But Polaris will not continue to be the unerring guide to the north that it now is. The Precession of the Equinoxes is carrying the pole progressively westward in right ascension, so that Polaris will eventually be left far behind. But the motion of the pole is in a circle about twenty-three and a half degrees in radius, and it requires about 25,800 years to complete a revolution round this circle. Consequently, at the end of that period, Polaris will have come back to reign again as the North Star for many centuries. In the interim other stars will have occupied its place. About 11,500 years from now the brilliant Vega, or Alpha Lyræ, will be the North Star, and in about 21,000 years Alpha Draconis (Thuban) will once more shine down the great northward-pointing passage in the pyramid of Cheops, if that pyramid shall still exist. Polaris, unlike some of the others stars that we have been looking at, is running away into space instead of approaching us, at a speed which has been estimated at about 1,380,000 miles per day. Its present distance is not less than 200,000,000,000,000 miles. It has an invisible companion with which it circles in an orbit of a few million miles diameter in a period of about four days. Polaris is also a celebrated visual double. With a telescope of two or three inches aperture you can see close by its flaming rays a minute blue star, a delicately beautiful sight. In the older days of telescopes, before they had attained the perfection which improvements in glass-making and lens-shaping have rendered possible, this little companion star of Polaris was a universal test of excellence. Its prestige was historical. The amateur owner of a telescope who could see that star clearly felt a joy that he could hardly express. The old makers of object-glasses, by rule of thumb, always tried them on the companion of the Polestar as a standard test for small apertures. The small star is of the ninth magnitude, and situated about 18″.6 from its primary. The stars Beta (β), or Kochab (the “Star”), and Gamma (γ), in Ursa Minor, are called the Wardens, or Guards, of the Pole. In low northern latitudes, where these stars sweep the horizon at their lower culmination, Shakespeare’s description in _Othello_ would be literally true during a great storm at sea: “The wind-shak’d surge, with high and monstrous mane, Seems to cast water on the burning Bear And quench the guards of th’ ever-fixed pole.” The constellations Cepheus, Cassiopeia, and Perseus, now low in the northwest and north, we leave for description to another chapter. II THE EVENING SKY AT THE SUMMER SOLSTICE