Oke was not solely an instrument-builder; he was also interested in the data gleaned from the observations made with his instruments. His doctoral thesis, submitted at Princeton in 1953, was in fact a theoretical study, of the atmospheres of O-type stars — the most massive, hottest stars that burn hydrogen as their main energy source. Later, he moved into observational spectroscopy and this dominated his scientific interests for the rest of his career.
When Oke joined the Caltech faculty in 1958, he built a single-channel scanner, which could measure 10-nm-wide segments of the spectrum of a star or galaxy successively, by stepping a diffraction grating through the appropriate angle. Using this photometer, Oke became a key player in one of the most momentous events in modern astronomical history — the discovery, in 1963, of the large redshift of the quasar 3C273. (Redshift is a measure of an object's distance from the Earth.) Although we now know quasars to be extremely luminous, distant stars marking the centres of galaxies, at that time they were an enigma. Using the Hale telescope, Oke's Caltech colleague Maarten Schmidt identified the pattern of emission lines in the spectrum of quasar 3C273 as the Balmer series of lines from hydrogen atoms. The lines were difficult to recognize because they had been shifted to such long wavelengths — a consequence of the quasar's large redshift. Schmidt identified the Balmer series up to the so-called Hβ line from his photographic spectra of 3C273. Oke used his own photoelectric scanner to detect another line, Hα; his paper followed Schmidt's in Nature.
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