Cancer has no conspicuous stars, and it covers but a small space on the sky, yet as a constellation it is as old as any, and it has given us our “Tropic of Cancer,” because in ancient times, before the Precession of the Equinoxes had drifted the zodiacal signs and constellations apart, the place of the Summer Solstice, where the sun is at its northern extreme of declination, was situated in Cancer, though now we find it in Gemini, close to the borders of Taurus.
Westward from Cancer we see the great group of mighty stars and constellations of which Orion is the chief and centre, but Sirius the brightest jewel. They are now declining rapidly toward the horizon, and will be better studied at another season. They include, besides Orion, Gemini, Auriga, Taurus, Canis Major, and Canis Minor, and will be found more favorably situated in the chart devoted to the sky at the Winter Solstice. For the present, then, we turn our eyes to the northern central part of the vernal heavens. There, almost overhead, shines the “Great Bear,” Ursa Major, always recognizable by the remarkable figure of the “Great Dipper,” or, as they prefer to call it in Old England—where brimming dippers of sparkling water lifted dripping from the “old oaken bucket” are not so familiar as in New England—the “Wain,” or the “Plough.” We have already remarked that at this season the Bear has his feet uppermost in the middle of the sky and his back downward toward the pole. The Dipper, too, is now upside down, drained of its last imaginary drop, though its stars may be the more brilliant for that. The figure of the bowl is situated on the flank of the Bear, and its handle represents his impossible tail. Six of its stars are of the second magnitude, and one, at the junction of the bowl and the handle, of the third. Their Greek letters, beginning at the northwestern corner of the bowl, are, Alpha (α), Beta (β), Gamma (γ), Delta (δ), Epsilon (ε), Zeta (ζ), and Eta (η), and their names, in the same order, Dubhe, Merak, Phæd, Megrez, Alioth, Mizar, and Benetnasch.
I once knew a country school-teacher who thought that he had acquired a pretty good knowledge of astronomy when he had learned these names by heart. He certainly knew more of uranography than most people. The names seem to be all of Arabic origin, and at the risk of destroying their charm I will give, from Allen’s Star Names, their probable significations. Dubhe means simply “Bear”; Merak (sometimes Mirak), “Loin”; Phæd (sometimes Phecda or Phad), “Thigh”; Megrez, “Root of the Tail”; Alioth, meaning uncertain, probably something to do with the tail; Mizar (originally Mirak), “Girdle”; and Benetnasch (sometimes Alcaid), “Chief of the Mourners,” from an Arabic phrase having that signification.
The star Megrez, now so much fainter than the others, was once as bright as any of them. It has faded within three hundred years.
Close by Mizar a fairly good eye has no difficulty in seeing a small star which is named Alcor (signification uncertain). The Arabs are said to have called these two stars the “Horse and his Rider,” and to have regarded it as a test of good vision to be able to see them both. It is certainly not a severe test at present. Mizar itself is telescopically double, presenting a beautiful sight in a small telescope, the distance asunder being about 14″. The smaller star is like an emerald in hue, and the color is usually remarked at once by the beginner in telescopic observation. The larger star is one of those strange objects called “spectroscopic binaries”—two suns locked in the embrace of gravitation and spinning round a centre so near to each other that to anything less penetrating than the magic eye of the spectroscope they appear as a single body.
Merak and Dubhe are the celebrated “Pointers,” so called because a line drawn from the former to the latter, and continued toward the pole, passes close to Polaris, the Pole-star, of which we shall presently speak. The distance between these stars is about five degrees, so that they serve as a rough measuring-stick for estimating distances in the sky. Immediately west of the meridian will be seen a curving row of stars which indicate the head of the Bear. Three of his feet, or claws, are represented by as many pairs of stars between the Great Dipper and the Sickle of Leo, one of the pairs being east of the meridian, one west of it, and one nearly upon it. Below the outer end of the handle of the Dipper, in the direction of Denebola, a fairly bright star, Cor Caroli, which English loyalty named for the heart of the unfortunate King Charles I., shines on the collar of one of the “Hunting Dogs,” Canes Venatici, which Boötes is represented as holding in a leash as he chases Ursa Major round the pole. This, too, is a beautiful double, the contrasted colors of whose widely separated stars are finely shown by a small telescope.
Now let the eye run along the curve of the Dipper’s handle, beginning at the bowl, and then, springing on, continue the same curve eastward; it will encounter, at a distance about equal to the whole length of the Dipper, a very great and brilliant star—Arcturus, brighter than Spica and Regulus, and usually, when not very far risen from the horizon, of a distinctly reddish hue. It is the chief star of Boötes, the “Driver,” the “Vociferator,” the “Herdsman,” or the “Bear-watcher,” as it has been variously rendered. We shall have more to say about Boötes in another chapter, but Arcturus is a star so splendid and famous that it cannot be passed in silence the first time the beginner catches sight of it. There is a standing dispute concerning the relative rank in brightness of Arcturus among the leading stars of the northern hemisphere. Its principal rivals are Vega in the Lyre, and Capella in Auriga. But all three differ in color, and that makes it more difficult to decide upon their relative brilliance, since different eyes vary in their sensitiveness to color. The Harvard Photometric Durchmusterung gives Vega the first and Arcturus the third rank among these three; but many eyes recognize rather a pre-eminence of Arcturus. My own impression has usually been that Arcturus looms larger than either Vega or Capella, but that Vega is the most penetratingly brilliant. It is very curious to notice the effect of the colors of these stars. The sharp blue ray in the light of Vega gives it a diamond-like quality which is lacking in Capella, whose light is white with just a suspicion of amber. Arcturus is a very pale topaz when high in the sky, and a ruddy yellow, sometimes flaming red, when near the horizon. It is a thrilling recollection of the writer’s early boyhood that he felt an undefined fear of Arcturus when seen rising ominously red and flashing through the leafless boughs of an apple orchard in the late evenings of February. All the ancients feared Arcturus for its supposed influence in producing storms and bad harvests.
Arcturus is a sun of enormous magnitude, estimated all the way from one to six thousand times as great in luminosity as our sun. It is also travelling with great rapidity, its speed, according to some estimates, amounting to two or three hundred miles per second; but most of this is cross-motion with reference to us, its general direction being toward the south-southwest. If it is travelling three hundred miles per second, it would traverse the space between the sun and the nearest star, Alpha Centauri, in about three thousand years. We shall touch on Arcturus again when dealing with Boötes in the next chapter.
Disregarding for the present the exquisite circlet of Corona Borealis, the “Northern Crown,” and the quadrilateral figure in Hercules, seen northeast of Arcturus, we turn to the great dragon, Draco, whose diamond-shaped head may be seen far over in the northeast above sparkling Vega, which is just on the horizon. As a reference to the charts of the circumpolar stars at the end of the book will show, Draco is a remarkably crooked constellation, its line of stars winding round between the “Little Dipper” in Ursa Minor, which has Polaris at the end of its handle, and the “Great Dipper” of Ursa Major. Its most interesting, though not now its brightest, star is Alpha, or Thuban, Arabic for “dragon.” It lies between the end of the handle of the Great Dipper and the bowl of the small one. About forty-six hundred years ago Alpha Draconis was the Pole-star, and is believed to have shone down the long tube-like passage in the great pyramid of Cheops into the watching eyes of the priestly astronomers, assembled to view it in the mysterious chamber hollowed out of the solid rock deep under the foundations of the mighty pile. They thus had a telescope more than three hundred feet long as immovable as the solid earth, but, alas for their calculations, the star itself shifted its position, and their gigantic observing tube became useless until modern science inferred from its position the date of their building. How imposing to the imagination this association between a particular star and the mightiest structure made by human hands on the earth! Two centuries ago Thuban was more than twice as bright as it is now, and when the Egyptian priests sedulously observed it from their gloomy cavern, more than a thousand years before the magic-working days of Moses, it may have been brighter still.
Gamma (γ), or Eltanin (the “Dragon”), in the triangular head, is now the brightest star in the constellation, and it, too, has a history. Lockyer and others have identified it as the orientation star of Rameses’ great temple at Karnak, and of the temples of Hathor and Mut at Dendera and Thebes. There is something magnificent in this thought of the ancient temple-builders—to square their work by the stars, and to construct long rows of sphinxes and majestic columns to conduct a ray from the sky to the eye of the god in his dark and hidden chamber, where no impious foot dared follow.