'COME see the light show that only one person in a thousand ever sees!" beckoned Mexican tour guides and Hawaiian trip brochures. "A once-in-a-lifetime opportunity!"This light show - a total solar eclipse - has been dubbed the "eclipse of the century." Flights to the vacation resorts, which offer the best eclipse viewing, have been booked solid for months. Parades, concerts, and even special breakfast menus and hairstyles have been planned. The sun and moon will line up over the earth just after sunrise on July 11 in the middle of the Pacific Ocean. The moon will completely block light from the sun, creating a 160-mile wide lunar shadow that will glide 9,300 miles over Hawaii, through Mexico and Central and South America, to the east coast of Brazil. [See diagram for path of shadow.] "It's the most gorgeous sight anyone has seen on Earth," says Jay Pasachoff, professor of astronomy at Williams College, in Williamstown, Mass. "It's easy to understand why ancient people were so frightened when the sky got dark as night when it was suppose to be light outside. "I saw my first eclipse in a plane over Boston when I was a freshman at Harvard," Dr. Pasachoff says. "My professor, Dr. Donald Menzel, took the entire class up to see it. I was so impressed that I'm still studying them 32 years later." A total solar eclipse occurs somewhere in the world every two years or so. But the one this year has eclipse watchers especially excited. "This is one of the few times this century that an eclipse is occurring directly over a major observatory [the Mauna Kea Observatory on Mauna Kea, Hawaii]," says Kenneth Brecher, a professor of astronomy and physics at Boston University. The observatory, which has the most powerful telescopes in the world, is in the path of the umbra, the band of total darkness. "The fact that it is going directly over Mauna Kea means we can observe the outer atmosphere of the sun at higher magnification and with more sophisticated detectors than ever before," says Robert McLaren, associate director of the Institute of Astronomy of the University of Hawaii, manager of the Mauna Kea Observatory. "We've got the best equipment at the best site," he says. "This event is unprecedented.... An opportunity like this [direct observation over this observatory] may not happen again for centuries, statistically, not for another 400 years." The total eclipse will be visible for a maximum of 4 minutes and 12 seconds in Hawaii, a long time by eclipse standards. Visibility typically lasts only two or three minutes. Scientists started competing for a place at Mauna Kea's specialized telescopes two years ago because study space was so limited, Dr. McLaren says. Though tight, it wasn't impossible to get a reservation. "Solar astronomy is a specialized faction of astronomy," McLaren says. "The number of scientists actually involved in this is rather small." Almost all of the experiments chosen for study in Hawaii involve the sun's corona, the mysterious outer atmosphere of the sun that appears as a fiery white halo around the moon during the eclipse. "The corona remains a mystery because the brightness of the inner sun makes it too faint to be seen against the blue sky," says Pasachoff, who is one of the scientists traveling to Hawaii. "We have to wait for an eclipse to study it." "The corona has scientists baffled because it is the outermost atmosphere of the sun," he says. "Yet it is up to 1 million degrees hotter than the sun's surface, and no one knows why." The study of the corona is particularly important because the data could lead to a better understanding of why the sun shines and may eventually help in the production of controlled fusion on Earth, Pasachoff says. "The corona is made of hot gas held in place by the sun's magnetic field," he continues. "Scientists on earth are trying to use magnetic fields to hold hot gases in place long enough for fusion to take place, but so far have been unsuccessful." By using the sun as a distant laboratory, a better understanding of the laws of physics governing hot gases in magnetic fields may help scientists produce fusion on Earth. Groups of astronomers are also gathering in Baja California, where totality will last two minutes longer than in Hawaii. Willet Beavers, staff member of the Massachusetts Institute of Technology's Lincoln Laboratory, in Lexington, Mass., will try to determine the "life history" of cosmic dust from Mexico's peninsula. Dust left over from the formation of the solar system, particles from comets, and other solar system residue are floating in space around the sun. "This dust, like the planets, is pulled into the sun by its [the sun's] gravitational force," Dr. Beavers says. "We want to determine the dust's ultimate fate - does it vaporize from the extreme heat of the sun, or pile up and stay in orbit?" Beavers and a team of astrophysicists from Iowa State University will identify the dust's movement through space by watching sunlight reflect off the dust particles. Other scientists are using the darkness created by the eclipse to study the area around the sun. "Our experiment is unusual because we are mainly studying solar system phenomena to try to find a permanent feature that we haven't seen before," Boston University's Dr. Brecher says. This project, aimed at finding a ring around the sun, is headed by Dr. Giovanni Fazio of the Smithsonian Astrophysical Observatory, in Cambridge, Mass. "A ring was found around Jupiter by Voyager in 1979. Two years earlier, a ring was found around Uranus. We've known for 300 years there is a ring around Saturn. Why not one around the sun?" Brecher asks. Most people in the Western Hemisphere will be outside the path of the umbra, and will see only a partial eclipse. People living in Los Angeles, for example, will see the sun only 69 percent covered. Wherever eclipse watchers are, they should never look directly at the sun unless at the moment of totality. Instead, they should watch the eclipse in the changing shape of the sunlight on the ground, says Sherwood Harrington, chairman of the astronomy department at DeAnza College in Cupertino, Calif. The spots of sunlight shining through leaves onto the ground or walls of buildings are the shape of the sun. During an eclipse, the circles "look like a cookie with a bite out of it," Dr. Harrington says. The cookie becomes whole again as the moon moves away from the sun. Other phenomena to be on the lookout for during any total eclipse are Baily's Beads and shadow bands, Harrington says. As the moon covers more of the sun, the light of the sun streams through the moon's hills and valleys and appears as beads of light here on Earth. "Then, just a minute or two before totality, those in the path of the shadow will witness shadow bands," Harrington says. "People will see shimmering waves of light moving past them," Brecher says. These will look like the light and dark bands one sees at the bottom of a swimming pool as a result of the water diffusing the sunlight. "The atmosphere is acting like the top of the water and we are at the bottom of the pool," Brecher says. "It's a spectacular sight," Harrington says. "This is why people spend thousands of dollars to go all over the world to see one of these things." "I don't understand why everyone doesn't want to go," Pasachoff says.
PEAK ECLIPSE VIEWING TIMES PARTIAL ECLIPSES: City Time Alanta 3:31 p.m. Chicago 2:16 p.m. Denver 12:50 p.m. Honolulu 7:29 a.m. Houston 2:18 p.m. Kansas City 2:08 p.m. Los Angeles 11:27 a.m. Miami 3:49 p.m. Minneapolis 2:04 p.m. New York 3:34 p.m. Salt Lake City 2:38 p.m. San Francisco 11:20 a.m. Seattle 11:22 a.m. Toronto 3:24 p.m. Tucson 11:43 a.m. Vancouver 11:22 a.m. Washington 3:33 p.m.
TOTAL ECLIPSES: Hilo, Hawaii 7:30 a.m. Mexico City 1:24 p.m.
All times in the local time zone. (Source: Astronomy magazine/eclipse press kit)