National Geographic : 1956 Feb
One of These Sunspots Is Big Enough to Engulf the Earth Actually hot and bright, sun spots appear dark only in con trast to their blinding sur roundings. They show the solar atmosphere writhing in violent turmoil. Astronomers watch them closely because they sometimes cause auroral outbursts and radio disturb ances in the earth's atmos phere. Solar rotation carries the spots around the sun in about 27 days. They reach their peak in 11-year cycles. Ac tivity was severe on July 26, 1946, date of this photograph. IGY observers will watch sunspots closely in 1957-58, hoping to discover their cause. Outbreaks pictured here ex tend a distance of some 155, 000 miles, about one-fifth the sun's diameter. Enlargement shows the dark cores, which astronomers call umbrae. Mt. Wilson Observatory 296 programs be interspersed with periods of maximum effort. Intensified observations are much to be desired during days when atmos pheric conditions are especially favorable, and at other times when unusual manifestations occur on the sun. Each month will include three or four days, called Regular World Days, picked for their coincidence with special phases of the moon. Quarterly 10-day periods, entitled World Meteorological Intervals, also have been marked off. Weathermen all over the world will spur themselves to redoubled efforts at these times. In addition, warnings from communication centers in the United States, Alaska, Japan, Australia, and the U.S.S.R. will alert all sta tions to Special World Intervals. These periods, of perhaps a few days' duration, will be singled out when forecasters expect unu- sual solar, magnetic, au roral, or ionospheric activity. Special World Intervals also will be an nounced at times of solar eclipses and unusual me teor showers. During each of the spe cial periods the frequency of observations of all phe nomena will be drastically stepped up, on the principle that the more scientific lines are out, the more likely will be notable catches of unusual and useful data. Analysis centers will call on electronic com puters to digest the mass of information re sulting from readings that, during intense magnetic storms, may follow one another as closely as every 15 to 30 seconds. Stirring action will be the lot of explorers, engineers, and arctic experts who push to completion IGY researches in high latitudes. From Canadian, Danish, and United States bases and weather outposts in the Far North, trained task groups will head out by ship, dog sled, tractor train, and aircraft to fill in some of the big blanks in our knowledge of the Greenland Icecap and of polar Canada.* The * See "Wringing Secrets from Greenland's Icecap," by Paul-Emile Victor, NATIONAL GEOGRAPHIC MAGA ZINE, January, 1956.