TIME: Almanac 1995

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<text id=91TT1620> <title> July 22, 1991: The Double Dawn </title> <history> TIME--The Weekly Newsmagazine--1991 July 22, 1991 The Colorado </history> <article> <source>Time Magazine</source> <hdr> SCIENCE, Page 52 The Double Dawn </hdr><body> The eclipse taught scientists that the sun is bigger than they had thought, and its atmosphere hotter and denser By Claudia Wallis/Waikoloa--With reporting by Jim Borg/Mauna Kea and Laura Lopez/San Jose del Cabo High on the mountaintop, where the life-giving star is worshiped, no one slept a wink. There in the cold, thin air of Hawaii's Mauna Kea, home to the world's greatest concentration of high-powered telescopes, the scientists paced, fretted and nervously tuned their instruments. Night is darker than pitch at the crest of the 4,300-meter (14,000-ft.) dead volcano. In that utter blackness, the ultimate sun worshipers waited for the day that would dawn not once but twice. By sunrise at 5:52 a.m., a total of 250 scientists, journalists and guests had gathered, waiting and waiting for the last eclipse visible from the U.S. in the 20th century. At 6:30 a.m. the celestial show began. Like a devouring sky god, the moon's shadow appeared, gouging out a perfectly rounded bite from the upper edge of the sun. Moving at 10,000 km/h (6,000 m.p.h.)--but as slowly as a distant airplane to the human eye--the shadow crept down the face of the sun. Soon it obscured all but a thin lower crescent that gleamed against the darkening sky like the Cheshire Cat's smile. Next the corners of the smile vanished, leaving a single dazzling gem of brilliance at the bottom of a circle of light--the so-called diamond-ring effect. At 7:28, the solitaire blinked out. And, as if the hand of God had thrown a switch, day turned to night. Left in the sun's place was a black orb surrounded by a wide, shimmering halo--the solar corona, visible only during an eclipse, when it is not obscured by the sun's bright glare. From the 12 o'clock position, an enormous red-orange flame flared beyond the halo; smaller "prominences" appeared at the 3 and 6 o'clock positions. Murmurs of wonder rose from the shivering crowd draped in the steel-gray light. "Mind blowing," said Edward Kuba, University of Hawaii regent. "Wonderful, wonderful," pronounced Sony chairman Akio Morita, one of several VIPs present, as he gazed through a new video camera from his company. Then, with stunning suddenness, the four minutes of totality ended, another diamond ring appeared, and the shadow of the moon could be seen fleeing across the Pacific toward Baja California. Veteran eclipse watchers who caught the show on July 11, 1991, declared it to be one of unsurpassed beauty. But from the standpoint of science, it was something of a letdown. High, thin clouds made a rare appearance above Mauna Kea that morning, interfering with the quality of data gathered through telescopes. "It was a miserable sky in the infrared," complained astronomer Robert MacQueen. Even more damaging to the infrared readings was the fine dust accumulating in the earth's atmosphere since the June explosion of Mount Pinatubo in the Philippines. "It's just heartbreaking that after being dormant for 600 or 700 years, the volcano didn't wait another week or two before erupting," said Donald Hall, director of the Institute for Astronomy at the University of Hawaii. Still, this was the eclipse that came to the astronomers, the first in modern times to pass directly over a world-class observatory. Despite less than ideal conditions, most of the Mauna Kea scientists were elated by what they had observed. John Jefferies, who helped oversee three separate projects, said the findings would forever change earthlings' view of their star. One of Jefferies' studies showed that the sun is bigger than previously thought. Looking at invisible wavelengths that represent hydrogen emissions, he found that the sun's chromosphere, or lower atmosphere, extends 6,000 km (3,700 miles) beyond what is normally visible. "That is farther out by a considerable distance [0.4%] than the standard models tell us," he said. Other measurements from a prominence indicated that the atmosphere is both hotter and denser than had been imagined. Jefferies was one of many astronomers looking for clues to one of the central mysteries of the sun: Why does the outer atmosphere, or corona, have a temperature (1,000,000 degrees C) so much higher than that of the sun's surface, or photosphere (5,500 degrees C)? The logical expectation would be that the temperature continues to decline as distance increases from the sun's core (15,000,000 degrees C). A leading theory attributes the corona's heat to small-scale explosions called microflares, caused by the sun's powerful magnetic field. Barry LaBonte of the University of Hawaii sought to glimpse these microflares by training his telescope at the inner edge of the corona. When he finishes analyzing his data, he hopes to have evidence of "small explosive events in the corona that basically make it twinkle like a string of firecrackers going off." A second point of fascination for the astronomers is the fate of interplanetary dust, the residue of the creation of the solar system. This dust is drawn in by the sun's gravity and vaporized near the star. Mauna Kea scientists had hoped to study the glow from the vaporization of interplanetary particles, but dust from Mount Pinatubo jeopardized the experiment. "We had hoped that we could quickly process the data and be able to shout `Eureka!' " said Hall. "We are now very uncertain about what we will learn until days or weeks after totality." Far below the mountaintop, on the beaches, tennis courts and roadsides along the western coast of the Big Island of Hawaii, there was more grumbling about the viewing conditions. Some 40,000 tourists had come for what the Hawaii Visitors Bureau had billed as the "most thoroughly anticipated four minutes" in the history of Hawaiian tourism. Some spent the entire night camped out with lawn chairs and tripods set improbably on the rugged brown-black moonscape of Kona's lava flows. Their luck was as dappled as the morning sky. An NBC camera crew, perched on the roof of the Royal Waikoloan Hotel, saw the clouds swallow the sun minutes before totality. A group of 2,000 enthusiasts sponsored by Hawaii's Bishop Museum Planetarium gathered at an elaborately chosen spot and saw nothing. Just 40 km (25 miles) away in Kailua-Kona, the crowd on the luau grounds of the King Kamehameha Hotel was also socked in until a small clearing appeared just two minutes before totality. A cheer went out: "Come on, sun, you can do it, you can do it!" And sure enough, it did. Others caught the moon's shadow in its 15,000-km (9,320-mile) journey across the Pacific to Mexico and eight countries of Central and South America. Perhaps the best viewing site was Baja California, where nary a cloud darkened the vista. In the San Jose del Cabo area, where 35,000 tourists flocked, the temperature dropped from 32 degrees C (90 degrees F) at 10:24 a.m. to 23 degrees C (74 degrees F) when totality occurred 1 hr. 26 min. later. For the ultimate spiritual experience, no site could surpass the ancient Olmec pyramids at Cacaxtla, southeast of Mexico City. There a pallid re-enactment of Aztec dances failed to stir the crowd of 3,000, but the sun's pas de deux with the moon, lasting nearly six minutes--a minute and a half short of the maximum duration possible--led many to fall to their knees. With Mars, Mercury, Venus and Jupiter suddenly bursting into view in the afternoon, what else could they do but give thanks to the gods, ancient and modern, and pray for the opportunity to view the double dawn again in their lifetime? </body></article> </text>