Total Eclipse May Help Solve Mystery of Sun's "Halo"

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"Leon makes the most fantastically detailed x-ray pictures of the corona," said Pasachoff. "On his images, you can see loops of gas the size of the Earth. In our experiments, in Africa, we are studying how those loops shake, and whether that shaking heats the corona to millions of degrees."

Golub and Pasachoff are co-authors of a new book about the sun: "Nearest Star: The Exciting Science of Our Sun," which has just been published by Harvard University Press.

At Pasachoff's site in Lusaka, Zambia, the total eclipse will last 3 minutes, 14 seconds. This period of total coverage of the sun by the moon will begin at about 9:09 U.S. Eastern Time (the local time in Zambia is six hours ahead of this.)

Pasachoff's team is collaborating with scientists from Zambia, England, Slovakia, Indonesia, and India—and with the students from Williams College. "It's fun to be here with so many students," he said. "It is exciting for them and for me to have a chance to work in a foreign place and to anticipate the drama of the eclipse."

Two of the Williams College experiments in Zambia deal with the still-open question of how the corona can reach a temperature of millions of degrees, even though the everyday surface of the sun below it is only 6,000 degrees Celsius (about 11,000 degrees Fahrenheit).

Part of these experiments and a third experiment are being done in liaison with scientists conducting experiments on the Solar and Heliospheric Observatory (SOHO) spacecraft and the Transition Region and Coronal Explorer (TRACE) spacecraft.

Targeting the Corona

The Williams College team's first experiment is a search for rapid vibrations in the corona. A theory holds that extreme coronal heating is caused by loops of gas held in place by the sun's magnetic field. The question is whether the vibrations bring enough energy into the corona to heat it sufficiently.

The second experiment involves making a map of the temperature and polarization of the corona, using a technique of comparing electronic images of the corona taken at special ultraviolet wavelengths. Following theoretical work, these wavelengths are chosen to include two at which the difference between the shape of the everyday sun's spectrum and the corona's spectrum is especially striking.

The third experiment is to image the solar corona during the eclipse to compare with observations of the corona seen with the Extreme-ultraviolet Imaging Telescope (EIT) on board the SOHO, in collaboration with scientists at NASA's Goddard Space Flight Center and from the U.S. Naval Research Laboratories.

"We are all geared up and ready to go," said Pasachoff. "Our two tons of equipment arrived safely, and we have spent two weeks testing it and making sure it tracks the sun exactly across the sky. Everything is working well, and we hope for continued clear skies on Thursday afternoon."

Pasachoff filed a dispatch after his team observed the eclipse in Zambia on June 21: The weather was clear and the team gathered a lot of data. It was, he said, a "Spectacular Show." Go>>

Watch tonight's broadcast of National Geographic Today on cable television in the United States at 7 p.m. ET/PT for video of the eclipse.

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