Location.—α Persei lies on a line drawn from β to γ Andromedæ, and is about 9° from the latter. The most striking feature in Perseus is the so-called "segment of Perseus," a curve of stars beginning about 12° below Cassiopeia, and curving toward Ursa Major. Note the famous variable Algol the Demon star. It represents the Medusa's head which Perseus holds in his hand. It varies from the second to the fourth magnitude in about three and one-h
Note a dull red star near Algol, and a pretty pair just above Algenib.
An opera-glass reveals much that is worthy of observation in this region of the sky. It has been said of the clusters between Cassiopeia and Perseus that they form the most striking sidereal spectacle in the northern heavens. They are visible to the naked eye. Algenib never sets in the latitude of New York, just touching the horizon at its lower culmination. It is estimated that Algol is a little over a million miles in diameter, η has three faint stars on one side nearly in a line, and one on the other—a miniature representation of Jupiter and his satellites.
Algol, when on the meridian of New York City, is only one tenth of a degree from the zenith point. This remarkable variable has a dark companion star revolving near it obscuring its light in part from us at stated intervals. By means of the spectroscope the speed diameter and mass of this invisible star has been reckoned.