What do Joe DiMaggio, Elvis Presley, and Lucille Ball have in common? They've all been featured on U.S. postage stamps. And what do Apollo 11, the Viking landers, Skylab, and Mariner 10 have that the Pluto-bound New Horizons spacecraft doesn't? You guessed it: each has a stamp to call its own.

But things might change if the mission's scientists have their way. Led by principal investigator Alan Stern and colleague Dan Durda (Southwest Research Institute), they're rounding up support for a stamp that shows New Horizons zipping past Pluto. The online petition they've started urges the Citizen Stamp Advisory Committee to recommend just such a stamp to the Postmaster General.

A talented space artist, Durda has even produced convincing "concept art" for the proposed postage, though the U.S. Postal Service will commission its own artwork if the stamp is approved

"The nation has an opportunity to honor a truly exemplary accomplishment of humankind in general, and the U.S. space program in particular," note the petitioners. Pluto has made it onto a U.S. stamp before, back when it enjoyed full planetary status, but that was way back in 1991 — and the tag line reads "Not Yet Explored".

It's not like Pluto was intentionally being ignored, but getting a spacecraft there hasn't been easy — technically or politically. Back in the 1990s a Jet Propulsion Laboratory team led by Robert Staehle tried to make it happen, but NASA managers canceled the effort in 2000 before construction could begin.

After many machinations, the New Horizons effort was approved in November 2001. "Ten years ago," Stern says, "I promised Rob Staehle that after launch we'd apply for a stamp," and now he's made good on that promise.

New Horizons will sweep past Pluto and through its four-moon family on July 14, 2015 — the 50th anniversary of Mariner 4's historic first flyby of Mars. It's hard to believe that New Horizons has already covered more than 3 billion miles since departing Earth in 2006, and that its rendezvous with Pluto is just 3½ years away.

That's why the petition needs to be submitted soon, because the glacial process of getting this stamp approved and issued might take three years, by which time the spacecraft will be closing in on its objective.

The petition has just gotten under way, and so far it's only garnered 2,500 signatories. But Stern expects to reach his 100,000-name goal. Between now and March 12th, when the drive ends, Stern wants readers of S&T.com to do three things: "Sign the petition, tell your friends to sign, and have your friends tell their friends to sign."

For the past three months, my biggest job at Sky & Telescope has been writing the scripts for our SkyWeek television program. It's been the most fun I've had since the late lamented Night Sky magazine ceased publication.

I've always loved writing for a general audience that knows little or nothing about astronomy, and you can't get a lot more general than the audience reached by television. And as with the Constellation Close-up department that I wrote for Night Sky, it gives me infinite opportunities to explore all the areas of human endeavor that astronomy touches on -- which is to say almost everything. Science, history, archaeology, folklore, art . . . you name it.

This is also the most challenging job I've done for S&T. It's tough to wrap your mind around an entirely new medium; I would never have been able to do it without the advice and assistance of the brilliant people at Powderhouse Productions.

Above all, I owe a huge debt of gratitude to the amazing multitalented Shweta Krishnan — scientist, writer, artist, and videographer. Shweta used to be an intern at Sky & Telescope, and now works for Powderhouse. She's the one who conceptualizes what the whole thing will look like, finds illustrations and animations to match the text, and creates them when none is available. And she's the one who criticizes my scripts, decides when they're unillustratable, incomprehensible, or simply boring and tells me — in no uncertain terms — how to fix them.

SkyWeek currently airs in the cracks between programs on a few public television stations; we expect to expand our audience dramatically in the next few months. It's also available on our website at skyweek.com, and on YouTube.

I'm curious what people think about it. In some ways it seems like a piece of fluff — but I hope that it's a fun and occasionally enlightening piece of fluff.

A new study published in the Jan. 26 issue of Nature highlights a rising theme in the symphony of astrophysics research: When you can’t go to the stars, bring the stars to you.

In this case, an international team of researchers studied where galaxies get their magnetic fields by zapping a minuscule rod with lasers to make a proxy of the environment in a forming galaxy. Their result — the creation of tiny “seed” fields by a well-known theoretical effect — supports current ideas of how large-scale galactic fields could arise and adds to previous arguments against more peculiar explanations.

Vast magnetic fields exist in all galaxy types and even on cluster and supercluster scales. It’s thought that turbulence and rotation in forming galaxies may amplify already-present weak fields, creating large-scale ones, explains Lawrence Widrow (Queen’s University, Ontario), who was not involved with the new study. Where these seed fields come from remains an open question. They could be primordial, arising from fancy physics cartwheels in the early universe. But such fields are “fairly exotic,” Widrow says, and require a lot of assumptions about conditions at the cosmic dawn. A better option would be astrophysical causes — fields expelled by the first stars when they died explosively, or by madly gobbling black holes in galactic cores. Or, created by the Biermann battery process.

In a nutshell, a Biermann battery is the spontaneous creation of a magnetic field when a curved shock wave goes through hot, ionized gas. It’s a well-known theoretical effect, and astronomers have suggested it before as a solution to the cosmic magnetic field question. To test the idea, researchers set up a 500-micrometer-wide carbon rod in a chamber of helium gas and vaporized the rod with laser beams. The supersonic expansion of the vaporized carbon drove a shock in the gas, which, because the shock wasn’t perfectly spherical, created a magnetic field, explains coauthor Francesco Miniati (ETH Zurich, Switzerland). Such fields could easily arise in the collapsing gas that forms galaxies, where over several hundred million years gas dynamics would augment the fields enough to affect the galaxy’s evolution, Miniati and his colleagues conclude. How exactly those effects would manifest is still mysterious, he says. But because magnetic fields affect the motion of interstellar gas, they may regulate star formation in molecular clouds and confine superspeedy particles called cosmic rays.

The result matches what’s expected theoretically from shocks during the collapse of matter into protostars and galaxies, but it’s the first experiment to unequivocally produce the effect in a lab, says Dongsu Ryu (Chungnam National University, South Korea), who has written several review papers with Widrow on the origin of the universe’s magnetic fields.

Miniati acknowledges that “it is a bold extrapolation” to draw conclusions from an experiment roughly a trillionth of a trillionth the size involved in intergalactic fields. But due to the physics involved in this particular case he’s confident that such scaling is possible.

The Biermann battery could work in any collapsing or accreting material, meaning it could provide the seed for stars’ fields, too. Where it — and the other theories — can’t reach is into gigantic cosmic voids, where astronomers have also found hints of weak magnetic fields. But a 2010 paper by Miniati and Tony Bell (Oxford University) suggested that a charge imbalance caused by cosmic rays could explain those fields, providing another astrophysical explanation that removes the need for exotic primordial fields.

The International Telecommunication Union, an arm of the United Nations, recently announced with great fanfare that it intended to settle the "problem" of leap seconds once and for all. At their meeting on January 19th, the committee decided to kick the decision down the road for another three years. Procrastination — what could be more appropriate for an official international committee on time?

Truth be told, this choice was as good as any other. Leap seconds have been added periodically to keep the official time in sync with Earth's uneven, unpredictable rotation, most recently at the beginning of 2009.

These leap seconds upset techies, because they mean that the internal clocks inside devices can't run autonomously. Instead, somebody has to go in there every few years and set the clock back a second. So people who run computer networks would be much happier if leap seconds were abolished.

However, abolishing leap seconds would just kick the problem down the road for a millennium or two, by which time local noon (the Sun being at its highest) would occur several hours late. People seem (strangely enough) to be willing to put up with daylight saving time, but I doubt anybody would be happy having the Sun highest at 11 p.m.!

What's my opinion? It's a thorny problem without any good long-term solution. But I object on principle to bending people's behavior to suit the convenience of computer techies. Machines were meant to serve us, not the other way around!

For more information, see our online article on time.

It's now Day 2,923 of Opportunity's 90-day-long mission to explore the Martian surface.

Eight years ago today, this golf-cart-size vehicle thumped onto Meridiani Planum just three weeks after the arrival of its twin, Spirit. Assembled and launched on a tight schedule in response to the loss of NASA's two previous Mars missions, the rovers were equipped with cameras and spectrometers to help geologists learn whether and where water had coursed over the ruddy surface. The baseline mission for each was just 90 sols (Martian days) long.

Not even the most optimistic proponent could have foreseen that Opportunity would still be working — and fully functional — after all this time. Yet, in a way, this half of the mission was lucky from the start: it plopped right into a small crater full of easily accessed outcrops and scads of little round "blueberries" (hematite nodules) created in a watery environment long ago.

Today "Oppy" is perched on a rocky outcrop called Greeley Haven, a destination on the rim of Endeavour crater that the rover reached last August. To get there, it traversed 13 miles (22 km) over three years.

Now Martian winter is coming and, with it, diminished sunlight for the dust-covered "wings" that provide the craft with electricity. As a precaution, ground controllers have placed Opportunity on a sunny slope and tilted it for better solar exposure. It will remain there for several months until the Sun's rays start to strengthen in spring. (Spirit, located closer to the polar region, didn't survive the previous winter and has been silent since March 2010.)

Even while motionless, Opportunity will be pushing the boundaries of Martian science. "The top priority at Greeley Haven is a radio-science campaign to provide information about Mars's interior," says Diana Blaney, deputy project scientist, in a Jet Propulsion Laboratory press release. Doppler shifts in the rover's radio beacon provide a sensitive way to measure the wobble in the planet's rotation and, from that, an indication of whether the Martian core is molten.

With a diameter of 14 miles (22 km), Endeavour is big and rich with geologic promise. Orbital scans suggest that it's an ancient feature with clays and other water-influenced compounds in its rim and basalt-rich deposits on its floor. The project team is eager to start exploring these with their seemingly indestructible rover.

In a sense, Opportunity has just begun a brand new mission — and I wouldn't be surprised if we'll be celebrating a new wave of discoveries — and the ninth anniversary of its landing — a year from now. By then it'll have some company: Curiosity, NASA's Mars Science Laboratory is now en route and should descend into Gale crater on August 6th.

There’s no doubt ancient astronomers were clever folk. Realizing Earth was round, estimating the Sun’s distance, discovering heliocentricity — it’s quite a list. But Brad Schaefer (Louisiana State University) suggested at the recent American Astronomical Society meeting in Austin that we should add another light bulb to the glow shining from history: ancient astronomers may have corrected for dimming caused by the atmosphere, centuries before anyone came up with a physical model for it.

This dimming is called atmospheric extinction. Extinction happens because starlight has to pass through Earth’s atmosphere in order to reach us. But the effect isn’t uniform: if you spend time stargazing you’ve probably noticed that a star high up in the sky’s dome looks brighter than it does as it slides toward the horizon. That’s because light coming to us from near the horizon passes through more atmosphere than if it shines straight down from overhead. (The Sun looks redder at sunset and sunrise for the same reason.)

Astronomers have catalogued stars’ magnitudes for at least two millennia, all the way back to an ancient document called the Almagest. It was the Almagest that Schaefer began with — but his goal wasn’t to determine if astronomers in olden days accounted for extinction. He wanted to use the brightnesses reported in it to decide a long-standing debate over who wrote the catalog in the first place, Hipparchus of Rhodes (circa 150 BC) or Ptolemy of Alexandria (circa AD 150).

Some researchers have looked at the positions reported for the Almagest’s 1,000-plus stars to try to distinguish between the theories, but the differences aren’t conclusive. So Schaefer decided to try using atmospheric extinction to crack the case. Rhodes is at 36° north latitude and Alexandria at 31.2° N, which means the same stars will appear lower in the sky (and therefore dimmer) in Rhodes than they will in Alexandria. The star Canopus, for instance, is by modern calculations the second brightest star in the sky, after Sirius. Canopus should have looked 4th or 5th magnitude to Hipparchus but 2nd magnitude to Ptolemy, Schaefer says. (Astronomers’ magnitude system is also ancient, based on Hipparchus’s work: a magnitude 1 star is 2.5 times brighter than a star of magnitude 2.) By comparing the Almagest brightnesses against modern magnitudes — which are extrapolated to how they would appear outside the atmosphere — Schaefer should have been able to tell by the growing difference between the two values where the observer was. But he soon discovered a problem.

“You would expect that as you look further south the Almagest magnitudes would start … going up and up and up,” he says. “But when you look and see the real data, you see that they are not going up and up and up.” No matter how near the horizon you look, the error in the stars’ magnitudes compared to today’s values averages out to about zero. “Somehow somebody corrected the Almagest magnitudes for extinction. It’s the only way.”

When Schaefer looked at catalogs from two other renowned astronomers, al-Sufi (10th century) and Tycho Brahe (16th century), he also found extinction corrections.

The result has surprised many astronomers because there are no historical records mentioning extinction. The first physical explanation for extinction came in the 1700s from the French scientist Pierre Bouguer, and while extinction is obvious to an experienced observer, “it’s rather surprising that [the ancients] did a sophisticated and pretty accurate correction for something they don’t talk about and no one ever knew they knew about,” Schaefer says.

Several astronomers do remain skeptical and argue that scatter in the data may undermine Schaefer’s result. There's also the issue that no one knows how the ancient magnitudes were calculated, and other researchers have analyzed the Almagest brightnesses and not found extinction corrections. More than one astronomer said they want to see a detailed paper before deciding if Schaefer is right or wrong. Still, the overall consensus seems to be that “he’s onto something.”

How did the ancients do it? Not clear. Probably they watched stars that traversed large parts of the sky and determined how bright those stars appeared at different heights above the horizon. With those estimates in hand, they could eyeball stars that never rose very high and figure out how bright the stars really were based on their apparent magnitude and how far they were above the horizon. Schaefer says he did rough extinction calculations by eye while vacationing in the American Southwest that were pretty good. “It’s naked-eye backyard astronomy to the rescue of historical astronomy,” he laughs. Our readers are invited to try calculating for themselves.

Norman W. Edmund, legendary founder of a company offering a profusion of optics to the public for 70 years (and counting), died January 16th in Fort Lauderdale, Florida. He was 95.

Sidelined from serving in World War II by an early bout with tuberculosis, Norman Edmund got the idea to start selling optical parts that he acquired as war surplus. He formed the Edmund Salvage Co. and placed his first Sky & Telescope ad in the September 1945 issue. Taking up a full page, it began in bold type, "Unusual War Bargains in Lenses and Prisms." The listings included color filters, reticles, mirrors from tank periscopes, and a 1.8-inch f/11 achromatic objective for making your own small refractor.

That first ad also offered two sets of small surplus lenses and a 50-page booklet titled "Fun with Chipped Edge Lenses." Elsewhere in the same S&T issue, competitor Harry Ross proclaimed that his own products were "Not Salvage — Not Rejects — Not Junk!" Despite the dig, Edmund kept on selling the popular chipped-edge lenses (inexpensive seconds, aimed at experimenters) for decades to come.

Initially Edmund worked out of his home in Audubon, New Jersey. "I once heard that Norm kept his stock of lenses, etc., in boxes under his bed," recalls William E. Shawcross, former managing editor and later president of Sky Publishing Corp.


Then in 1948 Edmund opened a larger facility in nearby Barrington, New Jersey, and changed the name to Edmund Scientific Co. The firm soon attracted worldwide notice, and its product line grew to include a remarkable 3-inch f/10 Newtonian reflector for just $29.50. This scope came as kit and was "easily assembled; a nine-year-old can do it!" It had a cardboard tube, wooden legs, and interchangeable tripod heads for alt-azimuth or equatorial operation. (Full disclosure: This 3-inch was my first telescope. My brother and I pooled our allowances in 1956, and it opened the night sky to us.)

Longtime astronomy writer James Mullaney recalls, "I met Norman several times. The most memorable occasion was at a national convention of the Astronomical League in Haverford, Pennsylvania, I believe in the late 1950s. Buses took us to Barrington, and Norman was out behind the building grilling steaks for everyone with a chef's hat on!"

During the late 1950s and '60s the company expanded its line of traditional Newtonians, refractors, and mirror-grinding kits. When Norman Edmund's son, Robert, took the helm in the mid-1970s, the firm introduced the novel Astroscan, an all-red, low-power, 4-inch reflector for tabletop use.

Present-day Edmund Optics, where Robert continues as CEO, has a tribute to Norman on its website here.

On the afternoon of January 8th, a small group of journalists and scientists headed north from downtown Austin, the venue for 219th meeting of the American Astronomical Society, to the University of Texas campus. There we learned about HETDEX, the Hobby-Eberly Telescope Dark Energy Experiment, which David Lambert, the director of McDonald Observatory, introduced as the first major effort to "map the evolution of dark energy as a function of time."

The universe has been expanding since the Big Bang, but observations in the last couple of decades show that this expansion is accelerating, rather than slowing down. Dark energy was first postulated in 1992 as the hypothetical force that causes this stepped-up expansion. Calculations suggest that it constitutes about three-fourths of the energy in the universe — yet remains one of the least understood scientific phenomena.

Over three years, HETDEX will plot the three-dimensional positions of one million galaxies at different eras of the distant past, which astronomers will use to calculate how fast "normal" (baryonic) matter has been drifting apart since the Big Bang. In the process, the experiment will help generate what could be the grandest map of the universe yet.

"Humans have always been cartographers," says Gary Hill, the experiment's principle investigator. "This is the biggest map you're going to get."

HETDEX is not meant to answer all questions on the nature of dark energy, but it should eliminate a few theories and narrow the possibilities of what this phenomenon could be. Hill and his colleagues are looking for evidence of baryonic acoustic oscillations — "sound waves" that rippled through the hot plasma that pervaded space in the first 400,000 years after the Big Bang. Cosmologists think that when the universe began to cool, these perturbations left an impression, much like the crests and troughs created by a stone thrown into a pond, that the HETDEX team now hopes to chart spectroscopically. Dusting these ancient "fingerprints" should give the team an idea of how fast the early universe expanded, and the rate of its acceleration since.

Cultivating VIRUSes

The heart of this experiment is a new device called VIRUS, short for Visible Integral-Field Replicate Unit Spectrograph. Each VIRUS is made of 230 fiber-optic cables that feed light from a small part of the sky into a spectrograph. "It can be built on an assembly line," jokes Hill. "We are catching up with Henry Ford here."

HETDEX will eventually utilize 145 VIRUS assemblies to scan 400 square degrees of sky covering most of the Big Dipper — 2,000 times the area of the full Moon. While VIRUSes could work with any telescope in the world, the chosen scope for this experiment is the Hobby-Eberly Telescope at McDonald's Observatory.

The giant scope has an unorthodox design that is well-suited for spectroscopy. Its segmented primary mirror, measuring 36 by 32 feet (11 by 10 m), is technically the largest in the world. But only a portion of its light can be focused on the tracker that rides above it, giving the HET an effective aperture of 9.2 m that ranks fourth in size worldwide.

To map dark energy, the telescope is undergoing a makeover to deliver a wider field and to accommodate all those VIRUSes. The tracker now sits in a garage on the Austin campus, looking like a mere scaffold without the silver-coated relay mirrors that are now being polished at the University of Arizona in Tucson. The light from the primary, the team explains, will bounce off four other mirrors before it is fed to the VIRUSes. The base of the tracker is also being modified to support the weight of these four mirrors and 34,000 fiber-optic cables.

The entire unit will be dismantled and shipped to the McDonald Observatory sometime in June this year. Then the team will correct optical errors, and program the on 140 new-moon nights over a 3-year period. On days the HETDEX team is not tracking down evidence for dark energy, other research teams will be able to use the VIRUSes, which will become permanent additions.

Two data pipelines, quite aptly named Vaccine and Cure, will process the ginormous amount of data collected using these VIRUSes. They will look for the Lyman-alpha emission line of hydrogen, which will help them chart the position of a galaxy as a function of space and time. Lyman alpha has an ultraviolet wavelength of 121.5 nanometers, but the target galaxies are so far away that their emissions are redshifted to blue and green portions of the visible-light spectrum.

The team hopes to have its first results four years from now. Hill also hinted at a possible citizen-science project along the lines of Galaxy Zoo that might find a use for the data beyond HETDEX's goals.

Both HETDEX and its goals seem like wild science fiction, and at times our 1½-hour briefing felt more like a Steven Spielberg movie than astronomical research. But this unique undertaking in forensic astronomy is very real, and very promising. In four years dark energy may not be so dark after all.

We live in a golden age of automated sky surveys, and it's getting more golden all the time.

One way that sky surveys are changing astronomy is by producing gigantic numbers of high-quality light curves for new variable stars. Usually these are just byproducts of projects that were designed for other purposes. But if a sky survey can automatically measure the brightnesses of millions of stars over and over, why not save the data and mine it?

The largest such variable-star database yet has just been announced by the Catalina Sky Survey and the Catalina Real-time Transient Survey. Their job is looking for near-Earth asteroids and watching for transient events among the background stars and galaxies. But along the way they have collected 20 billion brightness measurements of 198 million stars and other objects. That's an average of 100 brightness measurements for each one. The objects range from magnitude 12.5 to 20 and span an area of just over half the celestial sphere.

The new light curves include more than 1,000 distant supernovae, some of unusual and novel varieties; about 3,000 other transient objects from flare stars and dwarf novae to erupting galactic nuclei; and tens of thousands of new variable stars of every other kind.

By comparison, the official General Catalog of Variable Stars, the bible of the field since ever, contains 43,675 named variables, and many of those have been poorly covered.

The Catalina light curves are uniform and consistent, with measurements typically accurate to 0.06 or 0.08 magnitude. "This set of objects is an order of magnitude larger than the largest previously available data sets of their kind," says Andrew Drake (Caltech), lead author of a poster paper presented at the American Astronomical Society meeting in Austin last week.

The project operates with an open-data philosophy. "We discover transient events and publish them electronically in real time, so that anyone can follow them and make additional discoveries," says Drake. In this way it's a precursor to the much bigger Large Synoptic Survey Telescope (LSST) project, which should begin watching the sky with a unique, wide-field 8.4-meter scope by the end of this decade. (The LSST's capabilities will be mind-boggling: it's designed to measure everything across half the celestial sphere to magnitude 24.5 in six colors an average of once every three or four days for at least 10 years.)

"We hope to set an example of how data-intensive science should be done in the 21st century," says George Djorgovski, principal investigator of Catalina's transient survey.

The observations so far come from the University of Arizona's 0.7-meter telescope on Mt. Bigelow in Arizona. They run from 2004 through 2011. The team says it soon plans to include data taken with a 1.5-meter telescope on Mt. Lemmon in Arizona and a 0.5-meter telescope in Siding Spring, Australia.

Such data riches do not render traditional variable star observing obsolete, Drake emphasizes. The Catalina survey can't measure stars brighter than 12th magnitude; they saturate the pixels. And it avoids the entire wide band of the Milky Way, because there the stars are so numerous that their images in the system often overlap.

And, says Drake, "There is still significant important work to be done by observers carrying out detailed observations of small numbers of objects. For example, the Catalina Surveys rely on such followups to tell us what interesting objects are doing on short timescales."

More information.

There’s something strange obscuring the light from a cool, low-mass star observed by NASA’s Kepler mission. Every 15.685 Earth days, KIC 12557548’s light dims for about 1.5 hours. The dips in starlight aren’t always the same — some events block more light than others — so the occultations don’t look like the regular blip caused by a planet passing in front of the star. After considering various options, an international team of astronomers reported recently that the signal might be from debris thrown off by a small rocky planet as it disintegrates under the star’s glare.

Astronomers found what looks like an evaporating gas giant in 2003, but if real KIC 12557548’s world would be the first solid exoplanet seen dematerializing.

So far there isn’t a lot of information to go on. The transits’ regularity argues against wildly off-kilter orbits, and observations seem to rule out anything larger than three Jupiter masses. The comet-like tail the researchers suggest as an explanation can’t be made of hydrogen, like the tail seen from the 2003 discovery HD 209458b, because the gas wouldn’t block enough light: particulates (like dust) are needed. The planet needs to be pretty small, too — the astronomers assume a little less than 2 times Mercury’s mass for their calculations — in order to not show up in the observed light dips. It also needs to be small enough that dust can overcome the body’s surface gravity and launch into space.

A super-Mercury like the one the astronomers propose would only survive about 200 million years before it vaporized. The authors note that “this is probably less than the age of the star, but not alarmingly so.” The “not alarmingly so” means that the timescales for the star’s age and for planet evaporation are about the same, which is good for the dissipating exoplanet hypothesis because it isn’t impossible for the planet to still be there. On the other hand, it’d be safer for the hypothesis if the disintegration time was significantly longer than the star's age.

Spectral observations may be able to determine if the planet and its tail are there and what the tail is made of. The astronomers put their bet on pyroxene, a silicate mineral found in Earth’s crust and mantle (and in meteorites) that should survive close proximity to KIC 12557548 long enough to block starlight before the grains vaporize.

Sky & Telescope's March 2012 issue is now available to digital subscribers. Some print subscribers have already received it, and it's officially on-sale at newsstands starting January 31st.

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The March issue features a special report on a long-standing stellar mystery in astronomy: the nature of the star Epsilon Aurigae. Epsilon Aur has befuddled observers since they first noticed variations in its brightness nearly 200 years ago. Every 27 years the star dims for at least 18 months — but there’s no companion star to be seen that could explain the dip by blocking the light in an eclipse. Now, an international campaign by amateur and professional astronomers may finally have built up enough evidence to clear up the enigma.

The solution? A thick, elongated disk surrounds a hidden hot, massive star, and as this disk passes in front of the bright, white-yellow star that we normally see, the light dims.

The details of this picture look pretty solid, and indeed when the issue went to press the staff here were pretty much convinced. But not everyone’s onboard yet. While at the American Astronomical Society meeting in Austin, I ran into Edward Guinan (Villanova University) and his student, Cole Johnston. They were presenting work done with an American, Czech, and Croatian team that suggests the primary star is roughly five times more massive than reported by Robert Stencel (University of Denver) and his collaborators in S&T. Stencel says he isn’t convinced by the other team’s high-mass results, and the debate continues. As Stencel puts it, “That’s what makes Epsilon Aurigae such fun — honest people can disagree!” You can listen to an interview with Stencel in our Beyond the Printed Page content.

Epsilon Aurigae isn’t the only mystery in the March issue. A strange glow from Venus’s nightside, called the ashen light, has puzzled astronomers even longer than Stencel's eclipsing binary. Thomas Dobbins explores what this light might be, admitting that he, too, once thought it was merely a trick of the eye until he saw it for himself.

Tracking down where the Sun might have shone its first light, spotting all five classical planets, and picking telescopes for peeking at the Sun — all these adventures and more can be had in the March issue. To find out more, read our online Table of Contents.

Here's an irony for you: This week, during a meeting of the American Astronomical Society, researchers described an intriguing black hole dubbed H1743-322 that burped up two massive blobs of superhot matter in 2009. Key to the finding were observations from NASA's Rossi X-ray Timing Explorer — which ground controllers had shut down for good just days before the meeting, on January 5th, after 16 years of operation.

As project scientist Tod Strohmayer explains in NASA's announcement, "The spacecraft and its instruments had been showing their age." Partly for this reason — but largely because the space agency had too little funding to operate all its spacecraft — NASA managers followed the recommendation of an external review panel and opted to terminate the mission's funding.

Launched in December 1995 as the X-ray Timing Explorer, the 1½-ton craft was renamed a few months later to honor Bruno Rossi (1905-93), a pioneer in the fledgling field of X-ray astronomy during the 1960s.

RXTE was one of those workhorse spacecraft that you rarely hear about. It was tasked with recording very short variations in the output of cosmic X-ray sources. RXTE's three instruments allowed high-energy specialists to monitor even relatively weak events that varied as rapidly as a few microseconds. The spacecraft kept an X-ray eye on large swaths of sky over a wide range of energies, from 2,000 to 250,000 electron volts (a typical dental X-ray is around 60,000 eV).

These capabilities might not sound very exciting — it's not the kind of mission for which NASA's public-relations team spends big bucks to create slick artist's concepts and dramatic videos. But they were crucial to understanding the detailed workings of white dwarfs, neutron stars, and black holes — and the spacecraft could be slewed quickly to observe an outburst as it happened.

The first big news coming from the RXTE mission came in 1997, when astronomers used RXTE's timings to show that the gravitational attraction of spinning black holes is strong enough to drag along the very fabric of space and time in its vicinity. This relativistic "frame dragging" had been predicted by Albert Einstein in 1918 but never before observed.

In the late 1990s, NASA scientist Chryssa Kouveliotou and others used RXTE to confirm the existence of magnetars, rapidly spinning neutron stars with magnetic fields more than 100 trillion times stronger that the Sun's. Those observations garnered Kouveliotou, along with Robert Duncan and Christopher Thompson, who predicted the existence of magnetars, the 2003 Bruno Rossi Prize for high-energy astronomy.

A frequent target for this timing machine was Eta Carinae, the southern sky's famously supermassive star that flared to prominence in the mid-1800s, getting so bright that it rivaled Sirius. RXTE observations offered the first hints that Eta Carinae might actually be two closely paired giant stars, suspicions that were confirmed a few years later by another space observatory, the Far-ultraviolet Spectroscpic Explorer.

In fact, RXTE observations have been used in more than 2,000 refereed articles over the years — not bad for a craft that cost only a few million dollars per year to operate. A fuller list of the mission's scientific highlights is here.

So now what? RXTE offered unique capabilities that aren't matched by other current spacecraft, such as NASA's Swift or Japan's Suzaku. One partial replacement will be India's Astrosat, to be launched later this year, which should provide limited monitoring of transient X-ray sources.

AUSTIN — Astronomers have announced the detection of a system of three candidate exoplanets, each with a radius smaller than Earth’s. The planetary system’s host star, dubbed KOI-961, is a dim red dwarf in the NASA Kepler mission’s field of view. The planets are among the smallest discovered around a Sun-like star and is the most compact system to date. They are “an incredible find,” says Sara Seager (MIT), who was not involved with the study.

The three bodies were found when they repeatedly crossed in front of KOI-961, creating minute dips in the star’s light. So far they’re still candidate planets because astronomers haven’t detected them using other means. The most common follow-up method measures wobbles in the star’s position along our line of sight caused by its planets as they orbit, from which researchers can calculate the planets’ masses. But KOI-961 has a visual magnitude of about 16, which is a couple of magnitudes too dim for precise wobble measurements using current instruments.

Still, the international team of astronomers was remarkably cautious in its analysis. The researchers spend most of their 13-page paper minutely considering the host star’s properties and various alternatives to the triple exoplanet result. And with such a high number of transit observations — several hundred crossings were observed for the innermost planet, says team member John Johnson (Caltech) — it’s highly unlikely the signals aren’t real.

The KOI-961 system came to the researchers’ attention through a lucky break, Johnson explains. One of Johnson’s collaborators is a British amateur astronomer named Kevin Apps, who in his spare time “devours” astronomy research papers and memorizes catalogs, which he can compare in his head. It was Apps who alerted Johnson’s team to the fact that KOI-961 had properties eerily similar to those of Barnard’s Star, one of the nearest and best-studied stars in the sky.

“It was as if it was the exact same star,” Johnson says. Using Barnard’s Star as a base, the astronomers determined KOI-961’s properties to high precision. From those estimates they found sizes for the three planets: 73, 78, and 57 percent of Earth’s average girth, from nearest to farthest from the star. The smallest, KOI-961.03, is about the same size as Mars. None resides in KOI-961’s habitable zone.

Without mass measurements the astronomers don’t know the planets’ densities, so they can’t say what they’re made of. But common sense dictates they’re probably rocky, Johnson says. Even if the planets were made completely of iron (which is improbable at best), they would still be less than two Earth masses.

The new exoplanets have raised hopes of detecting planets around more dwarf stars, allowing astronomers to better understand how many of these small stars have families of their own. “It’s kind of like cockroaches,” Johnson says. “If you see one…”

AUSTIN — Two bullets of high-energy material seen shooting into space in 2009 may help astronomers understand how black holes create the powerful jets sometimes observed streaming out from their poles. The observations, reported January 10th at the American Astronomical Society’s January meeting, will also appear in the Monthly Notices of the Royal Astronomical Society.

The astronomers combined radio maps from the Very Long Baseline Array with observations from the Rossi X-ray Timing Explorer, a NASA mission that shut down last week, to study an object known as H1743-322.

H1743-322 is thought to be a binary system, containing a small black hole and a regular star from which the black hole siphons material, creating an accretion disk around itself. First discovered in 1977, the system is about 28,000 light-years away (near our galaxy’s center) and appears to eat a big meal from this disk about every 8 months, says Gregory Sivakoff (University of Alberta), who presented his team’s results in a press conference at the AAS.

What’s curious about the dual black hole burp isn’t so much the jet bullets — though those are cool, too — but that their appearance seems to coincide with the disappearance of cyclic X-ray variations called quasi-periodic oscillations, or QPOs.



Astronomers don’t entirely agree on what causes QPOs. One leading theory is that a blob in the accretion disk produces the signal. As the blob spirals inward toward the black hole the frequency of the X-ray emission would naturally increase — an increase seen in the days leading up to H1743-322’s outburst in early June, even while its radio emissions stayed steady — because the blob is following an increasingly tight orbit. But shearing effects so near to the beast could stretch the blob out, adding complications that aren’t observed.

It’s possible that the QPOs instead arise from warping in the disk itself, caused as the spinning black hole drags spacetime around with it and affects emission seen from the orbiting material. A third idea is that the magnetic field in the accretion disk is to blame, explains Sera Markoff (University of Amsterdam), a theorist on the new paper. Magnetic fields are thought to pervade the disk and are intimately involved in jet launching. It could be that QPOs are actually related to structures in the magnetic field near the black hole, lit up by ionized, superhot gas, she says.

A lot is still unclear in this picture. “The disappearance of the QPOs and the launching of the transient jet is an important piece of evidence that ties together the accretion disk and the launching of jets,” Sivakoff said. “This is the first piece of the puzzle.”

Jets are something like a manifestation of magnetic fields, Markoff explains, since the hot, ionized gas is funneled out of the system along the magnetic field lines. Further study of H1743-322 and other sources should help astronomers understand how jets form, which has been a mystery for decades, she says.

Slightly distorted images of distant galaxies are giving astronomers a big-picture view of where the universe’s dark matter hangs out. The results, reported January 9th at the American Astronomical Society's winter meeting, represent the largest-scale survey yet of the unseen stuff that makes up more than 80% of cosmic matter.

Part of the team’s initial results are two-dimensional maps of the dark matter’s structure. The maps reveal clumpy filaments outlining gigantic empty spaces, closely — though not exactly — aligned with where visible galaxies cluster. The web looks much like detailed theoretical simulations produced a few years ago by the Millennium Simulation project at the Max Planck Institute for Astrophysics. But these maps are real.

“This is an amazing, amazing result,” says Jason Rhodes (JPL), who attended the team’s afternoon science session. The project — the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) — is not the deepest survey ever conducted, “but it’s still very impressive.”

CFHTLenS looked at more than 10 million galaxies in four patches of sky, covering a total of 155 square degrees — about the area covered by your outstretched palm, says team member Catherine Heymans (University of Edinburgh). The light from these galaxies doesn’t come to Earth in a straight line. Instead, the light is “weakly lensed,” distorted slightly as it passes matter lying between the galaxy and us.

The distortion happens because matter creates wells in the fabric of space-time, much like what happens when objects are set on a stretched rubber sheet. A marble rolling on that sheet won’t follow a straight line; instead, it’ll follow the rubber’s curvature. The same thing happens to photons coming to us from faraway places: matter along its path acts like a lens and bends the path from a straight line. Strong lenses create mysterious arcs of light, such as those seen several years ago by the Hubble Space Telescope’s Advanced Camera for Surveys. But the galaxies in this survey are lensed only about 1%, nowhere near enough to create such banana-shaped images.

“If you drew a circle and distorted it by one percent, you would not be able to see it by eye,” Rhodes says. Analyzing the observations was a technical feat, requiring the researchers to deal with sources of error that could introduce fuzziness greater than that tiny signal. Team member Thomas Erben (Bonn University) noted with a wry smile that they originally expected the analysis to be done in one year. It took four.

“This is 100 times larger than any previous deep survey,” Heymans says. While the web looks delicate, the structures it marks are humongous. The largest shot of the sky, that taken in winter, spans 1 billion light-years.

“If you focus on the highest mass places . . . those are really hosting giant monsters, clusters of galaxies,” says team member Ludovic Van Waerbeke (University of British Columbia), pointing out bright knots in one of the images. The mass of the largest clusters is on the order of 100 trillion times the mass of the Sun, he says. “Those are really, really, really big clusters.”

The results are still preliminary. The team hasn’t completed a three-dimensional map yet, nor are the astronomers sure the small discrepancy they currently see between where the galaxies are and where the dark matter lies will prove to be real as they continue their analysis. As of yet the project has found nothing that disagrees with modern cosmological theories, including Einstein’s theory of gravity.