Part 37

The telescope shows that the Galaxy arises from the light of countless stars too minute to be separately visible with the naked eye. The telescopic stars, instead of being uniformly distributed over the celestial sphere, are mostly condensed in the region of the Galaxy. They are fewest in the regions most distant from this belt, and become thicker as we approach it. The greater the telescopic power, the more marked is the condensation. With the naked eye the condensation is hardly noticeable; but with the aid of a very small telescope, we see a decided thickening of the stars in and near the Galaxy, while the most powerful telescopes show that a large majority of the stars lie actually in the Galaxy. If all the stars visible with a twelve-inch telescope were blotted out, we should find that the greater part of those remaining were in the Galaxy.

The increase in the number of the stars of all magnitudes as we approach the plane of the Milky-Way is shown in Fig. 368. The curve acb shows by its height the distribution of the stars above the ninth magnitude, and the curve ACB those of all magnitudes.

327. Star-Clusters.--Besides this gradual and regular condensation towards the Galaxy, occasional aggregations of stars into clusters may be seen. Some of these are visible to the naked eye, sometimes as separate stars, like the "Seven Stars," or Pleiades, but more commonly as patches of diffused light, the stars being too small to be seen separately. The number visible in powerful telescopes is, however, much greater. Sometimes hundreds or even thousands of stars are visible in the field of view at once, and sometimes the number is so great that they cannot be counted.

328. Nebulæ.--Another class of objects which are found in the celestial spaces are irregular masses of soft, cloudy light, known as nebulæ. Many objects which look like nebulæ in small telescopes are shown by more powerful instruments to be really star-clusters. But many of these objects are not composed of stars at all, being immense masses of gaseous matter.

The general distribution of nebulæ is the reverse of that of the stars. Nebulæ are thickest where stars are thinnest. While stars are most numerous in the region of the Milky-Way, nebulæ are most abundant about the poles of the Milky-Way. This condensation of nebulæ about the poles of the Milky-Way is shown in Figs. 367 and 369, in which the points represent, not stars, but nebulæ.

II. THE STARS.

The Constellations.

329. The Great Bear.--The Great Bear, or Ursa Major, is one of the circumpolar constellations (4), and contains one of the most familiar asterisms, or groups of stars, in our sky; namely, the Great Dipper, or Charles's Wain. The positions and names of the seven prominent stars in it are shown in Fig. 370. The two stars Alpha and Beta are called the Pointers. This asterism is sometimes called the Butcher's Cleaver. The whole constellation is shown in Fig. 371. A rather faint star marks the nose of the bear, and three equidistant pairs of faint stars mark his feet.

330. The Little Bear, Draco, and Cassiopeia.--These are all circumpolar constellations. The most important star of the Little Bear, or Ursa Minor, is Polaris, or the Pole Star. This star may be found by drawing a line from Beta to Alpha of the Dipper, and prolonging it as shown in Fig. 372. This explains why these stars are called the Pointers. The Pole Star, with the six other chief stars of the Little Bear, form an asterism called the Little Dipper. These six stars are joined with Polaris by a dotted line in Fig. 372.

The stars in a serpentine line between the two Dippers are the chief stars of Draco, or the Dragon; the trapezium marking its head. Fig. 373 shows the constellations of Ursa Minor and Draco as usually figured.

To find Cassiopeia, draw a line from Delta of the Dipper to Polaris, and prolong it about an equal distance beyond, as shown in Fig. 372. This line will pass near Alpha of Cassiopeia. The five principal stars of this constellation form an irregular W, opening towards the pole. Between Cassiopeia and Draco are five rather faint stars, which form an irregular K. These are the principal stars of the constellation Cepheus. These two constellations are shown in Fig. 374.

331. The Lion, Berenice's Hair, and the Hunting-Dogs.--A line drawn from Alpha to Beta of the Dipper, and prolonged as shown in Fig. 375, will pass between the two stars Denebola and Regulus of Leo, or the Lion. Regulus forms a sickle with several other faint stars, and marks the heart of the lion. Denebola is at the apex of a right-angled triangle, which it forms with two other stars, and marks the end of the lion's tail. This constellation is visible in the evening from February to July, and is figured in Fig. 376.

In a straight line between Denebola and Eta, at the end of the Great Bear's tail, are, at about equal distances, the two small constellations of Coma Berenices, or Berenice's Hair, and Canes Venatici, or the Hunting-Dogs. These are shown in Fig. 377. The dogs are represented as pursuing the bear, urged on by the huntsman Boötes.

332. Boötes, Hercules, and the Northern Crown.--Arcturus, the principal star of Boötes, may be found by drawing a line from Zeta to Eta of the Dipper, and then prolonging it with a slight bend, as shown in Fig. 378. Arcturus and Polaris form a large isosceles triangle with a first-magnitude star called Vega. This triangle encloses at one corner the principal stars of Boötes, and the head of the Dragon near the opposite side. The side running from Arcturus to Vega passes through Corona Borealis, or the Northern Crown, and the body of Hercules, which is marked by a quadrilateral of four stars.

Boötes, who is often represented as a husbandman, Corona Borealis, and Hercules, are delineated in Fig. 379. These constellations are visible in the evening from May to September.

333. The Lyre, the Swan, the Eagle, and the Dolphin.--Altair, the principal star of Aquila, or the Eagle, lies on the opposite side of the Milky-Way from Vega. Altair is a first-magnitude star, and has a faint star on each side of it, as shown in Fig. 380. Vega, also of the first magnitude, is the principal star of Lyra, or the Lyre. Between these two stars, and a little farther to the north, are several stars arranged in the form of an immense cross. The bright star at the head of this cross is called Deneb. The cross lies in the Milky-Way, and contains the chief stars of the constellation Cygnus, or the Swan. A little to the north of Altair are four stars in the form of a diamond. This asterism is popularly known as Job's Coffin. These four stars are the chief stars of Delphinus, or the Dolphin. These four constellations are shown together in Fig. 381. The Swan is visible from June to December, in the evening.

334. Virgo.--A line drawn from Alpha to Gamma of the Dipper, and prolonged with a slight bend at Gamma, will reach to a first-magnitude star called Spica (Fig. 382). This is the chief star of the constellation Virgo, or the Virgin, and forms a large isosceles triangle with Arcturus and Denebola.

Virgo is represented in Fig. 383. To the right of this constellation, as shown in the figure, there are four stars which form a trapezium, and mark the constellation Corvus, or the Crow. This bird is represented as standing on the body of Hydra, or the Water-Snake. Virgo is visible in the evening, from April to August.

335. The Twins.--A line drawn from Delta to Beta of the Dipper, and prolonged as shown in Fig. 384, passes between two bright stars called Castor and Pollux. The latter of these is usually reckoned as a first-magnitude star. These are the principal stars of the constellation Gemini, or the Twins, which is shown in Fig. 385. The constellation Canis Minor, or the Little Dog, is shown in the lower part of the figure. There are two conspicuous stars in this constellation, the brightest of which is of the first magnitude, and called Procyon.

The region to which we have now been brought is the richest of the northern sky, containing no less than seven first-magnitude stars. These are Sirius, Procyon, Pollux, Capella, Aldebaran, Betelgeuse, and Rigel. They are shown in Fig. 386.

Betelgeuse and Rigel are in the constellation Orion, being about equally distant to the north and south from the three stars forming the belt of Orion. Betelgeuse is a red star. Sirius is the brightest star in the heavens, and belongs to the constellation Canis Major, or the Great Dog. It lies to the east of the belt of Orion. Aldebaran lies at about the same distance to the west of the belt. It is a red star, and belongs to the constellation Taurus, or the Bull. Capella is in the constellation Auriga, or the Wagoner. These stars are visible in the evening, from about December to April.

336. Orion and his Dogs, and Taurus.--Orion and his Dogs are shown in Fig. 387, and Orion and Taurus in Fig. 388. Aldebaran marks one of the eyes of the bull, and is often called the Bull's Eye. The irregular V in the face of the bull is called the Hyades, and the cluster on the shoulder the Pleiades.

337. The Wagoner.--The constellation Auriga, or the Wagoner (sometimes called the Charioteer), is shown in Fig. 389. Capella marks the Goat, which he is represented as carrying on his back, and the little right-angled triangle of stars near it the Kids. The five chief stars of this constellation form a large, irregular pentagon. Gamma of Auriga is also Beta of Taurus, and marks one of the horns of the Bull.

338. Pegasus, Andromeda, and Perseus.--A line drawn from Polaris near to Beta of Cassiopeia will lead to a bright second-magnitude star at one corner of a large square (Fig. 390). Alpha belongs both to the Square of Pegasus and to Andromeda. Beta and Gamma, which are connected with Alpha in the figure by a dotted line, also belong to Andromeda. Algol, which forms, with the last-named stars and with the Square of Pegasus, an asterism similar in configuration to the Great Dipper, belongs to Perseus. Algenib, which is reached by bending the line at Gamma in the opposite direction, is the principal star of Perseus.

Pegasus is shown in Fig. 391, and Andromeda in Fig. 392. Cetus, the Whale, or the Sea Monster, shown in Fig. 393, belongs to the same mythological group of constellations.

339. Scorpio, Sagittarius, and Ophiuchus.--During the summer months a brilliant constellation is visible, called Scorpio, or the Scorpion. The configuration of the chief stars of this constellation is shown in Fig. 394. They bear some resemblance to a boy's kite. The brightest star is of the first magnitude, and called Antares (from anti, instead of, and Ares, the Greek name of Mars), because it rivals Mars in redness. The stars in the tail of the Scorpion are visible in our latitude only under very favorable circumstances. This constellation is shown in Fig. 395, together with Sagittarius and Ophiuchus. Sagittarius, or the Archer, is to the east of Scorpio. It contains no bright stars, but is easily recognized from the fact that five of its principal stars form the outline of an inverted dipper, which, from the fact of its being partly in the Milky-Way, is often called the Milk Dipper.

Ophiuchus, or the Serpent-Bearer, is a large constellation, filling all the space between the head of Hercules and Scorpio. It is difficult to trace, since it contains no very brilliant stars. This constellation and Libra, or the Balances, which is the zodiacal constellation to the west of Scorpio, are shown in Fig. 396.

340. Capricornus, Aquarius, and the Southern Fish.--The two zodiacal constellations to the east of Sagittarius are Capricornus and Aquarius. Capricornus contains three pairs of small stars, which mark the head, the tail, and the knees of the animal.