Following Hubble's footsteps

By Jennifer Vanasco
News Office

Up a narrow, twisting staircase in Kersten Physics Teaching Center, in a small, dark, circular room, six undergraduates huddle together for warmth.

But once astrophysicist Richard Kron starts giving gentle directions, everything changes. The students move into action, forgetting the cold. They pull covers off the Dunham Telescope, turn on three computers, set a clock to the automated voice that announces Coordinated Universal Time from a shortwave radio receiver. They open the dome of the observatory and direct the telescope to a star they will use to fine-tune their position.

If not the method, students in this Core astrophysics class hope to recreate the results of Edwin Hubble's famous experiments, proving the universe is expanding.

"I chose this class because it was hands-on. We focus on concrete questions step-by-step," said Nancy Dorn, a senior concentrating in art. "What we learn in lecture we do in lab. It's really exciting."

Dorn, like all students taking the 118-119-120 astrophysics sequence for non-science majors, had the choice of continuing the sequence with the standard third-quarter astrophysics class, 120, which normally has 90 students--or taking 122, which is Kron's smaller, lab-focused class.

"With a smaller number of students, we can use our telescopes, computers and the spectrograph to measure the expansion of the universe instead of just talking about it," said Kron, Professor in Astronomy & Astrophysics.

The idea of offering a small astrophysics class came from Peter Vandervoort, Professor in Astronomy & Astrophysics. Vandervoort conceived of and taught 122 as a small lecture class, and now under Kron's direction, it has evolved into a course that focuses on practical astrophysics.

"In this class, we are able to do real astronomy for the first time--and maybe the only time," said Stefan Pedatella, a senior concentrating in English.

The 22 students in Kron's class are divided into four lab groups. Each group trudges up the stairs one night a week to use the telescope mounted on top of Kersten Physics Teaching Center. The Dunham Telescope features an unusual mechanical design called an altitude-altitude mount. "Most small telescopes require you to drag other attached equipment around as the telescope moves," Kron said. "Ours is able to have this huge, harpsichord-shaped spectrograph attached to it without needing to shift the spectrograph around."

A spectrograph splits light from stars and planets into wavelengths. Kron retrofitted the one in Kersten with a new optical arrangement so that it can better measure light from galaxies, which are large and low contrast compared to stars, which are small and high contrast.

In the 1920s, Hubble used data from a spectrograph to show distances between galaxies are proportional to their redshift, a theory that helped prove space is expanding and led to the Big Bang theory of the creation of the universe. Astrophysicists can approximate how long ago the Big Bang occurred by calculating the rate at which galaxies are moving away from each other.

The instruments Kron's class is using are 100 times more sensitive than the ones used in Hubble's time, but "the sky is also about 100 times brighter," Kron said, "so they sort of cancel each other out. It's still very challenging."

He added, "It seems completely hopeless to do astronomy in the city because of all the light pollution. But in this experiment we are concentrating in the red part of the spectrum, and those red wavelengths are not blocked by the city's yellow lights."

The students have been involved in every part of the process. Collectively, they decided to look for galaxies that had supernovas sometime in the past, because the supernovas would provide a benchmark for estimating the galaxies' distances. They also wanted galaxies that were known to have intensely bright hydrogen alpha emission, which is in the red part of the spectrum, so they could be seen more easily by the spectrograph.

The galaxy these students are looking at this evening is M66, near the bright Virgo cluster of galaxies. The galaxy is too faint to see by eye, so they find it by using a sensitive electronic camera on the side of the main telescope. The room is silent with expectation as two students type in commands to the computer attached to the spectrograph. "Everyone's been waiting for this part," Dorn says quietly, "to feel like we're finding out for the first time how the universe began."

The spectrograph shows M66 as a band of bright light. "I believe we have a galaxy," Kron says, and the students spontaneously cheer.

In future labs, they will study other galaxies, collecting more redshift results, and on cloudy days, they will plot the intensity of the amount of light detected at different wavelengths. In the end, they will show, once again, that galaxies are moving apart.

"As far as I know, no other urban university is doing this kind of thing," Kron said. "We're confronting students with physical phenomena directly, and they can't get this experience any place else."

"It's nice," said Angie Brehmer, a junior concentrating in political science. "I feel like we're actually getting somewhere, we're really doing it ourselves."