What's new under the sun
editOn April 4, 1980, a new American spacecraft named Solar Max made one of the most unsettling discoveries in the history of science. It detected a sudden drop in energy coming from the sun. The sun's radiance dimmed by only two-tenths of one per cent, and returned to normal in four days. However, a month later, it dipped again for five days. The evidence was unmistakable - the sun, on whose light the life of our planet depends, was flickering like a candle in an unseen breeze. The earth is a solar-powered planet, where 98 per cent of its warmth comes from sunshine (the rest from geothermal heat). Solar energy lifts rain clouds, drives winds, and is responsible for photosynthesis in plants that feed all living things. If its brightness dimmed by only two per cent for a decade or more, climate scientists estimate that most places where snow falls in winter, may be forced to endure frost or snow through out the year
Since ancient times, when the sun was worshipped as divine, people have assumed it is perfect and unchanging. In seventeenth century Italy, Galileo was persecuted when he dared to suggest that the sun was imperfect - his primitive telescope had picked up dark blemishes, or "sunspots".
Modern scientists have portrayed the sun as a constant bright star. They see it not as a god, but a ball of gases 864,000 miles across that was born four million years ago when a huge cloud of hydrogen atoms was condensed. The immense pressure of gravitational collapse ignited a nuclear fusion reaction in the cloud's heart. In that 27-million-degree Fahrenheit furnace, 600 million tons of hydrogen are converted into energy, producing X rays, gamma rays and other radiation that takes more than a million years to squeeze through it's dense inner mass and reach the surface, resulting in sunshine.
The sun's surface is a violent place, where vast explosions - solar flares - often erupt, some as powerful as ten million one megaton H-bombs. Sunspots also spread across the sun's face in 11-year cycles, and the peak of sunspot cycles tends to coincide with a peak in solar flares.
Despite this turbulence, scientists, until a decade ago, assumed that the sun's radiance was unwavering. However, by the early 1980s, new evidence was raising some doubts about the sun's consistent nature. Some Nasa ground-station measurements seemed to suggest that the sun shone with up to two per cent more energy at the peak of sunspot cycles. American atmosphere researchers also detected similar variations.
Was our sun constant? Or did its light occasionally brighten or fade? As recent record-cold winters chilled the world's snow belt and droughts laid waste to subtropical lands, these questions took on special urgency and sparked a worldwide scientific undertaking from which a completely different picture of the sun is emerging.
As the most recent sunspot cycle neared its peak, scientist at 60 observatories in 18 countries coordinated their work to learn more about it. This global effort was named the International Solar Maximum Year (ISMY), which continued for 19 months, from August 1979 till February 1981.
As part of its 10 years, a $5 billion commitment to investigate the sun was launched by Nasa -the Solar Max in February 1980. This $80 million, 5,000 pound spacecraft settled into orbit 357 miles above the earth and turned its sensor eyes towards the sun, 93 million miles away.
On April 4 1980, Solar Max detected a drop in energy coming from the sun. The "solar constant" that scientists had believed for so long was not constant. Clearly, it is a variable star.
This finding did not surprise astrophysicist Jack Eddy of the National Center for Atmospheric Research in Boulder, Colorado. Four years earlier, he had found historical evidence that the sun flickered and varied. Eddy had been examining records of sunspot activity that astronomers had made ever since Galileo's discovery. In the 1890s, E. Walter Maunder of Royal Greenwich Observatory in London had noticed an odd pattern in the same records. Sunspots seemed to vanish almost completely between AD 1945 and 1715.
Few astronomers took Maunder's claims seriously. Now, some 80 years later, Eddy looked into his "maunder minimum," and produced corroborative evidence that the sun really did shed most of its spots for 70 years. Eddy found that astronomers in China had reported the same seven-decade disparity. Scandinavian records showed the northern lights had also dimmed greatly between 1645 and 1715.
Carbon-14 in tree rings produced further evidence. When sunspots are numerous, the solar wind intensifies and drives cosmic rays away from the solar system. The isotope carbon-14, created when carbon atoms collide with cosmic rays, thus becomes less common, and this becomes apparent in plants. Since trees add a growth ring to their circumference each year - and some trees are 5,000 years old - they can tell us how much carbon-14 was in the air long ago.
Tree ring analysis seemed to prove Maunder right. Carbon-14 levels were exceptionally high between 1645 and 1715, suggesting a drop in sunspots then. However, the evidence shocked Eddy, for it did not stop with Maunder's minimum. Carbon-14 revealed a major decrease in sunspots between 1400 and 1510. Eddy also discovered a sunspot maximum, which he named the medieval maximum.
In all, Eddy found 12 major variations in sunspot activity during the past 5,000 years - including a maximum that began at about the time of Jesus' birth. Each was accompanied by changes in global weather and climate.
During the Maunder Minimum, Europe was devastated by severe winters, also referred to as the Little Ice Age. River Thames repeatedly froze in London, as did Rio Grande in North America. The Medieval Maximum, by contrast, marked a time of record balmy warmth in Europe, when there was a population explosion in Scandinavia and the Vikings colonized apparently temperate places they named Greenland and Vinland - today's cold lands of Greenland and likely Nova Scotia, when one was green and the other had wild grapevines. Those warm centuries ended quickly with a reversal on the sun. Bitter chill swept Europe, and colonists everywhere in the North Atlantic died.
Next, Eddy considered our own time. Carbon-14 in tree trunks reveals that we have been living during a modern maximum of unusually high sunspot activity. What we think of as normal weather is, instead, abnormally warm. In this fair-weather century, abundant food production has helped to swell our planet's population from 1 billion to more than 6 billion. What will happen when the sun reverts back to its normally inactive behavior? Historically, periods of warmth such as ours have been brief, and have ended abruptly.
Eddy's studies raise another disquieting observation - the sun appears to be shrinking faster than scientists thought possible. Studies, in fact, suggest that the sun will burn itself out in five billion years. Eddy speculates that the current shrinkage is evidence of a slow but powerful oscillation - a time when the sun's enormous gravity is flexing its muscle and causing temporary contraction in its diameter, and with it a possible change in the brightness of the sun. A fluctuating rate of shrinkage, he believes, is another instability of our variable star.
If Eddy's speculation is right, then a significant share of the sun's energy may be produced not by atomic fusion alone, but by oscillation in its outer skin. In the sun's fusion furnace, electrons are blasted free of atomic nuclei, creating giant electrical currents that boil upward. Whenever electricity flows, it generates electromagnetic fields. Scientists surmise that those fields form magnetic tubes, which circle the rising flow of electrons. When the tubes break through the sun's surface, they produce sunspots.
In 1980, "rivers" of solar magnetism were discovered on the sun's surface. Astronomers Robert Howard and Barray J. LaBonte at Hale Observatories in California detected currents that once every 11 years initiate slow spiral-like stripes on a rotating barber's pole-across the sun from its North and South poles. Rivers of current flow simultaneously from the two poles. After a 22-year migration, as rivers near the sun's equator, they vanish as mysteriously as they appear.
These rivers appear to be a key to sunspots, for when they reach about 30 degrees north and south of the solar equator, sunspots begin welling up between them.
Sunspots come in pairs. They look dark and are cooler than the surrounding face of the sun because their powerful magnetic fields hold down gases that elsewhere boil upward. They fade away when magnetic rivers dissipate, apparently submerged into the sun.
In April 1980, as Solar Max watched, a magnetic loop surged upward from the sun's surface and drove away a huge magnetic arch that swayed above it. The action was caused by a solar flare, one of the most violent events known in nature.
Blowing like a hurricane through electrified solar wind that envelops half our solar system, a solar flare can have devastating impact on our planet. The first shock wave to hit is a flash of X rays, striking the atmosphere about eight minutes after leaving the sun, and causing radio blackouts, disrupted satellite signals and ghosts on radar screens.
An hour after the flare, a wave of high speed solar protons (the stripped nuclei of hydrogen atoms) reaches the earth. Then come days of bombardment by a fast-moving flotsam of particles and magnetic fields. They light the Aurora Borealis, send electrical charges through telephone lines and cause power blackouts. Solar flares also erode the ozone layer in the earth's atmosphere, opening it to more ultraviolet light, which can cause skin cancer.
For decades, scientists have been looking for links between sunspot activity and weather. Proof is difficult because the earth's machine is complex. But we now know that when a solar flare erupts, it heats our world's upper atmosphere, causing it to expand. In 1979, as sunspots climbed to a near-record number, such unexpected expansion dragged Skylab, the first sophisticated space station, to a fiery burn-up, years before it was to have come down.
Every 22 years for the past several centuries, drought has struck the high plains in United States, most recently during the past few years and right before the Great Depression. Is there a connection with the 22-year sunspot cycle? Scientists suspect so, but they have not been able to pinpoint as yet. Several researchers have found that as solar activity increases, so does the incidence and intensity of lightening storms. But will such activity in the earth's atmosphere increase or decrease the amount of rainfall, the force of winds, the degree of cloudiness? Like the sun itself, the answers vary.
The sun's influence on out planet's magnetic field apparently alters the course of giant rivers of wind high in the earth's atmosphere, such as the jet stream. Between 1996 and 1999, the jet stream brought record winter chill to eastern United States. Solar scientist at the time observed that the number of sunspots on sun's face was increasing more slowly than expected. But by early 1999 sunspots were coming to life, and in March 2000, the second strongest sunspot peak ever was recorded. The winter had been balmy. The summer of 2000 would bring an extremely devastating heat wave and that is what happened.
Thanks to Solar Max and other researches, we are beginning to understand the ways the sun touches our lives. Of course, we have yet to discover why this star flickers. But one thing is certain - the star we were born under will determine our fate and our future.