Twenty years of physics: Astrophysics

MAY 01, 1968

Lodewyk Woltjer

RADIO SOURCES had just been discovered twenty years ago, but their nature was unknown. The 21‐cm hyperfinestructure line of hydrogen had been predicted but was not yet observed. Theories of stellar and galactic evolution were primitive: The origin of the elements was a mystery, and the nature of cosmic rays was obscure.

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Lodewyk Woltjer, Columbia University.

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