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Hale, George Ellery

telescope fields sunspots discovered

(1868–1938) US astronomer: discovered that sunspots are associated with strong magnetic fields.

Son of a wealthy engineer, Hale had an early interest in astronomy and studied physics at Massachusetts Institute of Technology. Whilst still an undergraduate he invented the spectroheliograph, an instrument capable of photographing the Sun at precise wavelengths and now a basic tool of solar astronomy. In 1908 he discovered that some lines in the spectra of sunspots are split, and correctly interpreted this as being due to the presence of strong magnetic fields (the Zeeman effect). Together with he discovered in 1919 that the polarity of the magnetic fields of sunspots reverses on a 23-year cycle.

Hale realized that larger telescopes were essential in order for astronomy to advance and put much of his energy and organizational ability into providing them. In 1892 he persuaded Charles Yerkes, a Chicago businessman, to fund a 40 in (1 m) refracting telescope for the University of Chicago, still the largest refractor ever built. Hale followed this by arranging for the Carnegie Institute to fund a 60 in (1.52 m) reflector for the Mount Wilson Observatory, and for a 100 in (2.54 m) reflector financed by John D Hooker that was to remain the largest in the world for 30 years. His greatest achievement, however, was to persuade the Rockefeller Foundation to provide the money for a telescope that would be the ultimate in size for Earth-based observations–the 200 in (5.08 m) Mount Palomar reflector. Construction began in 1930 and was to take 20 years. It was for a time the most famous telescope in the world, although by 1975 it was second in size to the 236 in (6 m) telescope at the Soviet Special Astrophysical Observatory in the Caucasus. Later giant telescopes have mirrors built of close-fitting segments or are formed by optical linking of an array of separate mirrors.

Hales, Stephen [next] [back] Haldane, John (Burdon Sanderson)

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