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The Science of Stargazing
An evening under the night sky
Suprise in the skies: Plesser directs viewers to celestial wonders.
Surprise in the skies: Plesser directs viewers to celestial wonders.
Chris Hildreth

It’s growing dark, and Ronen Plesser can’t find his keys. Eight students wait patiently by a shed next to an open field. Plesser walks the hundred yards back to the parking area, opens all the doors to his SUV, and climbs inside. The light comes on. Time passes. The doors slam shut, and the light goes off. Plesser walks back to the group. He’s moving quickly, muttering to himself; he still can’t find his keys. He bends down to pick up his backpack, and wouldn’t you know it, there they are, right there on the ground.

Plesser, an associate professor of physics and mathematics, may have trouble locating terrestrial objects, but he has no problem finding the stars in the sky: For the past eight years, he’s been running astronomy classes, regular public demonstrations, and other science outreach-education sessions at the Duke Teaching Observatory. The observatory, which opened in 2002, is located on an isolated stretch of road in Duke Forest, and tonight it’s the gathering place for a group organized by the Outpost, a student-affairs organization that loans bikes on campus but also puts together outdoor excursions. The students have signed up for a night of stargazing and are eager to get to the telescope.

Plesser uses his newly recovered keys to open the shed. He pulls out two carts, each wobbling under the weight of a big wooden box. Without explanation, he asks the group to wheel them out to the field.

A narrow path intersects a C-shaped path that runs three-quarters of the way around a grassy level spot. Nine chest-high posts are spaced along its arc. The group lets out a number of variations on “that’s it?” Apparently, when the idea of an astronomical observatory enters the mind of a student these days, visions of a silo-like bright-white behemoth are what they see. “It doesn’t look like Mount Palomar,” Plesser says, referring to Cal-Tech’s now-iconic observatory near San Diego. The telescopes there feed into a computer screen, he explains, adding in a jocular but paternal tone (he is the father of five), “You want to look at a monitor? You can do that in your dorm room!”

The telescopes—they’re the things being lugged on the carts—are fitted on top of the posts. Plesser sets up two of them for the evening’s viewing. It’s three nights before a full moon, so the sky is bright, meaning it will be harder to see fainter stars, but the lunar surface will be easy to see. The telescopes, which weigh about eighty pounds each, are computer-aided, and they take a few minutes to boot up. While this is happening, Plesser points out Cassiopeia. From there, he points left and then straight up: Polaris—the North Star—the fixed point in the sky of the northern hemisphere and the tip of the handle on the Little Dipper.

He moves on to the Autumn Triangle, visible directly overhead. One of the stars in the triangle, Deneb, forms the tail end of the constellation Cygnus, the swan. Plesser says this is his favorite constellation because he can make out its shape so easily

Plesser, who has taught at Duke for thirteen years, didn’t start out as an astronomer, and professionally, he still isn’t—the university does not have a dedicated professor of astronomy or astrophysics. He studies string theory. But while bringing up his children, he gave the occasional educational demonstration in their elementary-school classes. He noticed that the cosmos, which had always fascinated him, was the best, and most immediate, way to get kids interested in science.

One thing led to another, and soon he was leading school groups up the stairs of the physics building to use the rooftop telescopes there. But the increase in use, along with expansion at the medical center that made it harder to see the stars at night, led Plesser, in partnership with administrators, to create the observatory space.

Back in the field, the students are looking through the telescope at Albireo, a binary star. To the naked eye, it appears to be one entity, but with magnification, two stars are clearly visible. One is bright yellow, the other a faint blue. This leads to a discussion of what space is made of. Plesser explains that it is mostly a void, but that stars consist of about 90 percent hydrogen. More questions follow, and Plesser asks whether the students are sure they want to hear the whole story. They do, and so he launches into the Big Bang theory, talking about cosmic dust, the ever-expanding universe, dark matter, supernovas, gamma rays….

“My mind is blown,” says one student. Plesser points the telescope at a ring nebula, which the students can barely make out, and then at the Hercules Globular Cluster, a grouping of hundreds of thousands of stars in the spherical halo of our galaxy, approximately 25,000 light years away. The students visit the telescope one by one. “Ooohhh!”

Next up is Jupiter. The galaxy’s biggest gas giant lost one of its two telltale bands in May, after a climatic event. Tonight, all four moons—Callisto, Europa, Ganymede, and Io, which were first sighted by Galileo and originally designated the Medicean Stars, in honor of his patrons, the Medicis—are visible. They are arranged in what appears to be a straight line, two on either side of the planet.

Plesser redirects the telescope. “What’s that?” a student asks.

“That blue thing?” Plesser answers.

“Yeah.”

“That’s Uranus.”

Although smaller than Jupiter, it is still vivid—and a bright pastel blue.

Plesser has written a couple of primary-school science curricula that incorporate astronomy, and he seems to relish teaching about the stars to students of all ages. An adult amateur astronomy group from Chapel Hill also makes use of the observatory, and, at times, Plesser has devoted as much as 30 percent of his waking hours to coordinating visits and serving as on-site instructor. The immediacy of the experience stokes a curiosity in almost all observers that is fundamental to science, he says. “It shows that the world is worth trying to comprehend.”

During the winter months, when Plesser teaches Physics 55—he calls it “astronomy for poets”—teacher and students are able to form a stronger bond. “We have a great relationship precisely because we’re all out there freezing our butts off,” he says, only half joking.

It’s warm on this late-summer night, three nights before the autumnal equinox. After an hour and a half of standing in the middle of a field, the students are beginning to fidget; they discuss homework and answer cell-phone calls. Plesser fixes the telescope on the moon, our nearest celestial neighbor. Unlike the distant faint stars, it fills the eyepiece with an overwhelming brightness. Tycho, one of its vast craters—nearly 53 miles in diameter with walls more than two miles high—is visible in high relief. The students waiting for their turn hover eagerly. Plesser points out the Sea of Tranquility, the site of the first moon landing. “Ooohhh!”

Clouds begin to roll in, and Plesser decides tonight’s session has come to an end. “This is the universe’s way of telling me it’s time to go home and have dinner,” he says. It’s nearly ten o’clock. Plesser packs up and, keys in hand, locks the telescopes in the shed. He drives the students out of the forest and back to campus.

Aaron Kirschenfeld