TIME: Almanac 1993/TIME Almanac 1993.iso/time/070389/07038900.035

Text File | 1992-09-23 | 14.9 KB | 295 lines

                K/                                                                SCIENCE, Page  46

COVER STORY

Fury on The Sun


Once worshiped as a god, earth's star is revealing the secrets
of its awesome power

By  LEON JAROFF


    Strolling outside Arizona's Kitt Peak National Observatory
during a work break, staff observer Paul Avellar at first
thought the angry red glow in the night sky was caused by
forest fires. Then, seeing a greenish fringe and vertical
streamers stretching like ribbons above the horizon, he realized
what was happening. He raced to a telephone and called his wife
and friends, awakening them and insisting they share the view.
"A chance like this doesn't come along very often," says
Avellar. "To see the northern lights is very humbling and
awe-inspiring. You realize the sun is just going about its
business and making our nighttime sky glow without any trouble
at all. It makes you wonder what would happen if the sun ever
really got mad."

    Some 93 million miles away, the sun was, at the very least,
agitated. In early March, an area of sunspots large enough to
contain 70 earth-size planets had come into view around the
eastern rim* of the glowing orb. Created by intense magnetic
fields and cooler than the surrounding gases, the sunspots were
visible as dark blemishes on the fiery surface. Just as
astronomers were turning their attention to the mottled region, a
bright spot suddenly appeared in its midst. It spread like a
prairie wildfire, glowing white hot on the sun's yellow face
and quickly expanding to cover hundreds of thousands of square
miles. The monster blotch was an unusually large solar flare, a
stupendous explosion that belched radiation and billions of tons
of matter far into space.


    The great flare, and its coterie of sunspots, was an
unmistakable signal. It heralded the imminent arrival of the
solar maximum: the period every eleven years or so when the sun
reaches its peak levels of activity and pointedly reminds earth
dwellers of its awesome power. At maximum, the sun bombards the
planet with radiation and particles, causing unusually
brilliant auroras, communications blackouts and power failures.
But it also gives scientists a fresh opportunity to solve some
of the mysteries surrounding the star that provides the earth
with energy, drives the weather and sustains life itself.

    During a maximum, marked by a jump in the number of sunspots
and flares, giant loops of incandescent gases, called
prominences, proliferate, shooting tens of thousands of miles
above the solar surface, sometimes hanging suspended for
months. The solar corona, the halo around the sun visible during
total eclipses, becomes fuller and brighter; great blobs of the
corona, containing billions of tons of hot gas, occasionally
burst free, shooting into space at speeds as high as 2 million
m.p.h. And the earth's upper atmosphere, pummeled by solar
particles, is laced by electrical currents of as much as a
million amperes. These in turn create powerful magnetic fields
that raise havoc below.

    Because the previous maximum occurred in late 1979,
astronomers had targeted 1991 as the year when solar frenzy
would again peak. But the sun is notably capricious. While the
intervals between maximums average eleven years, some have been
as short as seven, others as long as 17. Ever since the sun
began revving up three years ago toward the next maximum, its
activity has mounted with unprecedented speed.

    "It is the fastest riser on record," says Ron Moore, an
astronomer at NASA's Marshall Space Flight Center in Huntsville,
Ala. So fast, in fact, that astronomers are betting on 1990 or
perhaps even later this year, instead of 1991, as the beginning
of the maximum. And what a maximum it could be. Despite the
ferocity of the March flares, Moore warns, "this cycle is still
in its early phase. It's got quite a way to go." Solar buffs are
speculating it might approach the violence reached by the
1957-58 maximum, which touched off five disruptive geomagnetic
superstorms and vivid auroral displays. Says astronomer Donald
Neidig at the National Solar Observatory outpost on Sacramento
Peak, near Sunspot, N. Mex.: "We can't rule out a record
breaker."

    In anticipation of the fireworks, astronomers scheduled a
two-week, worldwide solar-observation period during the second
half of June. The project was timed to benefit from the
observations of the Solar Maximum Mission satellite (nicknamed
Solar Max) before it plunges to its death. Lofted into earth
orbit in 1980 to monitor the sun's activity, the satellite is
gradually descending and will probably re-enter the earth's
atmosphere in November and be incinerated. Solar Max's readings
of the sun's activity were coordinated with observations made
all over the world by ground-based telescopes and instruments
mounted on high-flying rockets. A hundred solar centers around
the globe were linked by an electronic-mail network designed to
provide the latest data on the sun's behavior.

    A major goal of the project was to catch a flare in the act,
mapping all the solar high jinks associated with it from
beginning to end. The sun's timing could not have been better.
During the first week of observations, it set off several large
flares and ejected billions of tons of matter in a prominence
that extended more than 200,000 miles into space.

    The intense solar observations should provide clues to many
of the still unanswered or only partly resolved questions about
the sun: Does the solar cycle affect terrestrial weather? What
internal mechanisms control the cycle? Is the sun growing
cooler? Hotter? Is there a basic flaw in the current theory
about the fusion process that powers the solar furnace?

    While the recent flares did not measure up to the March
conflagration, astronomers were jubilant. "We have been
exceptionally lucky," says Alan Kiplinger, a solar physicist at
the University of Colorado. "It's unusual to have the sun
cooperate."


    Fortunately for earth dwellers, the March flare occurred on
the easternmost edge of the sun and thus aimed its full force
away from the earth. But on March 10, when the sun's stately
rotation brought the turbulent group of sunspots to a position
more directly facing the earth, a second, only slightly less
powerful flare erupted in the region. Eight minutes later,
traveling at the speed of light, a blast of X ray and
ultraviolet radiation seared the earth's upper atmosphere.
Within an hour, high-energy protons began to arrive, followed in
three days by a massive bombardment of lower-energy protons and
electrons.

    Among the first to feel the effects of the flare's fury was
the orbiting Solar Max. As the radiation saturated Solar Max's
instruments, a NASA spokesman reported, "the satellite was
stunned for a minute and then recovered." Heated by the
incoming blast of radiation, the upper fringe of the atmosphere
expanded farther into space. Low-orbiting satellites,
encountering that fringe and running into increasing drag,
slowed and dropped into still lower orbits. A secret Defense
Department satellite began a premature and fatal tumble, and the
tracking system that keeps exact tabs on some 19,000 objects in
earth orbit briefly lost track of 11,000 of them. Solar Max
descended by as much as half a mile in a single day, almost
certainly hastening its demise.

    On the earth, the flare's effects were equally disruptive.
Shortwave transmissions were interrupted, some for as long as 24
hours, and satellite communication and a Coast Guard loran
navigation system were temporarily overwhelmed. Powerful
transient magnetic fields, generated in the upper atmosphere by
the flare, induced electrical currents in transmission lines
and wiring, and mystified homeowners reported automatic garage
doors opening and closing on their own. A surge of
flare-induced current was blamed by Hydro-Quebec officials for
shutting down the power company's system and blacking out parts
of Montreal and the province of Quebec for as long as nine
hours. These startling phenomena were shrugged off by Sacramento
Peak's Neidig. "A really big flare," he says, "can produce
enough energy to supply a major city with electricity for 200
million years."

    By far the most dramatic manifestation of the solar flare
was the two-night, spectacular display of the aurora borealis,
or northern lights, that awed Paul Avellar and millions of
others. Arriving high-energy electrons, deflected by the
earth's magnetic field, spilled into the upper atmosphere near
the north and south polar regions, which are unprotected by
magnetic-field lines. Acting much as does the electrical current
in a neon sign, the electrons banged into oxygen atoms, causing
them to emit red and green light.

    Ordinarily far less intense and visible only in arctic
climes, the glowing, flickering aurora was seen as far south as
Brownsville, Texas, and Key West, Fla. Alarmed Floridians,
unfamiliar with the lights and fearing that a catastrophe had
occurred somewhere in the north, flooded police switchboards
with calls.

    The two great flares of March were not isolated events. Nine
other major outbursts and hundreds of smaller ones were recorded
during the two weeks it took for the sunspot region to rotate
out of view. In the months since, as the sun moves erratically
toward its maximum, several flares have been observed every day.

    The sun has long been pre-eminent in human thoughts and
actions. Almost from the beginning, people worshiped the sun as
the beneficent provider of light and life, and as a god, called
Ra by the Egyptians, Helios by the Greeks and Sol by the
Romans. To the Aztecs, the sun god was Huitzilopochtli, whom
they nourished with human sacrifices. Egypt's great pyramids at
Giza were built with their sides aligned with the rising sun at
the vernal equinox, and the temple complex at Karnak was
dedicated to Ra. The ancient circle at Stonehenge, in England,
was apparently constructed so that the sun would rise over one
of the great stones at the time of the summ-er solstice.

    From the beginnings of history and literature, human beings
have also invoked the sun. In rejecting peace offers from Darius
before the battle of Gaugamela, Alexander the Great explained,
"Heaven cannot brook two suns, nor earth two masters." And in
1911, Kaiser Wilhelm II of Germany, speaking of his nation,
declared, "No one can dispute with us the place in the sun that
is our due."

    Through the centuries, few natural phenomena have inspired
as much fear and awe as solar eclipses. The ancient Chinese used
firecrackers and gongs to drive away the spirit they thought was
devouring the sun. Mark Twain's Connecticut Yankee, aware that
a most timely total eclipse was going to occur, escaped being
burned at the stake by King Arthur's knights when he predicted
that the sun would disappear. A benign form of sun worship
continues to this day, not only among beachgoers but also by a
group of intrepid American astronomy buffs who have traveled
around the world by plane, ship and jeep, from Java to Siberia
to Africa, to view each of the past dozen total eclipses.

    Even in ancient times, however, an occasional hardy soul
refused to deify the sun. The Greek philosopher Anaxagoras
brazenly claimed that it was merely a ball of fiery stone, and
was arrested and banished from Athens for his blasphemy. But
his radical concept caught on and was later refined by
Aristotle, who proclaimed the sun an unchanging sphere of pure
fire, devoid of any imperfections.


    Aristotle's view prevailed through the Middle Ages, was
embraced by Christianity and went largely unquestioned until
Galileo and other early 17th century sky watchers pointed the
newly invented telescope at the sun and saw black spots on its
surface. So much for solar purity. Despite clerical
disapproval, the reality of sunspots was quickly accepted.
Still, more than two centuries passed before Samuel Heinrich
Schwabe, a German apothecary and amateur astronomer, discovered
the strange, cyclic behavior of the solar blemishes.

    Schwabe had been searching for the hypothetical planet
Vulcan, supposedly the closest one to the sun, hoping to spot it
in silhouette as it moved across the solar disk. In the process,
he observed and kept meticulous records of sunspots over a
17-year period. Finally, in 1843, he recognized and announced
the eleven-year cyclic nature of the spots and wrote, "I may
compare myself to Saul, who went to seek his father's ass and
found a Kingdom."

    In the years since, by tabulating sunspot records going back
to the early 18th century and using improved telescopes,
satellites, advanced instruments and modern theory, scientists
have become ever more familiar with the bizarre dance of the
sunspots. Each cycle begins when spots show up in both the
northern and southern hemispheres about 35 degrees away from
the solar equator. As the cycle matures and the older sunspots
fade away (some last only a few hours, others for weeks and
even months), new and more numerous spots appear at lower
latitudes. Toward the end of the cycle, diminished in number,
they appear at latitudes some 5 degrees from the equator.

    Sunspots tend to travel in pairs or groups of opposite
polarity, like the ends of horseshoe magnets poking through the
solar surface. During one eleven-year cycle, as the blemishes
traverse the face of the sun in an east-west direction, the
leading spots of each group in the northern hemisphere will
generally have positive polarity, the trailing spots negative.
In the southern hemisphere, the leading spots will be negative.
During the next cycle, the hemisphere polarities will reverse.
On average, then, 22 years will pass between solar maximums of
the same sunspot polarity. This suggests to many astronomers
that the fundamental solar cycle is 22 years rather than eleven.

    Since the sun in myriad ways governs the very existence of
all terrestrial life, the cyclic changes in the sunspot
population have, ever since Schwabe, inspired speculation about
their effect on solar radiation and, consequently, on the
earth. Though the sun is a rather ordinary star, its vital
statistics are breathtaking by earthly standards. Some 865,000
miles in diameter, it consists largely of hydrogen (72%) and
helium (27%) and is 333,000 times as massive as the earth. Solar
temperatures range from about 27 million degrees F* in the core,
where 600 million tons of hydrogen are fused into helium every
second, to 10,000 degrees F on the photosphere, or surface.



-- J. Madeleine Nash/Sunspot

*To astronomers, the eastern edge of the sun is to the left, as
viewed from earth.

*If current theory is correct. But only about a third the number
of neutrinos (particles with little or no mass that travel at
the speed of light) that the sun should be producing at this
temperature have been detected, leading some scientists to
speculate that the core temperature is lower.