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A Star That Breathes, the Milky Way

Beta Cephei, the mysterious Milky Way star which expands and contracts as though it were breathing, at last has a biography.

A summary of known facts concerning the star, interpreted in the light of recent observations at the Lick Observatory at the University of California was completed recently by H. S. Mendenhall, graduate student.

Mendenhall's interpretations were said to lend weight to the theory that Beta Cephei is contracting and expanding once in every four and one-half hours. This is such a terrific rate of speed from a terrestrial point of view that it appears to be moving toward and away from the earth at a velocity reaching a maximum of about nine and one-half miles per second.

Beta Cephei is a variable star in the Constellation Cepheus. It is best visible in the northern sky during July or August. Its distance from the earth is estimated roughly at 2,000,000,000,000,000 miles, and Mendenhall estimates its diameter at almost 2,000,000 miles, more than twice that of the sun.

In addition to the apparent velocity caused by contraction and expansion of its surface five times a day, Beta Cephei seems to have another motion. This was said by Mendenhall to be a rotation around some other star in a period of 20 years. Velocity of this rotation is something over three miles a second.

Variable stars are of particular interest to astronomers because the light from them pulsates regularly, flaring and dying as though fuel were replenished at regular intervals. The rate of this pulsation has been found to be a measure to the candle power of the star. Its distance then can be determined by contrasting its actual candle power with the apparent magnitude as seen from the earth.