Page images
PDF
EPUB

The Lambda, in Orion, is quadruple. More properly, it is a double star with two stars at a small distance. The double star is unequal; the largest white, the smallest a pale rose color.

A catalogue of the principal double stars may be seen in Dr. Brewster's supplement to Ferguson. Its insertion here would far exceed the limits designed for this compend.

Several stars have appeared for a time in the heavens, and then disappeared. In ancient catalogues, stars are enumerated, which are not now to be seen, even by the powerful instruments of modern astronomy. Others are now visible, which seem not to have been noticed by the ancients.

A new star was discovered by Cornelius Gemma, in 1572, in the chair of Cassiopeia. It surpassed Sirius in brightness and magnitude. To some eyes it appeared larger than Jupiter; and might be seen at mid-day. It afterwards gradually decreased, and, after sixteen months, entirely disappeared.

In 1596, the Stella Mira, or wonderful star, in the neck of the whale, was observed by Fabricius. It seemed alternately to vanish and reappear seven times in six years. During this time, however, it is said never to have been entirely extinct.

In 1600, a changeable star, in the neck of the Swan, was observed by Jansenius. The same was observed, and its place determined, by Kepler. It was seen by Riciolus, in 1616, 1621, and 1624. But, from 1640 to 1650, it was invisible. It had several instances of appearing and again vanishing, prior to the year 1715; when it re-appeared as a star of the sixth magnitude, its present appearance.

In 1604, a new star was discovered by Kepler and some of his friends near the head of Serpentarius. It exhibited a bright and sparkling appearance, beyond any they had before seen. Assuming the different colors of the rainbow, it appeared every moment changing, ex

cept near the horizon, where it generally appeared white. It was near Jupiter in October of that year, and surpassed that planet in magnitude, but disappeared before the following February.

Several other stars have appeared, vanished, and reappeared; some of them in regular succession. Such changeable stars may be suns, having extensive spots. Stars of this kind, by a regular rotation on their axes, may alternately present their dark and luminous sides. Maupertuis is of opinion, that some stars, by their prodigious quick rotation on their axes, may not only assume the figure of oblate spheroids, but, by their great centrifugal force, arising from such rotation, they may become of the figure of millstones, or reduced to flat circular plates, so as to be quite invisible, when their edges are turned towards us; as Saturn's ring is in such positions. But when any eccentric planets or comets go round any flat star, in orbits much inclined to its equator, the attraction of the planets or comets, in their perihelia, must alter the inclinations of that star; on which account it will appear more or less large and luminous, as its broad side is more or less turned towards us.' Ferguson.

[ocr errors]

The propriety of the term fixed, as applied to the stars, seems rendered at least doubtful by the observations of modern astronomers. An advancement of the solar system, in absolute space, is now considered certain. It was observed by Halley and Cassini. The first explanation of it was given by Mayer. But, to point out the region in the heavens to which the solar system is advancing, was reserved to Dr. Herschel. "He has examined this subject with his usual success, and has certainly discovered the direction in which our system is gradually advancing. He found that the apparent proper motion of about forty-four stars out of fifty-six, is very nearly in the direction which would result from a motion of the Sun towards the constellation Hercules, or, more accurately, to a place in the heavens,

whose right ascension is 250° 52′ 30′′, and whose north polar distance is 40° 22'."

The stars, according to their magnitude, have been arranged into six classes or orders. The largest are called stars of the first magnitude; next to these are those of the second magnitude; thus decreasing to the sixth. Of course, the least stars belong to the sixth magnitude. Sometimes, however, in modern, and even popular works, we find allusion to stars of the seventh or eighth magnitude. Considerable difference may be perceived in stars of the same class, some being much larger and more brilliant than others.

The arrangement of stars into magnitudes, was made long before the invention of telescopes. Stars unseen without the assistance of these, are called telescopic

stars.

Another happy arrangement of the stars has been handed down to us from great antiquity. By a powerful imagination, the early cultivators of astronomy conceived companies of stars as having the form of certain animals, or other sensible objects; and hence they divided the starry sphere into constellations, each including stars of different magnitudes. According as the forms appeared to their imagination, they applied names to the different constellations. Thus one constellation was called Leo, another Boötes, and another Orion. Stars not included in any constellation are called unformed stars.

The animal, or other object of each constellation, is represented on the celestial globe, and the proportion of the stars belonging to each, denoted by the letters of the Greek alphabet, according to the plan adopted by Bayer, a German, in his Uranometria, a large celestial atlas. Thus, the largest star of the constellation is denoted by Alpha, the second by Beta, the third by Gamma, and thus on in alphabetical order.

The classing of stars, however chimerical, is of vast importance, as it enables the astronomer to designate the

place of a star, a planet or a comet, at any time, as easily as a geographer can that of a hamlet or a town.

In Plate vii, figures 1, 2, 3, 4, and 5, may be seen Cygnus, the Swan; Phenix, the Phenix; Piscis Australis, the Southern Fish; Leo, the Lion; and Crux, the Cross, contracted in size from the same on a common celestial globe. From these the student may form some idea of that imagination, by which the stars were arranged into constellations. Probably in Leo, or any other constellation viewed in the heavens, he will discover but little similarity between the figure presented by the stars, and the animal or other object by which they are represented.

Forty-eight of the constellations are reckoned ancient. Of these, 12 are in the zodiac, 21 to the north, and 15 to the south of it. The whole number of constellations has been reckoned 92. Of these, 12 are in the zodiac, 35 are north, and 45 south of that circle.

In each part of the following table, the ancient constellations are placed first.

[blocks in formation]

Prior, in his Lectures, makes the whole number of constellations 105; 12 in the zodiac, 38 north, 55 south. But it may be doubted, whether increasing the number of constellations, by the addition of those that are small and unimpor tant, can be beneficial to the student in understanding the geography of the heavens.

« PreviousContinue »