Astronomy: The Prodigal Sun

For several days in November 1960, the earth was under attack. Enormous sheets of red and green light nickered in the night sky. Magnetic storms blacked out long-distance radio communications. Compass needles danced crazily and Teletypes printed page after page of utter nonsense. These phenomena were not caused by an alien invader but by the familiar and normally benign sun. In an outburst equal to the energy of a billion hydrogen bombs, it was bombarding the earth with exceptionally intense electromagnetic radiation and a dense hail of high-velocity particles.

The barrage of rays and particles was largely deflected by the Van Allen belts or absorbed by earth's protective blanket of atmosphere, and life on the planet was not endangered. But the magnitude of that solar storm still haunts space scientists. What if an equally severe onslaught were to occur this week, catching the Apollo 10 astronauts within their thin-walled lunar module—or in July, when the Apollo 11 astronauts are on the surface of the moon? If that happened, high-velocity particles would riddle the men, causing serious illness or possibly even death. The odds against such an occurrence are not prohibitive; just as in 1960, the sun is again near the peak of its eleven year cycle of activity, when violent outbursts frequently occur.

State of Turbulence. Astronomers are slowly solving some of the mysteries of the sun, but they have only a vague understanding of the processes that cause its dangerous outbursts. Although the sun is an ordinary, average-sized star, its dimensions and characteristics are staggering by earthly standards. It has a diameter of 864,000 miles (v. earth's 8,000 miles) and consists of 2.2 octillion tons of gaseous matter, most of it hydrogen and helium. In the 27 million-degree F. temperatures in the solar core, 564 million tons of hydrogen are converted by nuclear fusion into 560 million tons of helium every second. Thus, in a single second, 4,000,000 tons of solar matter are converted into energy —more energy than man has used since the beginning of civilization—and hurled into space in the form of heat, light and other radiation.

The surface of the sun, or photosphere, has an average temperature of 10,000 degrees F. Its most prominent features are sunspots—dark areas as large as 80,000 miles across. These spots usually occur in pairs and move from left to right, one spot leading the other, across the visible solar face as the sun rotates. They are probably caused by powerful magnetic fields generated by the flow of tremendous electrical currents (as high as 10 million million amperes) within the sun. Like the tips of a horseshoe magnet, the paired spots have opposite polarity—one positive, the other negative—and are joined together by powerful magnetic lines of force that loop above the solar surface. The lines confine the gases in the spots, so that they cannot circulate and bring heat up from the solar interior. As a result, gases within the spots are cooler—and thus appear darker—than gases in the surrounding areas.