In order to distinguish one star from another, the convention of denoting them by the letters of the Greek Alphabet has been adopted, for it would be impossible to give a name to each, so considerable is their number.[3]
α and β denote the front wheels of the Chariot generally known as the "pointers;" γ and δ the hind wheels; ε, ζ, η the three horses. All these stars are of the second order of magnitude (the specific meaning of this expression will be explained in the next chapter), except the last (δ) of the quadrilateral, which is of the third order.
Fig. 3.—The Great Bear (or Dipper), and the Pole-Star.
Figure 3 gives the outline of this primitive constellation. In revolving in twenty-four hours round the Pole, which is situated at the prolongation of a line drawn from β to α, it occupies every conceivable position,—as if this page were turned in all directions. But the relative arrangement of the seven stars remains unaltered. In contemplating these seven stars it must never be forgotten that each is a dazzling sun, a center of force and life. One of them is especially remarkable: ζ, known as Mizar to the Arabs. Those who have good sight will distinguish near it a minute star, Alcor, or the Cavalier, also called Saidak by the Arabs—that is, the Test, because it can be used as a test of vision. But further, if you have a small telescope at your disposal, direct it upon the fine star Mizar: you will be astonished at discovering two of the finest diamonds you could wish to see, with which no brilliant is comparable. There are several double stars; these we shall become acquainted with later on.
Meantime, we must not forget our celestial geography. The Great Bear will help us to find all the adjacent constellations.
Fig. 4.—To find the Pole-Star.
If a straight line is drawn (Fig. 4) from β through α, which forms the extremity of the square, and is prolonged by a quantity equal to the distance of α from the tip of the handle, we come on a star of second magnitude, which marks the extremity of a figure perfectly comparable with the Great Bear, but smaller, less brilliant, and pointing in the contrary direction. This is the Little Bear, composed, like its big brother, of seven stars; the one situated at the end of the line by which we have found it is the Pole-Star.