Image-Slicer

Splitting the light from a star or other celestial object into the bands and lines of a spectrum gives astronomers clues about how hot the body is, whether it is advancing or retreating, whether it is spinning, whether it is dense or thin, what it is made of. Unfortunately, for technical reasons, not all the light of a celestial image can be crammed into the spectrograph.

To get a clear spectrum it is necessary to work with a very narrow band of light; but, because of atmospheric distortion, the image comes in as a diffuse, approximately circular blob. In practice the light is therefore fed through a narrow slit, perhaps one-thousandth of an inch wide. This screens off most of the diffuse image, but wastes 90 to 95% of the light, squanders countless hours of exposure time on big telescopes, prevents spectroscopic analysis of the farthest visible nebulae or "island universes."

Dr. Edwin Powell Hubble of Mt. Wilson Observatory has detected nebulae 500,000,000 light-years away, but only up to half that distance have satisfactory spectra been obtained.

The problem of using light for spectra more efficiently has goaded skygazers for years. Astronomers at Mt. Wilson and California Institute of Technology were putting their money last week on a device called an "image-slicer," invented by Caltech's quiet, brilliant Ira Sprague Bowen. No bigger than a child's fist, this gadget splits up the blobby image of a star or nebula into a number of thin strips by means of a combination of mirrors which feed each one of the strips through the one-thousandth-inch spectroscope slit. After passing through, these slices of light are recombined into a single band, suitable for analysis, by a cylindrical lens. The Bowen image-slicer makes it possible to use 50% to 75% of the available light, instead of 5% to 10%. Physicist Rudolph Meyer Langer of Caltech declared that "the new method ranks with . . . the very greatest improvements in astronomical technique in several generations." In connection with Caltech's 200-inch telescope, which is expected to start action two or three years hence, the image-slicer may help clear up the mystery of the Expanding Universe. Dr. Hubble, who collected most of the evidence for expansion (high-velocity retreat of the distant nebulae), now believes that after traveling long distances something in the nature of light may cause merely an appearance of expansion, that the universe may well be actually static. Others-- notably Harvard's Shapley and England's Eddington--disagree with him.

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