Seasons in the Sun

Behind the wheel of his Cadillac SRX, Edward Rhodes slows to a stop at Big Tujunga Canyon Road, where a crew works on asphalt leading to the Mt. Wilson Observatory.

“We’ll find out right about here whether they’ll let us up the mountain,” says Rhodes, professor of astronomy in USC College.

A crewman signals for him to go around the orange cones. Rhodes sighs with relief. After many attempts, he has finally been given clearance to visit the observatory. He hasn’t done so since the Station fire roared through the Angeles National Forest in summer 2009, forcing evacuations, road closures and halting research at the site’s 60-foot solar tower for two months.

After the roads to Mt. Wilson initially reopened, they closed again in the winter after torrential rains and mudslides hit the Southern California burn areas.

“This drive up the mountain used to be lush and green,” says Rhodes surveying the fire-damaged landscape that looks more like a desert than a forest. “There may be a point further along where they won’t let us up.”

A pioneer in the field of solar physics, Rhodes began conducting research at Mt. Wilson’s 60-foot tower in 1977, as a California Institute of Technology postdoctoral student. In 1984, and now a USC professor, Rhodes became the principal investigator of projects at the 60-foot solar tower, where among other things, daily white-light, megapixel images are taken of the sun’s front hemisphere.

In 1984, Ed Rhodes, professor of astronomy in USC College, became the principal investigator of projects at the 60-foot solar tower at Mt. Wilson Observatory, where among other things, daily white-light, megapixel images are taken of the sun’s front hemisphere. Photo credit Steve Padilla.

The two-month shutdown was the first break in the 25-year data-gathering. The entire observatory was in peril when the largest wildfire in L.A. County history burned through more than 160,000 acres. Flames came close, but did not reach the observatory atop the 5,800 peak in the San Gabriel Mountains. No smoke damage has been detected.

Landmark scientific breakthroughs have occurred at the 102-year-old observatory. It is where astronomer Edwin Hubble discovered there were galaxies beyond the Milky Way in 1925.

Years earlier, scientist George Ellery Hale built a 60-foot tower at Mt. Wilson and in June 1908 used it to become the first to detect the sun’s magnetic fields.

The tower is where Rhodes conducts research with his students, collecting data and studying the sun’s internal structure. A helioseismologist, Rhodes examines the sun’s wave oscillations, similar to how seismologists monitor waves caused by earthquakes to learn about the Earth’s interior.

Rhodes’ group has made its own discoveries. Using the Mt. Wilson Doppler imager, they pinpointed a region of the sun now called the solar subsurface shear layer — a layer just below the sun’s surface where gas moves slower than at mid-latitudes. In a NASA-sponsored project, they are transferring digital images collected since 1988 to USC computer disks, which are being converted to a format widely used in astronomical research exchanges around the world. That data is being archived at Stanford University.

Rhodes examines the sun’s wave oscillations inside Mt. Wilson Observatory’s 60-foot tower, with Taran Huffman, a physics senior (middle), and Shawn Irish, a USC data analyst and daily operator of the tower. Photo credit Pamela J. Johnson.

On this foggy day, Rhodes has brought with him Taran Huffman, a physics senior working part-time at the 60-foot tower.

“One of the benefits of going to USC was I knew that it operated a tower on Mt. Wilson,” Huffman says. “It’s been an excellent opportunity for me as an undergraduate.”

At the tower, Rhodes is greeted by Shawn Irish, a USC data analyst and daily operator of the 60-foot tower. While there, the trio examines negatives of the white-light images.

One research goal is to help determine how much of changing solar activity is affecting the Earth’s climate. The sun can help gauge unusual cold snaps and warming, although, Rhodes emphasizes, “only a fraction” of the current warming is due to solar activity changes.

“We want to better predict what influence the changing level of activity in the sun might have on the Earth, not today, but in the future.”

Read more articles from USC College Magazine’s Spring/Summer 2010 issue.