On a clear, moonless night, far from any city glare, a keen-eyed observer can see in the sky a faintly glowing cone. This is the "zodiacal light," which astronomers believe is sunlight reflected from dust particles revolving around the sun like microscopic planets. In Sky and Telescope, Astronomer Otto Struve of the University of California tells how he thinks the dust got there.
It was not left over from the original material out of which the planets condensed. That has long since disappeared. The smaller particles of it were blown out of the solar system by the pressure of sunlight. The larger...
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