Monday, September 21, 2009

September 21: Arthur Covington

Arthur Edwin Covington
September 21, 1913 – March 17, 2001

Arthur Covington is a Canadian physicist who made the first radio astronomy measurements in Canada. Through these he made the valuable discovery that sunspots generate large amounts of microwaves at the 10.7 cm wavelength, offering a simple all-weather method to measure and predict sunspot activity, and their associated effects on communications. The sunspot detection program has run continuously to this day.

Covington was born in Regina and grew up in Vancouver. He showed an early interest in astronomy, and had built a 5-inch (130 mm) refractor telescope after meeting members of the local chapter of the Royal Astronomical Society of Canada. He was also interested in amateur radio and operated station VE3CC for a time. He started his career as a radio operator on ships operated by the Canadian National Railways. He put himself though school and eventually earned a bachelor's degree from the University of British Columbia in 1938, and obtained his master's degree from the same institution in 1940 after building an electron microscope. He then moved to University of California in Berkeley where he received his doctoral degree in nuclear physics in 1942. He was still at Berkeley when he was invited to join the National Research Council (NRC) in Ottawa in 1942 as a radar technician, working at the NRC's Radio Field Station.

Immediately after the war Covington became interested in radio astronomy, and built a small telescope out of the electronic parts from a surplus SCR-268 radar combined with parts from another receiver originally built to test silicon crystal radio parts for radar applications. These electronics were attached to the 4 ft (1.2 m) parabolic dish from a Type III gun-laying radar. The system operated at a frequency of 2800 MHz, or a wavelength of 10.7 cm. Initially the instrument was pointed in the direction of various celestial objects, including Jupiter, the Milky Way, aurora borealis, and the Sun, but it proved too insensitive to pick up any source other than the Sun. So a solar study program was started. As time passed, Covington and his colleagues realized that the Sun's emission at 10.7 cm wavelength was varying, which was unexpected. Thinking at that time was that the solar emission at centimeter wavelengths would be simply black body emission from a ball of hot gas.

Covington became convinced that the effect was due to sunspots, as the flux appeared to vary with the number of visible spots. The resolution of the device, about seven degrees, made it impossible to "pick out" a spot on the sun's surface for study, making a demonstration of the claim difficult. An opportunity to directly measure this possibility presented itself on November 23, 1946 when a partial solar eclipse passed over the Ottawa area, and Covington was able to conclusively demonstrate that the microwave emissions dropped off precipitously when the Moon covered a particularly large sunspot. This also demonstrated that magnetic fields were instrumental in sunspot activity.

Covington remained the director of the ARO until he retired in 1978. One of the buildings at the Dominion Astrophysical Observatory was named in his honour in 2003.

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