Science: Sunspots & Radio

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The hot belly of the sun last week erupted in an acne of sunspots, a chain of splotches 160,000 miles long. This was the strongest sunspot activity since the sun entered a new cycle two years ago (TIME, Nov. 13, 1933), started climbing irregularly toward the intensity peaks due in 1938. Vortices of cooling gas on the solar surface, sunspots in their times of vigor have been associated by scientists with magnetic disturbances on Earth and poor radio reception.

A new view of sunspot effect on radio was presented last week in Science by Radio Section Chief John Howard Dellinger of the U. S. Bureau of Standards. Dr. Dellinger had noticed a curious fade-out of daytime reception of high-frequency signals, occurring at almost uniform intervals approximating 54 days, twice the sun's rotation period. These mysterious mufflings, lasting a few minutes, were perceived this year on March 20, May 12, July 6, Aug. 30. Accordingly Dr. Dellinger predicted another fade-out on or just before Oct. 24.

Fortnight before that date a burst of sunspot activity began. Nevertheless high-frequency reception over that half of the world lighted by the sun improved instead of faltering. Indeed by Oct. 21-23 it was the best the Bureau had ever observed. Next day—the crucial day—reception fell off sharply by half, and the expected fading occurred. Simultaneously the uppermost main layer of the ionosphere (radio-reflecting region of electrified air) rose from 155 mi. to a record height of 285 mi.

Dr. Dellinger now believes that high-frequency daytime reception improves with sunspot activity, possibly because increased ultraviolet radiation from the sun at such times makes more ions in the ionosphere. The magnetic shifts resulting from the ultraviolet bombardment, however, may cause delayed interferences with low-frequency reception and night reception in general.

The 54-day fade-outs seem to be due to sudden, localized disturbances on the solar surface. To confirm this Dr. Dellinger asked Mt. Wilson Observatory if anything peculiar had showed up in the spectrohelioscope observations on the fade-out days. Back came word that on July 6, Aug. 30 and Oct. 24, within a few minutes of the fading, huge clumps of gas on the sun had manifested marked changes in form and behavior.