Sky Spectacular

Few areas of North America are more isolated or serene than Mexico's Oaxaca state, astride the Isthmus of Tehuantepec. Foreign visitors are few, and they are usually young Americans interested in eating local "magic" mushrooms. Yet for the past few weeks, Oaxaca (pronounced wa-hac-a) has been bustling with unnatural activity. Toting tons of expensive paraphernalia, nearly 800 scientists from 14 countries have descended on the mountainous state. Frightened by the "demon" that the scientists have come to see, superstitious Indian villagers have been busily offering prayers, lighting candles and staging other rituals. Their supplications are designed to keep the demon at a distance. But they are not likely to succeed. On the morning of Saturday, March 7, the sun will temporarily vanish from the skies of Oaxaca, blotted out by a total solar eclipse.

Oaxaca lies directly in the path of the narrow, 100-mile-wide shadow that will be cast by the moon as it moves directly between earth and sun. If the usual cloud-free weather prevails, the remote area will offer astronomers a ringside seat for the sky spectacular. As the moon's shadow sweeps northward, millions of Americans and Canadians may also be able to catch a glimpse of a total or nearly-total eclipse, although direct observation can be highly dangerous (see box). The path of totality extends across the Gulf of Mexico, cuts through Florida, Georgia and the Carolinas, brushes past Virginia and New England, and finally disappears at sea beyond Newfoundland and Labrador. Viewers as far away as San Francisco may have an opportunity to see part of what some overly exuberant sky watchers have already dubbed "the eclipse of the century."

Perverse Habit. Actually, solar eclipses are fairly common. As many as five can occur in a single year, although they invariably last no more than a few minutes and often frustrate astronomers by what Veteran Eclipse Watcher Donald H. Menzel of Harvard calls their "perverse habit of hitting desolate regions." Because of its favorable viewing path and timing--near the peak of the sun's eleven-year sunspot cycle--the March 7 eclipse is being eagerly awaited by astronomers.

Millions of dollars have been spent on preparations for what may well be the most intensely observed eclipse in history. Besides the numerous telescopes, cameras and other elaborate gear located in Oaxaca, other equipment is being set up at observatories all along the Eastern Seaboard. By the fortunes of celestial mechanics, the eclipse's path will cross Wallop's Island, Va., where NASA scientists will send up 33 probing rockets as the shadow approaches. In addition, several research planes will seek an above-the-weather look at the eclipse; a U.S. Air Force KC-135 will even race the moon's shadow in order to get a few precious extra moments of observation time.

Scientists will study the sun's corona with particular interest. Fully visible only during an eclipse, the glowing halo offers important clues to the powerful energy processes at work inside the sun. Repeating other experiments that are only possible when the sun's rays are shielded by the moon, the researchers will search for nearby comets, study interplanetary dust and conduct an Einsteinian relativity test--measuring the deflection of starlight by the sun's powerful gravity. They will even look again for the legendary planet Vulcan, which has never been observed since a French astronomer reported "seeing" it between Mercury and the sun in 1859.

Shock Waves. More than half of the 100 major experiments, however, will involve the earth and its atmosphere. Boston College Meteorologist Edward Brooks, for example, will study the processes of cloud formation; some scientists contend that it should be abetted by the cooling effect of an eclipse. If this happens, earthbound observers may get a grandstand view. On radio command from the ground, the U.S. Applications Technology Satellite (ATS-3) has been temporarily moved in its equatorial orbit from a position over eastern Brazil to one with a better view of the path of the eclipse. If all goes well, the Weather Bureau says, satellite pictures of the eclipse's effects on the cloud cover can be shown that night on TV.

A few of the experiments are even more esoteric. As the moon's cooling shadow crosses the earth, say University of Toronto Physicists C.O. Hines and G. Chimonas, it may set off low-frequency atmospheric shock waves. To test their theory, some 50 observers scattered across the country will attempt to "listen" to the faint rumbling with extremely sensitive instruments called microbarographs. Other scientists will listen to more familiar noises. In Georgia's Okefenokee Swamp, a team of animal behaviorists will attempt to learn whether the swamp's creatures will be so confused by the temporary darkness that they begin to emit night calls.

If scientists are enthusiastic, so are ordinary citizens. Last week a woman called New York's Hayden Planetarium and asked whether tickets were being sold for the eclipse. "No," replied Astronomer Kenneth Franklin, "it's being handled by an Independent Producer."

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