An Eye on the Sky
Forty miles northwest of MIT in the woods of Westford, Massachusetts, a barely marked turn leads down a narrow dirt road to a small white building. It’s unremarkable from the outside, save for the two domes that rise, like squat silos, almost to the height of the surrounding oaks. Inside each dome is a telescope. When the Wallace Astrophysical Observatory’s mechanical roofs are peeled back on clear evenings, MIT astronomers practice the science of studying the night sky.
On a cold, dry night in early February, two such observers are hoping for good luck. It’s well past midnight and an icy 3 °F, and Wallace site manager Timothy Brothers and Stephanie Sallum ‘12 want to be the first astronomers to photograph Quaoar, a thousand-kilometer-wide object a billion kilometers past Pluto, as it passes in front of a star. Brothers and Sallum aren’t certain they will be able to spot Quaoar, which is named after a Native American creation god. According to MIT researchers’ calculations, it should occlude the star at 5:03 a.m. over the Atlantic Ocean. These two are betting that a telescope in eastern Massachusetts will be close enough to catch it.
The Wallace Observatory opened its doors 40 years ago this fall, and a look at its history—and through its logbook, which dates back to 1971—reveals how the science of observing has evolved with technology. In 1971 Wallace’s computer controls made it cutting-edge; today the observatory’s equipment is relatively modest compared with the enormous telescopes trained on the skies in more modern facilities. But MIT’s observatory has grown with the times, making strides in teaching and research. As it turns 40, Wallace appears poised to maintain a special place at MIT for far longer than its creators imagined.
Low haze, thick clouds throughout southern sky. I learned how to play solitaire. Amanda just woke up.
—Wallace logbook, July 16, 1989, 1:00 a.m.
The facility has the look of a perfect hideaway from which to observe planets and stars. The building’s compact single story houses a computer data room, a kitchenette, an abandoned darkroom, and a workshop for fixing telescopes. A sign on the door of a tiny room containing bunk beds reads: “QUIET PLEASE, ASTRONOMER SLEEPING.” Celestial objects don’t move according to human schedules; when there’s an important astronomical event to observe, its timing dictates work hours. “If an event is scheduled to happen at three or five in the morning, it might be better to get out here and have a few hours’ sleep beforehand,” explains Brothers.
At 2 a.m. on February 11, he and Sallum are awake, preparing for their Quaoar observation. They bring out snacks—cinnamon raisin bread and Nutella—and roll back the roof to test the cameras hooked up to their telescopes. Such cameras can snap thousands of images during a single night to track what is happening in the cosmos.
Brothers is perched in the dome that houses the facility’s 16-inch telescope—a cold silver instrument that dwarfs the observer. Up a spiral staircase from the main office and through a trap door sits the larger 24-inch telescope, used mainly for advanced research; it’s out of commission tonight for a control-system upgrade. The inch measurements refer to the diameter of each telescope’s main mirror. The bigger the mirror, the more light a telescope can collect, yielding a clearer picture of the sky.
Occultations, which occur when a celestial object like Quaoar passes in front of a bright star, are a frequent focus of Wallace researchers. (They also often look for exoplanets, or planets outside our solar system, as they transit stars.) “You can’t clearly image these objects from Earth—they’re too small and too far,” says Carlos Zuluaga, a research associate in the department of Earth, Atmospheric and Planetary Sciences (EAPS) who works closely with the Wallace Observatory. But by observing the way they block the star’s light, researchers can glean information about the objects, many of which are far-flung remnants from the solar system’s formation. Charting how long a passing object like Quaoar appears to snuff out a star can help scientists calculate the object’s size.
This method of observation is a powerful tool in astronomy, says Zuluaga: “We know Pluto’s size down to a few kilometers, thanks to occultations.” It’s also possible to learn about a planetary object’s other properties—for instance, whether it has an atmosphere. If a star’s light drops sharply when an object passes in front of it, astronomers predict that the object has no atmosphere. But if the star’s brightness fades more gradually, an atmosphere could be refracting the light.
“The stuff that’s out there is pretty unchanged, preserved from the beginning of the solar system,” Zuluaga says. That means it can provide clues about Earth’s origins.
From his office in the Green Building on campus, Zuluaga uses precise mathematics to predict when occultations will happen, carefully verifying a star’s position in relation to an object’s orbit. With software written by MIT astronomers, he tweaks and refines the probable position of a given star, using the coördinates of others around it for reference. “You use stars whose positions are better known than the one we’re following,” he explains.
The other part of Zuluaga’s job is figuring out the ideal location for an astronomer to observe an occultation. Often, an event might be visible only from, say, New Zealand or Mexico. In these cases, MIT might send a small cadre of observers to use another institution’s telescopes. This year, MIT sent a group of Wallace astronomers to Alaska for the first time: Varuna, an object within the Kuiper Belt of frozen planetary bodies on the fringe of the solar system, was expected to occlude a star. On these expeditions, all the work done to prepare for the trip, refine predictions, and calibrate gear culminates in a crucial half-hour window. “You have to wait for that night to happen,” Brothers says. The bulk of an astronomer’s time is spent preparing to capture a single moment.
Need to develop cloud mover.
—September 23, 1997, 2:30 a.m.
During that brief window, it’s crucial that nothing go wrong. But often, things do: a power failure, a technological glitch, bad weather. Astronomers always have to be prepared for the possibility that an observation will result in no data at all.
Before the trip to Alaska, EAPS PhD candidate Amanda Zangari spent hours testing MIT’s equipment to ensure it would hold up in weather that makes wires freeze and snap in half. She bought a six-pound pair of extreme-cold military boots and made charts to study what the sky would look like from up north.
After a journey marred by a canceled flight and a checked bag of camera equipment that arrived late, Zangari’s computer hard drive wouldn’t start in the cold. She brought it inside to warm up, got the computer going, and was finally ready to observe. But heavy clouds that night made Varuna invisible. Zangari and her colleagues came home empty-handed. There’s a twinge of guilt when that happens, she says, but she’s used to it by now. “The only thing you can do,” she says, “is make sure everything was ready—that you were in the right part of the sky had the stars been available.”
Back at Wallace, in the hours leading up to Quaoar’s occultation, Brothers and Sallum notice a problem with the 16-inch telescope: it’s so cold that the shutter in the camera has frozen shut. They wipe off condensation and plug in heated Velcro straps known as dew heaters to warm the camera. Nothing works.
Sallum, an EAPS major, has never seen an occultation before. She has driven out from campus with two friends (engineering majors who have since fallen asleep in the bunk room) and is crossing her fingers that she’ll get to see results.
But equipment is in short supply. It’s the same week as the Alaska trip, and Brothers has sent the observatory’s more advanced cameras with the team up north. The shutters of all the remaining high-speed cameras are frozen shut. With an hour to go before the occultation, they need to find another option—fast.
The only other cameras on hand are lower-quality models typically used for introductory astronomy classes. With no time to transfer one of these to the larger telescope, they’ll have to record the occultation from one of the small 14-inch telescopes in the observatory’s teaching shed. “It was a close call,” Brothers says. “We just took a chance.”
Very thin haze apparent from the blurred star images … If the method works as I believe it should, then a search for … amplitude variables among the BO [blue] supergiants in the cluster will be made.
—September 1, 1971, 2:00 a.m.
Since it opened in 1971, the Wallace Observatory has concentrated on both research and teaching. “We depend a lot on student work and time to get our results, and simultaneously we’re teaching them how to do the research,” explains Michael Person ‘94, SM ‘01, PhD ‘06, the observatory’s associate director. “Jim Elliot was long a supporter to students involved in research,” Person says of the observatory’s revered director James Elliot ‘65, SM ‘65, who led the Wallace Observatory for more than 30 years before he died in March. “The first thing he wanted me to do upon finishing my PhD work was to set up a large summer program and have half a dozen students out at Wallace every clear night.”
One of Elliot’s major contributions was creating two observing classes at MIT. One class focuses on intensive research, while the other teaches the basics of setting up telescopes. Students start by aligning their telescope with the North Star, then set it up to move in line with Earth’s rotation. They use the camera attached to each telescope to take exposures of the star clusters they see.
The idea of training the next generation of astronomers drove the initial proposal for an MIT observatory. Students had started to develop a keener interest in astronomy in the 1960s, as the Apollo program took off. After Neil Armstrong and Buzz Aldrin, ScD ‘63, walked on the moon in the summer of 1969, enrollment in MIT astronomy courses spiked to 425 in the 1969-‘70 school year, up from only 22 two years earlier. Students had to borrow time on other institutions’ telescopes, resulting in long waiting lists. MIT needed a facility of its own.
At the time, MIT astronomers were already known for their research in radio astronomy. Several faculty members had made key discoveries by studying invisible radiation. In 1955, physics professor Bernard Burke ‘50, PhD ‘53, was part of a team that found radio emissions from Jupiter; in 1962, his colleague Bruno Rossi co-discovered the first source of celestial x-rays. MIT president Howard W. Johnson saw “excellent potential” for the school to make similar strides in optical astronomy.
Once the idea of an astrophysical observatory gained support, the observatory itself needed a site. However, not just any land would do. It had to be near a major highway for easy access, far enough from city lights to provide a dark night sky for observing, and preferably far enough inland to avoid the characteristic Boston fog. After rejecting potential sites in Boston Harbor, New Hampshire, and Connecticut, the planning committee chose Westford, near MIT’s radio observatory on Haystack Mountain.
George Rodney Wallace Jr. ‘13, a resident of neighboring Fitchburg, offered to foot much of the nearly $400,000 construction cost. A paper-company president who’d been educated in chemical engineering, Wallace collected antique cars—and happened to love astronomy. He was 82 when the George R. Wallace Jr. Astrophysical Observatory was dedicated in the fall of 1971.
Since the last time anyone wrote here, Pluto’s atmosphere was discovered by … Jim Elliot ‘65, and the Sox have blown another world series (that was ‘86).
—July 15, 1989 (after a three-year hiatus in entries)
In Wallace’s four decades of operation, scientists trained there have achieved several firsts, including the first accurately predicted and observed occultation of a Kuiper Belt object (other than Pluto).
Brothers and Sallum are aiming for another first with the Quaoar observation. A half hour before the occultation, they evaluate their telescope’s angle, trying to match the section of sky it captures with the coördinates Quaoar will cross. It is, as Sallum calls it, a pulse-quickening experience. They have trouble identifying the field; Sallum is still looking for patterns she recognizes at 4:45. When the clock reads 4:50—13 minutes to go—they take a leap of faith. They realize that they are just going to have to start.
Once observers at Wallace position the telescope and program the camera, they can see the stream of live images from a computer indoors. With freezing fingers, Brothers and Sallum position the telescope and connect it to the camera, which they’ve already programmed to take an exposure every 10 seconds. Then they hurry in to watch.
Inside, the atmosphere is “pretty tense,” according to Sallum. At 5:02, they begin watching carefully. The occultation is predicted to happen at 5:03, but 60 seconds tick by with no activity on the screen. Maybe the telescope isn’t aligned properly after all. Brothers and Sallum keep their eyes on the star, sip hot drinks, and watch for any sign that it is fading.
At 5:04, the star disappears. Ten seconds later, it is back, dim and shadowy. Sallum holds her breath. Ten seconds after that, the star is bright again.
But Brothers and Sallum aren’t ready to declare victory just yet. “We were both pretty excited, but after having such a terrible night with equipment, we didn’t want to jump the gun and think we had actually seen it before we knew,” Sallum will later recount.
As they drive back to Boston at sunup, Sallum is hopeful. It will take a few days to analyze the star’s light curves and determine whether she and Brothers had really seen the occultation. As it turns out, their instincts were right: Quaoar had occulted a star, and Brothers and Sallum had caught it on camera.
1st Quaoar occultation ever!
—February 11, 2011
Researchers at Wallace are especially proud to have made such an important discovery from a relatively small teaching facility. After all, other observatories boast much more impressive instruments: the mirrors of the European Southern Observatory’s Very Large Telescope (VLT) in Chile are about 13 times the size of those on Wallace’s biggest telescope.
“We got the first occultation data of this object on home turf,” Person says, adding that the researchers presented their findings at this year’s American Astronomical Society meeting. “One of the tributes to Wallace is that we can do serious science with modest means and smaller equipment.”
The equipment at Wallace may be modest by today’s standards, but it is a remarkable improvement over what the facility started with. In 1971, computerized controls were considered revolutionary. Indeed, the computer controlling Wallace’s 24-inch telescope made it 10 times as efficient at precise tracking as manually guided telescopes. The planning committee wrote that thanks to this technology, the observatory would “rank among the most modern facilities of its type anywhere in the world.”
Since then, the computer equipment has become much smaller and more reliable. Last winter, scientists at Wallace engineered new robotic controls for the large telescope. The new system will allow the telescope to self-correct and track the movement of a planetary object virtually independently. “This will really bring us into the current century,” says Brothers. The system also allows for longer exposures, letting in more light and providing clearer data.
—December 2, 1997, 8:45 p.m.
—December 2, 1997, 11:30 p.m.
Some things haven’t changed—like the humor and camaraderie that come with working in the middle of the night. And the practice of astronomy continues to be subject to random luck. In May, researchers who tried to spot a Pluto occultation from Wallace were thwarted by storm clouds. But groups in clear-skied Vermont and Maryland got a good look.
“The event did happen, pretty much where we predicted,” Brothers says. That’s a triumph in itself, he explains: “It’s very important that we know our predictions are accurate.”
It’s especially important because Brothers, Person, and other MIT astronomers travel as far as Thailand and Australia on the strength of their predictions—and access to larger telescopes for important events hinges on their accuracy as well. Several groups are usually competing for the same telescopes in the same areas on the same nights; it’s important to submit accurate proposals to have a chance. “We try to keep on top of events. It’s a very cutthroat business,” says Zuluaga, half joking. He looks a year in advance to determine which occultations will be worth pursuing. There’s “almost a little common pride” in securing a good telescope for a major event, he says. Having their own observatory in Westford proves a great advantage for events observable from New England.
The Wallace Observatory was originally intended to last 50 years, but as it turns 40, it shows no signs that its time is almost up. “We’ve got new equipment, more control systems, and we’re starting to get even more interest in classes,” Brothers says. The plan, says Person, is to keep expanding and growing past the life span originally imagined. “We’re not starting any 10-year countdown to the end,” he says. As telescopes are refurbished, cameras are improved, and important findings keep coming, Wallace remains a leader in student astronomy research. As Brothers puts it, “I think we have a hidden gem out here.”
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