Eclipses Offer Fleeting Chances for Scientists

Aug. 10 —, 2000 -- Dust circling the sun and glowing silicon — these are the some of things scientists look for during a solar eclipse.

Jeff Kuhn, a physicist at the Institute for Astronomy at the University of Hawaii, and his colleagues may have found both during the last solar eclipse.

“We’re seeing some evidence of some kind of emission process, glowing dust, in the plane of the [planets],” Kuhn says. The data could help explain why dust that sweeps in from interstellar space hasn’t gathered in a Saturn-like ring around the sun.

Seeing the Not-So-Bright

Research like this can’t be done on most days.Don’t look at the sun, parents admonish. For scientists interested in the corona, there’s often no point. The sun is so bright that it effectively hides anything nearby within a bath of brilliant sunlight.

When the moon obligingly turns out the main light during a solar eclipse, which happens roughly every 18 months, scientists flock for a chance to gaze for a couple of minutes at the glowing gas and dust that make up the sun’s atmosphere, or corona.

Science by eclipse is much patience followed by a brief flurry of frantic activity.And while the moon’s motions are predictable, weather isn’t. If a bank of clouds rolls over, the effort is wasted, and then it’s another year-and-a-half wait.

Outwitting the Weather

When the last total solar eclipse rolled over the Caribbean in February of last year, Kuhn, then at Michigan State University, figured a way to get above the clouds — a C-130 cargo plane at 18,000 feet.

Flying at 250 mph in the same direction as the shadow extended the darkness to five minutes.

An infrared camera — based on technology from heat-seeking missiles — caught a very specific color of light that would be given off by glowing dust. But the researchers are still sifting through their data. “It’s a tiny signal against the background glare of all the dust that is reflecting sunlight,” Kuhn says.

Seeing a little bit of dust can tell why there isn’t more. “The old picture is that dust from comets, extrasolar space, should accumulate around the sun in a ring,” Kuhn says. “The fact that it doesn’t tells us we don’t really understand where the dust comes from or where it moves in the solar system. It’s being moved around by other forces we hadn’t accounted for”

Electric Dust?

It’s possible, for instance, that the dust particles get charged up with static electricity and then get shoved along by the sun’s magnetic fields. Measurements of the dust density could support or disprove various theories.

The infrared camera also captured light emitted by silicon ions in the corona. By analyzing how the magnetic fields of the corona splits this color into two slightly different shades, the scientists hope to better understand how the fields heat the corona to several million degrees — far hotter than the 11,000 degrees Fahrenheit at the sun’s surface — and accelerate the particles of solar wind that blow out of the sun.

The eclipse camera wasn’t sensitive enough to distinguish the two shades, but the tentative results are enough to motivate building a ground-based infrared telescope in Hawaii for a closer look.

This time around, though, Kuhn will be half a world away, in Hawaii sunshine instead of in the shadow.

“We had really good luck last year in Panama,” he says. “That’s enough to keep us really busy. My cycle time [between eclipses] is three or four years.”