γ of Andromeda is a magnificent double orb, to which we shall return in the next chapter, i.e., the telescope resolves it into two marvelous suns, one of which is topaz-yellow, and the other emerald-green. Three stars, indeed, are visible with more powerful instruments.
Fig. 7.—Perseus, the Pleiades, Capella.
Above β and near a small star, is visible a faint, whitish, luminous trail: this is the oblong nebula of Andromeda, the first mentioned in the history of astronomy, and one of the most beautiful in the Heavens, perceptible to the unaided eye on very clear nights.
The stars α, β and γ of Perseus form a concave bow which will serve in a new orientation. If it is prolonged in the direction of δ, we find a very brilliant star of the first magnitude. This is Capella, the Goat, in the constellation of the Charioteer (Fig. 7).
If coming back to δ in Perseus, a line is drawn toward the South, we reach the Pleiades, a gorgeous cluster of stars, scintillating like the finest dust of diamonds, on the shoulder of the Bull, to which we shall come shortly, in studying the Constellations of the Zodiac.
Not far off is a very curious star, β of Perseus, or Algol, which forms a little triangle with two others smaller than itself. This star is peculiar in that, instead of shining with a fixed light, it varies in intensity, and is sometimes pale, sometimes brilliant. It belongs to the category of variable stars which we shall study later on. All the observations made on it for more than two hundred years go to prove that a dark star revolves round this sun, almost in the plane of our line of sight, producing as it passes in front of it a partial eclipse that reduces it from the second to the fourth magnitude, every other two days, twenty hours, and forty-nine minutes.
And now, let us return to the Great Bear, which aided us so beneficently to start for these distant shores, and whence we shall set out afresh in search of other constellations.
If we produce the curved line of the tail, or handle, we encounter a magnificent golden-yellow star, a splendid sun of dazzling brilliancy: let us make our bow to Arcturus, α of the Herdsman, which is at the extremity of this pentagonal constellation. The principal stars of this asterism are of the third magnitude, with the exception of α, which is of the first. Alongside of the Herdsman is a circle consisting of five stars of the third and fourth magnitude, save the third, α, or the Pearl, which is of the second magnitude. This is the Corona Borealis. It is very easily recognized (Fig. 8).
