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Now, the optical astronomers turned to one of their most powerful tools: the spectrograph, which separates light into its component wave lengths by passing it through a prism or a series of fine lines etched on a glass plate. The spectrum of colors that results can be photographed and interpreted by scientists to reveal the secrets of the light's source.
Superimposed on a rainbow of colors ranging from short-wave-length violet light at one end to longer-wave-length red at the other, star spectra show a series of characteristic bright and dark vertical lines that indicate the presence of specific chemical elements. In 1868, one such line in a spectrogram of the sun enabled British Astronomer Norman Lockyer to detect the existence of a new element—helium—before it was discovered on the earth.
Using the 200-in. giant at Palomar, Astronomers Allan Sandage and Jesse Greenstein channeled the faint light from a quasar through spectrographs, using exposures as long as six or seven hours to produce a usuable image on their film. Their painstaking labor produced tiny spectrograms that contained no color, only shadings of black and white, and were one-third of an inch long and a thousandth of an inch thick. Under the microscope, however, Sandage and Greenstein were barely able to discern strange patterns and spectral lines that had never before been observed in stellar spectra. Genuinely puzzled, Greenstein began to work out an elaborate hypothesis suggesting that the quasars were extremely dense and hot nearby objects, probably the remnants of supernovas containing highly excited or unfamiliar elements.
Strange Lines. In 1962, a group of radio astronomers led by Cyril Hazard tried a subtle tactic in an effort to pinpoint a strong radio source that searchers with optical telescopes could not identify. Pointing the Parkes, Australia, 210-ft. dish antenna toward the source, known only as 3C 273,* Hazard's group recorded the precise time that its signals were eclipsed, or blotted out, by the sharp leading edge of the passing moon and the time when they reappeared from behind its trailing rim. Because the position of the moon can be accurately calculated for any given time, the Australians' "lunar occultation gave them an accurate position of the elusive radio source.
When the Australian data reached Astronomer Maarten Schmidt late in 1962, he was able to locate 3C 273 in earlier photographs, which revealed it to be a round, fuzzy, starlike object with a faint, glowing jet protruding from it; he had discovered a quasar that was brighter than any yet recorded by his colleagues.
Soon after, he obtained a good spectrum from the quasar and, like his colleagues Sandage and Greenstein, he was puzzled by the sight of unfamilar spectral lines. But after staring at the spectrum for six weeks, Schmidt had a wild, almost desperate thought. Three closely spaced spectral lines on his photographic plate resembled hydrogen lines. But they were not in the blue segment of the spectrum where they belonged: they were superimposed on the red portion instead. Could they actually be hydrogen lines that had shifted to longer wave lengths?