THERE MAY BE nothing new under the sun, but 93 million miles away on and in the sun there is hot news aplenty.
Though the sun appears to earthlings as a benign, featureless source of warmth, light and a great tan, its looks are deceiving. True solar devotees describe the sun as a strange and mysterious orb, a seething cauldron of superheated gases contorted by intense magnetic fields, huge shock waves, explosive flares, violent eruptions and supersonic winds blowing all the way to Earth and beyond.
The ”sun worshippers” who describe our star, the sun, this way have not come by their information on the beaches of St. Tropez. Rather, they are astronomers and physicists who have pieced together the current understanding of this life-giving celestial body from years of observations and theoretical calculations.
”Solar physics is at the real heart and soul of astronomy,” declares Dr. Eugene N. Parker, a University of Chicago physicist who coined the phrase ”solar wind” in the mid-1950s and predicted its existence. ”Pulsars, black holes and other X-ray (high-energy) objects are fashionable topics today, but the sun is the only emitter of X-rays where you can see what is going on. When we can explain what is happening on the sun, we will be able to explain what is happening on other stars. But right now, if you look closely at the sun, everything is mysterious and contradicts almost everything we thought we knew.”
There are, of course, some basic accepted facts about the sun. Located near the outer edge of a spiral galaxy, the sun is ”very much a run-of-the mill star,” says Dr. Robert W. Noyes, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and author of ”The Sun, Our Star.”
It is ”average” in size (860,000 miles in diameter, or more than 100 times that of the Earth`s), age (5 billion years old) and brightness (100 times dimmer than some of the Big Dipper`s stars).
Like all stars, the sun generates its energy deep in a hot, dense, rotating core where the temperature is an incredible 15 million degrees Celsius.
”Every second,” Noyes says, ”the sun processes about 700 million tons of hydrogen, converting it into helium. About 5 million tons are transformed into pure energy, but only a tiny amount of this energy is actually radiated outward from the core.”
About 70 percent of the way to the surface, the process of ”convection” takes over from radiation, and energy is carried the rest of the way to the surface in circulating eddies of hot gases. From there, energy passes rapidly from the surface up through the sun`s lower atmosphere, the chromosphere, and its outer atmosphere, the corona. A fraction–1 part in 2 billion–of the energy leaving the surface of the sun is intercepted by Earth, traveling this final interplanetary distance in 8 1/3 minutes.
In addition to visible light, the sun`s energy is in the form of radiowaves and ultraviolet, infrared, gamma ray and X-ray radiation. Almost all of what scientists know about the sun comes from analyzing this radiation. Their findings fill volumes.
But there are plenty of unanswered questions. Consider, for example, the sun`s most impressive and influential feature: its magnetic field.
Discovered in 1908, the field originates inside the sun, the result of rotational and convective motions. Virtually everything that happens on the sun is related to its magnetic field, which also interacts with the Earth`s much weaker magnetic field.
And yet, Noyes says, ”scientists still do not have a clear understanding of how the sun`s magnetic field works.”
For starters there are sunspots, dark areas of magnetic activity on the solar surface, which have been observed to come and go since ancient times. The number of sunspots reaches a peak in a cycle that repeats itself approximately every 11 years.
Even more puzzling is the case of the corona, a hot, thin, gas where the sun`s magnetic field manifests itself in strange and spectacular structures and events.
There, arches of magnetic fields thread through the superheated atmosphere like loops in a hooked rug. At some locations in this loopy lattice, there are large areas where the magnetic field loops are broken, and the field opens out into space. From these magnetically open areas, known as coronal holes, electrically charged atomic particles–the solar wind–rush out at speeds of 200 to 600 miles per second, bathing the Earth and interplanetary space with the very stuff of stars.
”We now know that the corona`s temperature is somehow caused by the conversion of magnetic energy into heat energy,” CFA astronomer Dr. George L. Withbroe says, ”but we don`t exactly know how this is done. Nor do we understand, for example, why solar wind velocities are so great or how solar flares are generated.”
To help seek answers to some of these questions, the space shuttle will launch a small satellite in October, 1986, carrying a coronal spectrometer designed by CFA astrophysicist John Kohl in collaboration with Withbroe and other scientists. This device, an instrument which reveals the ultraviolet spectrum of the normally invisible corona by creating artificial solar eclipses, will help identify the physical processes involved in the generation and acceleration of the solar wind.
Future studies may soon shed light on these and other solar enigmas, including what lies at the very core of the sun. Scientists have discovered that the sun is vibrating, and they can detect this ”global oscillation”
using the new techniques of ”helioseismology,” which are similar to those used in terrestrial seismology.
The global oscillation is actually made up of millions of tiny oscillations, each with its own characteristic frequency and geometry and reflecting conditions deep inside the sun`s interior. To detect these minute motions, the National Solar Observatory in Tucson, Ariz., is currently setting up a worldwide Global Oscillations Network Group (GONG) to provide 24-hour-a day solar monitoring with optical telescopes.
”GONG will provide the first detailed information on the structure and dynamics of the sun`s interior,” NSO Director Robert Howard says, but even current studies are beginning to reveal patterns of rotation and convection in the interior. ”Helioseismology,” Noyes says, ”may provide the key to the way these motions generate the magnetic fields which produce sunspots, the hot corona, flares and the solar wind.”
Astronomers also are eagerly anticipating the large, orbiting Solar Optical Telescope, planned for launch in the 1990s. ”Some of the most important magnetic structures on the sun are just too small to see from Earth,” Parker of the University of Chicago says. ”The Solar Optical Telescope will be able to see the motions of the structures that we think are involved in the conversion of magnetic energy into heat energy and resolve those structures right down to the footpoints of the magnetic loops.”
Adds Parker: ”The Solar Optical Telescope will not only answer the $64 question: Why is the corona so hot? It will help solve many mysteries in the universe.” But not all, for contrary to popular belief there will always be something new under the sun.
