Science/Medicine : Studying the Sun : Eclipses may be spectacular, but brightest hope in solar research lies in X-rays
In March, the sky will put on one of its most dazzling shows.
It will begin when the moon inches between the Earth and the sun in the middle of the morning on March 18, at first blocking out the edge of the only star in the universe essential to life on Earth. Less than an hour later, just moments before a total eclipse, sunlight will flash through the deeper valleys of the moon, producing brilliant jewels of light.
After a few seconds, the moon will move directly between the sun and the Earth, dramatically changing the landscape below.
At totality, only the sun’s outermost layer--its corona--will be visible, transforming the sun into a celestial diamond ring, a darkened globe embraced by a gossamer circle of light.
Along a narrow band across Indonesia and the Philippines, the day will become night. Some flowers will close, wildlife will exhibit nocturnal behavior, and the Earth, bathed in only the light that comes from the sun’s atmosphere, will cloak itself in strange hues. Stars will shine in the darkened day.
For centuries, total solar eclipses, which occur several times each decade, offered scientists their best chance to study the sun, but today modern instruments in space can do the job better by, in effect, creating their own eclipse. And astronomers have tools and techniques, including the use of radiation from the sun in varying wavelengths, to produce images that would not have been possible just a few years ago.
Historically, eclipses were important because when the intense light of the main body of the sun is obscured by the moon, the sun’s atmosphere can be observed, and it’s no peaceful place.
Giant solar “prominences,” with mountains of light 100,000 miles high, rise and fall from the surface. Solar flares, intense patches of high energy, throw out matter at speeds of more than 2 million m.p.h. Solar winds with highly charged subatomic particles stream from the sun and streak to the outer limits of the solar system, blowing dust particles from the surface of comets hundreds of millions of miles away, forming glowing tails on ice balls that would otherwise pass through the heavens unnoticed.
But the sun is no exceptional star. Astronomers call it an “ordinary” star, not unlike trillions of others that dot the sky. It is a middle-aged, average performer, yet the source of all life on Earth, and an enormous mystery to scientists who have devoted their careers to probing its secrets.
“It’s so complex,” says Roger K. Ulrich of UCLA. “My colleagues think I’m nuts” for working on a subject that is “so hard nobody wants to mess with it.”
Ulrich’s partner these days, Ed Rhodes of the University of Southern California, agrees about the sun’s complexity, but he adds another reason why so many scientists have shied away from studying the sun.
“It’s so close,” he said.
The lure of distant objects that were unknown just a few decades ago is irresistible to most astronomers, and most of the action these days is concentrated on “deep sky” exotica, like quasars and pulsars and black holes.
That leaves scientists like Rhodes and Ulrich with a paradox. The space age has provided extraordinary opportunities for studying the sun through instruments that can be placed above the distorting effects of the Earth’s atmosphere--where they can also use forms of radiation that do not even reach the ground--but a wide range of space programs have been shelved in this age of lowered expectations.
“We’re almost dead in the water,” said Stanford University physicist Arthur Walker after ticking off a series of projects that have stalled.
Indeed, support for solar research has been so curtailed that both Rhodes and Ulrich came up with their own funding to save programs that for awhile appeared to be doomed.
The two men spend much of their time these days at the Mt. Wilson Observatory above Pasadena where legendary astronomer George Ellery Hale discovered magnetic fields on the surface of the sun in 1908. Because of the work that began with Hale and continued through all those years, Mt. Wilson has been the source of much that is known today about the sun. Yet the Carnegie Institute revealed plans a few years ago to close Mt. Wilson and concentrate its limited resources on its observatory in Chile.
At stake, Ulrich said, was nothing less than the continuity of research that had been going on at Mt. Wilson for three quarters of a century. The observatory had been at the forefront in research on sunspots on the surface of the sun, pockets of lower energy that show up as slightly darkened spots drifting slowly across the surface.
It takes 11 years for the sunspots to complete one cycle, and it requires observations over many cycles--and thus many years--to confirm scientific findings. If the observatory closed, that continuity would be lost.
“I put my body on the line,” Ulrich said. “The thing at risk is this tremendous storehouse of information and the continuity.”
Ulrich came up with about $280,000 in annual funding from the National Science Foundation, the Office of Naval Research and the National Aeronautics and Space Administration to keep the program going. Each day, researchers working with Ulrich painstakingly chart the position of each sunspot and send that information to the National Oceanic and Atmospheric Administration in Boulder, Colo., where it is available to any scientist studying the sun.
The importance of that continuity was demonstrated earlier this year when a German scientist, Karin Labitzke, found what other scientists have described as “the best correlation yet” between sunspots and weather patterns on Earth. Labitzke presented her findings in early December at the American Geophysical Union convention in San Francisco.
Many other scientists have searched for some correlation between sunspots and weather patterns on Earth, but with no success.
Labitzke concentrated her research on the periods when the sunspots are plentiful, called the “solar maximum.” During that period, the sun is at its most active phase, and unusually powerful solar winds blow electrically charged particles across the solar system, some of which become trapped by the Earth’s magnetic field and stream toward the surface near the Earth’s poles in a process that causes the aurora borealis in the north and the aurora australis in the south, known as the northern and southern lights.
Labitzke concluded that other scientists may have failed to find a correlation between sunspots and weather patterns because the effect occurs under only certain conditions. Thus data from periods when the effect could not occur would cloud the issue.
She was especially intrigued by one meteorological mystery. Winds in the Earth’s equatorial region blow either easterly or westerly for two or three years, and then reverse the direction.
And when Labitzke plotted sunspots and temperatures in the higher latitudes near the North Pole for periods when the equatorial winds were blowing toward the west, there seemed to be a strong correlation. She found that high altitude temperatures near the North Pole were considerably warmer during periods of high sunspot activity and westerly equatorial winds--but not when the equatorial winds were blowing to the east.
The fundamental problem with her research at this point is the fact that no one knows why that correlation should exist, or what kind of meteorological mechanism might be at work. What remains to be done is to continue that research, using data supplied by scientists like Ulrich, to see if the apparent correlation holds up over many solar cycles.
While Ulrich plots sunspots with the 150-foot solar tower at Mt. Wilson, Rhodes is using the observatory’s 60-foot solar tower to push the frontier of modern solar research. Rhodes is something of a pioneer in the new field of “helioseismology.”
Like geologists who learn about the Earth’s interior through the study of earthquakes, astronomers are now learning much about the interior of the sun by studying pulsing “oscillations” on the surface of the sun. These oscillations appear to rise and fall in five-minute patterns, apparently driven by huge convection cells rising from deep within the sun.
One outgrowth of that research, Rhodes said, is the confirmation of a theory that the outer layers of the sun rotate much more slowly than the sun’s core. His research suggests that the core may, in fact, be spinning two or three times as fast as the sun’s surface.
Rhodes is part of a NASA task force studying the possibility of putting instruments in space to analyze the oscillations, regarded by many astronomers as the single most promising area in solar research. Sources said that program will probably be funded by the space agency.
Space-borne instruments have two main advantages. They can be positioned in areas where they can look at the sun continuously rather than only during daylight hours on clear days, thus greatly expanding continuity, and they can “see” things that cannot be seen from Earth.
Varied Wavelengths Employed
“It turns out that many of the most interesting phenomena on the sun are most readily observed in X-rays, gamma and ultraviolet wavelengths--none of which penetrate the earth’s atmosphere,” said Stephen Maran, a senior staff scientist with the Goddard Space Flight Center in Greenbelt, Md.
An X-ray camera in space thus can produce images of the sun that are quite different than images that can be seen in the visible light range, and some wavelengths are particularly well suited to studying different events.
Nowhere is that more true than in the study of the sun’s atmosphere, according to Stanford’s Walker.
“The understanding of the atmosphere was enormously advanced by space research,” said Walker, who was a member of the commission that investigated the explosion of the space shuttle Challenger. “The atmosphere is hotter than the surface, and that’s hard to understand.”
The surface of the sun is about 6,000 degrees, but the atmosphere ranges as high as 100 million degrees, Walker said. The source of that high atmospheric temperature is thought to be either electric or magnetic, but the process is not well understood.
One nifty result of the difference is that the atmosphere emits radiation at much shorter wavelengths than the surface of the sun, so instruments in space, such as X-ray cameras, can use those shorter wavelengths to “see” the atmosphere without interference from the sun itself.
That, historically, is what astronomers have used eclipses for. When the sun was blocked out by the moon, they were able to study its atmosphere.
Walker recently sent a rocket aloft from the White Sands missile range in New Mexico. For five minutes, an X-ray camera on top of the rocket made images of the sun’s atmosphere, in effect creating its own eclipse by capturing only the shorter wavelengths emitted by the atmosphere.
That sort of research has lessened the scientific significance of a total eclipse of the sun, but that doesn’t mean scientists are inclined to ignore it.
It will be a longer eclipse than most, ranging up to three minutes and 46 seconds, depending on an observer’s position. But since the band of an eclipse is so narrow, only those directly in its path will see it. Across most of the world, in places like Los Angeles, this extraordinary phenomenon will pass unnoticed.
Such a great spectacle, which undoubtedly troubled ancient peoples, is one of nature’s precious gifts, a window onto vistas that otherwise would have been closed. And the fact that such an event occurs at all is nothing short of miraculous.
Comparative Sizes Noted
The sun is 400 times larger than the moon, yet both appear from Earth to be about the same size because the sun is 400 times farther away, thus making it possible for the lesser to obscure the greater. And it would never happen at all if the moon’s orbit did not carry it directly across the apparent path of the sun.
Now as ritualistic as it is scientific, astronomers will flock to the southwestern Pacific and the Indian Ocean in March to watch the sun and the moon perform their strange dance across the heavens.
Aboard such ships as the Queen Elizabeth 2 in the Java Sea and the Golden Odyssey in the Celebes Sea, scientists, authors, adventurers and the simply curious will gather in awe to watch what UCLA astronomer George O. Abell describes as “one of the most spectacular of natural phenomena.”
Aboard the Queen Elizabeth, for instance, will be Kenneth Brecher, professor of astronomy and physics at Boston University, who will lecture alongside the likes of science fiction writer Arthur C. Clarke and noted paleontologist Stephen Jay Gould.
But this will not be just a pleasure cruise, according to Brecher’s longtime friend, kibitzer and fellow astronomer, Goddard’s Maran.
Brecher, Maran said, will perform at least one experiment.
He will “lustily” strike a copper-bottomed sauce pan to see if it will restore the sun to full view as effectively as “the ancient Tibetan gongs that are customarily employed for this purpose,” Maran said.
And the show goes on.
Learning through solar eclipses
For centuries, total solar eclipses, which occur several times each decade, offered scientists their best chance to explore the sun. During an eclipse, the sun’s intense light is obscured by the moon and the sun’s atmosphere can be observed. The next major eclipse occurs March 18 across Indonesia.
Continual monitoring from ground observatories
For 75 years, the Mt. Wilson Observatory in Pasadena has been the source of much that is known today about the sun. Data taken from the observatory, which has been at the forefront of sunspot research, was recently used to prove a correlation between sunspots and weather patterns on Earth.
Space-borne cameras use X-ray technology
The space age has provided extraordinary opportunities for studying the sun through instruments that can be placed above the distorting effects of the Earth’s atmosphere. Much interest lately centers on the use of X-ray photography. X-ray cameras use shorter wavelengths to “see” the atmosphere without interference from the sun itself--producing images that are quite different than that can be seen in the visible light range. In October, scientists sent a rocket aloft from the White Sands missile range in New Mexico. For five minutes, an X-ray camera on top of the rocket made images of the sun’s atmosphere, like the one, below.
