Star Dust Blue

When Professor Auguste Piccard floated back to earth from the stratosphere, he reported that the sky up there was deep, dark blue in daytime (TIME, June 8, 1931). Last week, floating down from a flight of logic. Astronomer Otto Struve of Yerkes Observatory declared in the Astrophysical Journal that the universal sky should not be dark, day or night. It should be light blue. Starlight striking star dust should make the general illumination of cosmic space as blue as the daylight sky seen from the surface of Earth. If Professor Piccard makes his proposed flight from Chicago next July, he will have Dr. Struve's purely calculated vision of the empyrean to controvert.

Stars look redder than most astrophysical criteria indicate that they actually are. This apparent astral rubrication might be due to 1) the speeding of stars away from Earth (the Doppler effect of lengthening waves) or 2) the scattering of starlight by star dust and star gases which permeate space.

The sun looks redder at sundown than at noon because its light traverses a thicker layer of air at evening and is scattered by more particles in the atmosphere. The light lost by scattering reappears as the blue of the sky. It exactly compensates for the redness of direct sunlight.

The real light of a star minus its apparent, reddened light is both a measure of the blue light lost into particles of matter between the stars and a measure of the number of such particles. From these factors Dr. Struve calculates there is not more than one particle of star dust in each 15 cu. in. of interstellar space. If that is so, then all the star dust along the 25-million-million-mile line between Earth and Proxima Centauri, nearest star except the Sun, could be packed in a half-inch cube.

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