Split Starlight

Astronomers heard big news: Astro-Physicist Otto Struve and his staff at the University of Chicago's Yerkes Observatory had perfected a powerful new spectrograph for photographing invisible infra-red radiations from the stars. Since the instrument can be used in broad daylight, stargazers can now go on a 24-hour shift.

Photographing infra-red (heat) rays is not new, but Professor Struve's spectrograph is much more sensitive than any previously made. Using new red-sensitive plates developed during the war, and a gold-coated mirror (which reflects infrared rays better than a silver-plated one), the instrument can catch rays of wavelengths twice as long as those visible to the naked eye. Its special advantage for daylight work is that, while visible light from the stars is scattered by the earth's atmosphere, the longer infra-red rays get through with relatively little interference.

Among the Molecules. Astronomers get almost all of their information about the composition of stars from the spectrograph, which splits starlight into spectral lines each identifying a particular element or compound. But visible light tells only part of the story; at least half of the sun's radiation, for example, is in the invisible infrared. If astronomers could identify the material giving off these invisible radiations, they would know much more about the make-up of the universe.

They suspect that most of the infra-red radiations come from molecular compounds, rather than separate atoms. A star's brightness varies with its temperature: the hotter the star, the bluer or whiter its light--just as a piece of heated iron first glows a dull red, becomes whiter as it gets hotter. At the temperature of a hot star (10,000DEG or more at the surface), all material is broken down into independent atoms. But there are outer layers of cooler molecules giving off only infra-red radiation. Professor Struve's spectrograph, which can photograph invisible wavelengths of more than 10,000 Angstroms (visual limit: 7,500 Angstroms), is designed to study these layers in stars and planets.

A Struve assistant, Dr. Gerhard Herzberg, who is one of the world's top authorities on molecular physics, last week had an exciting report to make: after a trial of the new spectrograph at MacDonald Observatory in Texas, he had discovered new bands of carbon dioxide in the spectrum of the planet Venus and methane in the spectrum of Jupiter. He plans, next winter, to study the faint planet Uranus, whose atmosphere is still a complete mystery to astronomers. Mars is also slated for early examination; the spectrograph, by analyzing the planet's atmosphere, may give astronomers some new leads to the old question of whether or not life on Mars is possible.

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