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TELESCOPIC OBJECTS.

1. a AQUARII (Phard)-A star with a minute companion on the Water-bearer's left shoulder; R A. 21h. 57m. 38s.; Dec. S. 1° 05′ 07′′. A 3, pale yellow; B 18, grey; and another star in the field on a line with A and B. Markab is on a line joining Alpheraiz and Phard, and about half way between them.

2. B AQUARII (Sad-al-melik)—▲ star with a companion on the right shoulder; R. A. 21h. 23m. 07s.; Dec. N. 6° 16' 04". A 3, pale yellow; B 15, blue. A very delicate object. 8. Y AQUARII-A delicate but wide DOUBLE STAR, on the water-pot; R. A. 22h. 13m. 238.; Dec. S. 2° 11′ 05′′. A 4, greenish tinge; B 14, purple. It is about 4° east-by-south from Sad-al-melik.

4.

AQUARII-A BINARY STAR in the left wrist, about 6° east from Sadalmelik; R. A. 22h. 20m. 35s.; Dec. S. 0° 50' 02". A 4, very white; B 4%, white.

5. T'AQUARII-A fine DOUBLE STAR in the left leg, one third of the way from Fomalhaut to Pegasi; R. A. 22h. 39m. 13s.; Dec. S. 14° 53′ 09". A 6, white; B 9, pale garnet.

6. AQUARII-A DOUBLE STAR in the stream, being the first of three similar stars marked, 2, 3; R. A. 23h. 07m. 30s.; Dec. S. 9° 57′ 05′′. A 5%, orange tint; B 9, sky blue. It is about one-third of the way from Fomalhaut to a Andromeda. Several other beautiful double stars east of Scheat, in the stream, as shown on the map.

7. A FINE GLOBular cluster near the neck of Aquarius, about 5° north-half-east from B; R. A. 21h. 23m. 07s.; Dec. S. 6° 16' 04". A cluster of exceedingly small stars, which has been likened to "a heap of fine sand." Several telescopic outliers in the field. Map VIII., Fig. 66.

8. A PLANETARY NEBULA in the middle of the scarf; R. A. 20h. 55m. 27s.; Dec. S. 11' 59′ 08′′. About 12° east of a Capricorni, where a line from the Eagle's tail over Anti. noi, and as far again, reaches it. It is bright to its very dise, and but for its pale blu tint, would be a very miniature of Venus.

PISCES AUSTRALIS (THE SOUTHERN FISH).—MAP II.

238. This constellation is directly S. of Aquarius, and is represented as a fish drinking the water which Aquarius pours from his urn. Its mean declination is 31° S. and its mean right ascension and time of passing the meridian are the same as those of Aquarius, and it is seen on the meridian at the same time, viz. on the 15th of October. It contains 24 visible stars, of which one is of the 1st magnitude, or between the 1st and 2d, two are of the 3d, and five of the 4th. The first and most beautiful of all is Fomalhuut, situated in the mouth. This is 14° directly S. of Scheat in Aquarius, and may be seen passing the meridian low down in the southern hemisphere, on the 22d and 23d of October. Its position in the heavens has been determined with the greatest possible accuracy, to enable navigators to find their longitude at sea.

The mode of doing this cannot be explained here. The problem is one of some difficulty. It consists in finding the angular distance between some star whose position is well known,

TELESCOPIC OBJECTS.-Alpha? Beta? Gamma? Zeta? Tau? Psi? What clusters, and where shown on the map? What nebula?

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238. Situation of Pisces Australis? How represented? When on the meridian? ber of stars? Magnitude? The principal star? How situated? What use made of it? What said of the method of finding the longitude by the moon and stars?

and the moon when she is passing near it; also, the altitude of each, at the same instaut with good sextants. These data furnish the elements of a spherical triangle, the solution of which, after various intricate corrections, is made to result in the longitude of the given place. See note to Arietes. In 1714, the British Parliament offered a reward of 10,000 pounds sterling, to any man who should discover a method of determining the longitude within 1°, or 60 geographical miles of the truth; 15,000 pounds to the man who shouid find it within 40 miles, and 20,000 pounds, if found within 30 miles. These rewards in part, have been since distributed among eminent mathematicians, in Europe, agreeably to the respective merits of their discoveries.

HISTORY.

This constellation is supposed to have taken its name from the transformation of Venus into the shape of a fish, when she fled, terrified at the horrible advances of the monster Typhon, as we have related in the mythology of the Fishes.-(See Pisces.)

TELESCOPIC OBJECTS.

a PISCES AUSTRALIS-A first magnitude star with a very distant companion, in the eyc of the fish; R. A. 22h. 48m. 48s.; Dec. S. 80° 28′ 03′′. A 1, reddish; B 91⁄2, dusky blue.

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LACERTA (THE LIZARD).—MAP II.

239. This is a small and obscure modern constellation, between the tail of Cygnus and the head of Andromeda. It has one star of the 4th magnitude, eight of the 5th, and a few much smaller.

240. Between Lacerta and Andromeda a singular looking figure appears on the map, called Gloria Frederica; or Frederic's Glory. It was inserted among the constellations by Bode, in 1787, as a compliment to Frederic II., of Prussia. It consists of a crown, a laurel, a sword, and a pen, to represent the monarch, the hero, the sage, and the pacificator. But the constellation was not recognized by astronomers, and, as such, has already passed from the heavens.

TELESCOPIC OBJECTS.

1. A neat DOUBLE STAR on the tip of the Lizard's tail; R. A. 22h. 11m. 56s.; Dec. N. 86° 58′ 01′′. A 6%, pale white; B 9, livid.

2. A delicate but wide DOUBLE STAR on the shoulder; R. A. 22h. 14m. 25s.; Dec. N. 45° 43' 09. A 5, pale yellow; B 13, orange tint. A line from Polaris carried by the east of Cepheus tiara, and 11° further, will find it the lucida of a fine galaxy field.

8. A WIDE DOUBLE STAR near the end of the tail, the southern star of three forming a neat triangle; R. A. 22h. 32m. 05s.; Dec. N. 38° 18′ 2′′. A 6%, white; B 10, violet.

4. A DELICATE TRIPLE STAR in the space between the Lizard's back and the left hand of Andromeda; R. A. 22h. 49m. 06s.; Dec. N. 40° 45' 1". A 6, bright white; B. 15, pale blue; C 9%, reddish; a fourth star at a distance. A very difficult object; claimed by some for Andromeda, but usually classed as belonging to the Lizard.

HISTORY.-Supposed origin of this constellation?

TELESCOPIC OBJECTS.-Alpha? Where situated?

239. Describe Lacerta.

Where situated? 240. What other small constellation near? By whom inserted, when and why? Of what does it consist? To represent what? Is it recognized by astronomers?

TELESCOPIC OBJECTS.-What double stars in Lacerta? What triple star? Quadruple? Cluster? Any of them shown on the map?

5. A QUADRUPLE STAR, the western one of the three forming the triangle at the end of the tail; R. A. 22h. 29mn. 46s.; Dec. N. 38° 48' 5". About 20° northwest of Alpheratz. A and B 6, both white; C 11, greenish; D 10, blue.

6. A LARGE LOOSE CLUSTER in the Lizard's mouth; R. A. zh. 08m. 59s.; Dec. N. 49° 05' 1. Stars from the 9th to the 14th magnitudes. A line carried from Polaris through the tiara of Cepheus, and 8° beyond, strikes it.

CHAPTER

XIII.

VARIABLE AND DOUBLE STARS-CLUSTERS AND NEBULA.

241. THE periodical variations of brilliancy to which some of the fixed stars are subject, may be reckoned among the most remarkable of their phenomena. Several stars, formerly distinguished by their splendor, have entirely disappeared; others are now conspicuous which do not seem to have been visible to the ancient observers; and there are some which alternately appear and disappear, or, at least, of which the light undergoes great periodic changes. Some seem to become gradually more obscure, as Delta in the Great Bear; others, like Beta in the Whale, to be increasing in brilliancy.

242. Some stars have all at once blazed forth with great splendor, and, after a gradual diminution of their light, again become extinct. The most remarkable instance of this kind is that of the star which appeared in 1572, in the time of Tycho Brahe. It suddenly shone forth in the constellation Cassiopeia, with a splendor exceeding that of stars of the first magnitude, even of Jupiter and of Venus, at their least distances from the earth; and could be seen with the naked eye, on the meridian, in full day! Its brilliancy gradually diminished from the time of its first appearance, and at the end of sixteen months it entirely disappeared, and has never been seen since. (See a more particular account of this phenomenon, page 35.)

Another instance of the same kind was observed in 1604, when a star of the first magnitude suddenly appeared in the right foot of Ophiuchus. It presented, like the former, all the phenomena of a prodigious flame, being, at first, of a dazzling white, then of a reddish yellow, and, lastly, of a leaden paleness; in which its light expired. These instances prove that the stars are subject to great physical revolutions. (Page 00)

243. A great number of stars have been observed whose light seems to undergo a regular periodic increase and diminution.

241. What said of the periodical variations of the stars? 242. What other remarkable phenomenon? What instances cited? What do these instances prove? 243. What

They are properly called Variable Stars. One in the Whale has a period of 344 days ad is remarkable for the magnitude of its variations. From being a star of the second magnitude, it becomes so dim as to be seen with difficulty through powerful telescopes. Some are remarkable for the shortness of the period of their variation. Algol has a period of between two and three days; Delta Cephei, of 5 days; Beta Lyra, of 6 2-5 days; and Mu Antinoi, of 7 days.

The regular succession of these variations precludes the supposition of an actual destruction of the stars; neither can the variations be supposed to arise from a change of distance; for, as the stars invariably retain their apparent places, it would be necessary to suppose that they approach to, and recede from the earth in straight lines, which is very improbable. The most probable supposition is, that the stars revolve, like the sun and planets, about an axis. "Such a motion," says the elder Herschel, "may be as evidently proved, as the diurnal motion of the earth. Dark spots, or large portions of the surface, less luminous than the rest, turned alternately in certain directions, either toward or from us, will account for all the phenomena of periodical changes in the luster of the stars, so satisfactorily, that we certainly need not look for any other cause."

DOUBLE STARS.

244. On examining the stars with telescopes of considerable power, many of them are found to be composed of two or more stars, placed contiguous to each other, or of which the distance subtends a very minute angle. This appearance is, probably, in many cases, owing solely to the optical effect of their position relative to the spectator; for it is evident that two stars will appear contiguous if they are placed nearly in the same line of vision, although their real distance may be immeasurably great,

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Here the observer on the left sees a large and small star at A, apparently near toge ther-the lowest star being much the smallest. But instead of their being situated as iney appear to be, with respect to each other, the true position of the smaller star may be at B instead of A; and the difference in their apparent magnitudes may be wholly owing to the greater distance of the lower star.

Upon this subject Dr. Herschel remarks, that this nearness of the stars to each other, in certain cases, might be attributed to some accidental cause, did it occur only in a few instances; but the frequency of this companionship, the extreme closeness, and, in many cases, the near equality of the stars so conjoined, would alone lead to a strong suspicion of a more near and intimate relation than mere casual juxtaposition.

245. There are, however, many instances in which the angle of position of the two stars varies in such a manner as to indi

are these unsteady stars called? What specimens referred to, and their periods? What does this regular succession, &c., prove? What theory did Dr. Herschel adopt respecting the variable stars? 244. What said of double stars? Are they always really near each other? Illustrate on blackboard. Remark of Dr. Herschel? 245. Are they

cate a revolution about each other and about a common unter. In this case they are said to form a Binary system performing to each other the office of sun and planet, and are connected together by laws of gravitation like those which prevail in the solar system.

The recent observations of Sir John Herschel and Sir James South, have established the truth of this singular fact beyond a doubt. Motions have been detected, so rapid as to become measurable within very short periods of time; and at certain epochs, the satellite or feebler star has been observed to disappear, either passing behind or before the primary, or approaching so near to it that its light has been absorbed by that of the other.

246. The most remarkable instance of a regular revolution of this sort, is that of Mizar, in the tail of the Great Bear; in which the angular motion is 6 degrees and 24 minutes of a great circle, annually; so that the two stars complete a revolution about one another in the space of 584 years. About eleven twelfths of a complete circuit have been already described since its discovery in 1781, the same year in which the planet Herschel was discovered.

A double star in Ophiuchus presents a similar phenomenon, and the satellite has a motion in its orbit still more rapid. Castor in the Twins, Gamma Virginis, Zeta in the Crab, Zi Bootis, Delta Serpentis, and that remarkable double star 61 Cygni, together with several others, amounting to 40 in number, exhibit the same evidence of a revolution about each other and about a common center. (For a more particular description of these stars, see Telescopic Objects and the Map.)

But it is to be remembered that these are not the revolutions of bodies of a planetary nature around a solar center, but of sun around sun-each, perhaps, accompanied by its train of planets, and their satellites, closely shrouded from our view by the splendor of their respective suns, and crowded into a space bearing hardly a greater proportion to the enormous interval which separates them, than the distances of the satellites of our planets from their primaries bear to their distances from the sun itself.

247. The examination of double stars was first undertaken by the late Sir William Herschel, with a view to the question of parallax. His attention was, however, soon arrested by the new and unexpected phenomena which these bodies presented.

Sir William observed of them, in all, 2400. Sir James South and Herschel have given a catalogue of 380 in the Transactions of the Royal Society for 1824, and South added 455 in 1826. Sir John Herschel, in addition to the above, published an account of 1000, before he left England for the Cape of Good Hope, where he went to push his discoveries in the southern hemisphere. Professor Struve, with the great Dorpat telescope, has given a catalogue of 3,063 of the most remarkable of these stars.

The object of these catalogues is not merely to fix the place of the star within such limits us will enable us easily to discover it at any future time, but also to record a description

What do these constitute? Is it certain 246. What remarkable Period? What other binary systems? 247. Who first undertook the examination

ever really near each other? What motion?
that stars are ever thus in motion around a common center?
nstance cited? Its annual angular motion?
Are these planetary systems like our own?

of the double stars, and with what view? What number did he observe? What cata

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