before the solar system had even formed! For about 40 seconds, the GRB's optical flash was by far and away the most distant object that could be seen with the naked eye.

The immediate and obvious question was, "Why was this burst so bright?" In a paper published in the September 11th issue of Nature, Judith Racusin (Penn State University) and 92 coauthors provide an answer. The Swift satellite usually detects evidence of one jet slamming into nearby gas clouds and breaking up. But in this case, Swift found two "jet breaks," one from a very narrow jet and one from a much wider jet. The narrow jet has an opening angle of just 0.4 degrees, whereas the the wider jet had an angle of about 8 degrees. The GRB was so bright because the narrow jet was aimed exactly toward Earth. Swift's observations indicate that the particles in the narrow jet traveled at an astounding 99.99995% the speed of light.

As Racusin explains, "If the narrow jet was not pointed at us, we would not have seen its signature." A jet this narrow is so pencil thin that a satellite like Swift might see just one per decade. Since very few GRBs would be so perfectly aligned to aim their narrow jets toward Earth, this implies that most or all GRBs produce a narrow jet within a wider jet. (And since GRBs probably produce jets that shoot away in opposite directions, they are actually producing two narrow jets inside wider jets.)

GRBs were already known to contain staggering amounts of energy. But Racusin adds, "If all GRBs do have these narrow jets, it could potentially double (or more) the amount of energy that would be emitted by these explosions." Such a jet aimed at Earth from a collapsing star in our Milky Way Galaxy would seriously damage our atmosphere, perhaps triggering a mass extinction. Fortunately, only a tiny percentage of stars generate GRBs, and it's extraordinarily unlikely that one would occur in our galaxy with the perfect geometry to aim the barrel of the gun directly at Earth. GRBs are indeed nasty critters, but despite what you might have seen in sensationalist TV shows, they pose such a negligible threat to humanity that you should not lose any sleep over them. Still, we can marvel at Mother Nature's creativity and fury.

Courtesy calls to asteroids are relatively routine for NASA's interplanetary spacecraft — they've logged seven so far, dating back to 1991.

But for the European Space Agency, flying past one of these rocky bodies is wholly new territory. So you can understand why European planetary scientists are thrilled with their Rosetta spacecraft, which yesterday zipped past minor planet 2867 Steins at 18:58 Universal Time (2:58 p.m. EDT). All told, 15 different experiments gathered measurements during a brief encounter 224 million miles (2.41 astronomical units) from Earth.

The meeting wasn't particularly fast as flybys go, under 5½ miles per second, but Rosetta's ability to follow a rapidly moving target limited the closest approach to 500 miles (800 km). Even from this distance, the main camera should have recorded surface details only 100 feet (30 m) across during a "movie mode" that snaps images every 2 seconds.

However, an as-yet unidentified software parameter caused the craft's highest-resolution camera to shut itself down unexpectedly 9 minutes before the flyby. The instrument returned to normal operation a few hours later, but the best shots were irretrievably lost.

Fortunately, a wide-field camera continued clicking away — showing an angular, heavily cratered body that, from one angle, looked a bit like a classic, brilliant-cut diamond suspended in space. See ESA's movie of the flyby. "We've observed a new jewel in the solar system," commented H. Uwe Keller, principal investigator for the OSIRIS camera. Steins turns out to be a bit bigger than expected, measuring 3.7 by 2.5 miles (5.9 by 4.0 km) and a bit darker too (35% reflective).

Like most of the other asteroids seen at close range, Steins is one beat-up piece of interplanetary real estate. The images show a pair of craters more than 1 mile across, along with a curious seven-crater chain. Most likely, Keller says, this body is shattered throughout its interior.

To the eye, Steins looks bright gray. Based on spectra gathered prior to the flyby, astronomers had classed it as an E-type asteroid, with a surface dominated by the silicate mineral enstatite. Steins is the first E asteroid to be seen up close. Most likely it's a fragment from the crust of a much larger body that melted throughout eons ago before being shattered to smithereens.

Since Rosetta also targeted Steins with its mapping spectrometer, mission scientists should be able to discern whether the asteroid is a close spectral match to distinctive, enstatite-rich meteorites called aubrites.

Launched in 2004, Rosetta wasn't designed to be an asteroid chaser — it's en route to an extended rendezvous with (and a landing on!) Comet 67P/Churyumov-Gerasimenko in May 2014.

The spacecraft's circuitous trajectory, involving three flybys of Earth and one of Mars, also includes two asteroid flybys to give scientists and their instruments some target practice. The second of these, with much larger 21 Lutetia, is still two years away.

News has been sparse in recent weeks about Phoenix, NASA's newest Martian lander, and that probably suits the craft's handlers just fine. They've been working steadily but carefully to squeeze the most science of out a mission that will likely end once winter sets in a few months from now — and the clock is ticking.

Back on August 29th, Phoenix surpassed the 90-day milestone of its primary mission. I hesitate to say "completed" because, for all this lander has accomplished so far, a major objective still needs to be checked off the "to do" list: analyzing the water ice that lies abundantly beneath its footpads.

The ice has tantalized scientists since the first days after landing, when it became clear that plenty of the white stuff was within reach of Phoenix's 7.7-foot-long robotic arm. But getting scoopfuls of it (from a trench dubbed "Snow White") into the experiment hoppers hasn't been easy. The mix of icy shavings and soil particles clings tenaciously to the inner surfaces of the arm's scoop, and the Phoenix team is still working on a better delivery technique. Rumor has it they'll try again next week.

But other aspects of the mission are going well. Ice-free dirt samples have made into the tiny ovens of the Thermal and Evolved Gas Analyzer (TEGA) and another three samples to the lander's miniaturized wet-chemistry laboratory (WCL). Daily weather measurements are piling up — those should start getting really interesting now that northern summer is over and the Sun has started dipping below the horizon each night.

The science team has gotten a green light from NASA managers to keep digging, sniffing, and tasting through the end of September, but how much longer Phoenix might last after that is anyone's guess. I'm sure plenty of bets are on the line at the science operations center in Tucson, Arizona, and the Jet Propulsion Laboratory in Pasadena, California.

Phoenix sits amid polar terrain with a subtle polygon-shaped texturing that betrays how the ice is distributed just below the surface. Think of a sheet of bubble wrap (the kind used for shipping packages), and you'll get the idea. In some spots mounds of ice about a yard across lie barely covered with ruddy dirt, whereas the dirt layer extends deeper in the shallow troughs between them.

Recently Phoenix's excavations have shifted to a trough that's within arm's reach, and last weekend the robotic arm gathered up a sample dug from a trench (nicknamed "Stone Soup") about 7 inches (18 cm) deep.

One puzzling result followed a test of the soil's water content using a fork-like probe on the end of its sampling arm, which passes electrical current through the surface layer. It seems the topmost dirt is dry as, um, dust — even though there's water vapor in the air above it. "The relative humidity transitions from near zero to near 100% with every day-night cycle," notes JPL investigator Aaron Zent in a September 4th press release, "which suggests there's a lot of moisture moving in and out of the soil."

Puzzled or not, Phoenix's scientists seem to be having fun — at least as evidenced by the whimsical names they assigned to landmarks in the lander's trenching area. A few others, besides Snow White and Stone Soup, are a sample called Baby Bear (dug from Dodo-Goldilocks), the Upper and Lower Cupboards, Wicked Witch, and Ichabod.

All these giddy names make me wonder just how much sleep the science team got back in May and June, when they reset their body clocks to coincide with the Martian day (24.6 hours long). Now they're back on a more restful 9-to-5 schedule, but the name game hasn't stopped. The last sample, delivered to a WCL cell just a couple of days ago, was dubbed Golden Goose 2.

"There's more than one way to watch a meteor shower," begins a new Science at NASA story. "One, the old-fashioned way: Find a dark place with starry skies and count the meteors streaking overhead. Two, the new way: Find a dark place with starry skies and then completely ignore the meteors. Instead, watch the Moon. That's where the explosions are."

For centuries, astronomers tried and failed to get solid evidence of the little flare of light that ought to result from a meteoroid hitting the Moon's night side. But that was before modern low-light imaging. About 115 of these events have now been recorded on video, simultaneously from different locations to ensure that they are not point meteors in Earth's atmosphere or glitches in the video chips.

Lunar-meteor watching has become its own little subsection of amateur astronomy. Observers added several more of these events to the archive during the Perseid meteor shower three weeks ago.

I find this too cool for words. A meteoroid just a few inches across will hit with the energy of roughly a hundred pounds of TNT, creating a flash in the lunar vacuum clearly visible to a videocamera on an amateur telescope in a backyard a quarter million miles away. The flashes fade out in less than a second, but they often last for enough video frames to provide good confirmation.

Read more at the NASA story by Tony Philips, which has further links. NASA also has prepared a FAQ and telescope tips for would-be lunar meteor hunters who'd like to get started.

NOTE: If you don't see any pictures in this article, try clicking here.

As a hard-core visual astronomer, I've been feeling starved for dark skies recently. From Boston, Massachusetts, I have to drive 4 hours to get to the "gray" zone — the second darkest — shown on the Light Pollution Atlas. And nowhere east of the Mississippi falls in the "black" zone. So I was thrilled when I was invited to speak at the Oregon Star Party.

This get-together for stargazers, astrophotographers, and equipment geeks is held annually at Indian Trail Springs in the Ochoco National Forest. Located some 150 miles east-southeast of Portland as the crow flies, this site is nearly ideal for astronomy. At an elevation of 5,000 feet, the air is thin enough to provide superb transparency yet thick enough to breath easily. Like all the land east of the Cascade and Sierra Nevada mountains, the countryside is fairly arid, with an excellent probability of clear skies during the summer. But it's high enough and far enough north to escape the searing heat and desperate dryness of the California deserts. Big stands of ponderosa pine, ideal for camping, alternate with open sagebrush flats that provide unbroken views of the sky.

There's a low glow along the western horizon from Prineville (7,500 people 40 miles distant) and Bend (80,000 people, 60 miles), but the only light in most of the sky comes from stars, airglow, and the zodiacal light. But I was reminded again that the phrase "dark sky" is really a misnomer. At any truly excellent observing site, the first thing you notice is how bright the sky is. The Milky Way is dazzling, casting enough light to walk around easily without a red flashlight. Even in my tent under the trees, I could see all my belongings by starlight alone.

I was there for three nights: Thursday through Saturday, and the conditions varied from very good to superb. Thursday, in particular, combined some of the best seeing and transparency that I've ever experienced. And as a bonus, the night was virtually windless, with low temperatures in the upper 40s (F).

I've attended many astronomy gatherings, but few as upbeat and well-organized as the OSP. The huge staff of volunteers anticipated all the problems and made everything run as smooth as clockwork. Several different observing lists were suggested for people who wanted specific goals to meet, with prizes awarded to people who finished all or most of the objects on the list. The most challenging list consisted of Markarian 205, a distant Seyfert galaxy or quasar, and seven dwarf galaxies from our Local Group, all very large and fantastically faint. I didn't finish the list because of the limitations of the 65-mm telescope that I had brought along, but I did get my first satisfactory sighting of IC 1613, an ultrafaint galaxy in Cetus.

Numerous talks and other activities were scheduled during daylight hours. Most popular was the raffle for door prizes — and no wonder! A huge list of donors supplied a vast array of goodies. Most glamorous by far was a 60-mm Takahashi APO donated jointly by Anacortes, Texas Nautical, and Takahashi. I figure that the value of the prizes, pro-rated by the probability of drawing one, must surely be greater than the very modest fee for attending the party. The swap table also attracted a huge throng, and all the talks were very well attended.

Many of the attendees and most of the organizers came from Portland's Rose City Astronomers club, a hotbed of amateur telescope making. I would guess that about two-thirds of the scopes on the field were commercial and one third homemade. String Dobs, modified truss-tube Dobs that usually contain three struts under compression braced by six cables under tension, are the most popular design, particularly in larger apertures. The Telescope Walkabout was fascinating, featuring detailed explanations of a half-dozen innovative designs.

My special thanks go to Chuck Dethloff, both for conceiving the Oregon Star Party in the first place and for letting me spend a couple of hours viewing showpiece objects through his 24-inch Dob.

So why not check out our list of annual events and find out what star parties will be held soon in your area? Try going to one — I bet you'll love it! And if you have any specially wonderful (or terrible) star-party stories that you'd like to tell, describe them as comments to this blog entry.

The past decade has seen so many incredible advances in astronomy that it would be hard to single out one as standing above the others. But near the top of my list is the work by Andrea Ghez (UCLA) and her colleagues to measure the mass of the Milky Way’s central black hole. In a paper posted on the Web last week, they derive a new and improved mass for our galaxy's monster in the middle.

The team’s pure measurement yields a mass of 4.1 million Suns with an uncertainty of only 0.6 million Suns. But if the black hole is assumed to be stationary with respect to the rest of the galaxy (and there's no evidence otherwise), its mass rises a bit to 4.5 million Suns with an uncertainty of only 0.4 million. This latter result is significantly higher than previous measurements made by Ghez’s team and by a European group led by Reinhard Genzel (Max Planck Institute for Extraterrestrial Physics, Germany).

A black hole of that mass has a diameter of 0.1 astronomical unit (about 9 million miles).

Why is this measurement so amazing? The center of the Milky Way is 27,000 light-years away, and it's hidden behind thick clouds of gas and dust along our line of sight. How do you measure the mass of an invisible object tens of thousands of light-years from Earth when even its surroundings are obscured from view?

Ghez and her team had to employ all the resources of modern astronomy: a really big telescope, detectors that operate in the infrared, and the relatively recent technology of adaptive optics (AO for short). Oh yeah, they also needed a lot of patience.

For the past decade, they have been observing the galactic center with the 10-meter Keck I and II telescopes in Hawaii. Keck gives them the brute-force light-gathering power to see stars in the galactic center. They observe at infrared wavelengths, which can penetrate the thick clouds of gas and dust. And most of all, they use AO, which involves a laser-generated artificial guide star and flexible, deformable mirrors to compensate for the rapid-fire blurring effects of Earth’s atmosphere.

The combination of these techniques allowed the group to resolve dozens of individual stars near the galactic center. Incredibly, the team could trace the curving orbital motions of several of these stars over more than a decade, and actually create a movie of these motions. Astronomers of just 25 years ago would have considered this magic.

The high mass of the Milky Way’s black hole, known as Sagittarius A* (pronounced "A-star"), made this possible. Anything orbiting near such a massive object is going to move really, really fast. These stars are whirling around the black hole at speeds exceeding 4,500 km per second (10 million miles per hour). One star in particular, dubbed S0-2, has been clocked at nearly 8,000 km/sec. By using simple orbital laws dating back to Isaac Newton in the 1600s, Ghez could use these stellar velocities to derive the mass of the central gravitating object.

In their new paper (accepted for publication in the Astrophysical Journal), Ghez and her team took into account various effects, such as uncertainties in star positions, ignored by in previous studies. “It’s been a bit like teenagers making emphatic but uninformed statements,” explains Ghez. “In our new paper, we try to take an honest look at where the problems are. We’ve learned that things are more complicated. We’re growing out of our teenage years!”

Besides coming up with a more precise mass measurement, the latest observations refine the distance to the Milky Way’s center: 27,400 light-years, with an uncertainty of 1,300 light-years.

In addition, the group finds no evidence that the central black hole is being gravitationally yanked around by the mass of another. This argues in favor of the team’s higher mass measurement. This new, higher mass value is also more consistent with predictions based on the famous relationship between black-hole mass and the total mass in the spherical component of large galaxies.

Here's the group's paper, their website, and
more imagery.