TIME: Almanac 1993/TIME Almanac 1993.iso/time/072291/0722300.000

Text File | 1992-08-28 | 7.7 KB | 163 lines

                                                                                SCIENCE, Page 52

The Double Dawn


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?