ASTRONOMY
ASTRONOMY (from [ Greek ], a star, and [ Greek ], to classify or arrange) is the science which, deals with the distribution, motions, and characteristics of the heavenly bodies. It is here treated of under two heads : first, the History of Astronomy; and, secondly, Theoretical Astronomy, in which the different theories of the motions of the celestial bodies are explained, and such facts described as observation has made known respecting their nature and constitution.
Part I.—History of Astronomy.
Astronomy may probably be regarded as the most ancient of the sciences. Even the least civilised races must have recognised the regular vicissitudes of day and night (and, therefore, the diurnal course of the sun), while before long the variety and succession of the seasons would be noted, and their cause the oblique annual motion of the same luminary would be recognised. The moon in the sun s absence is so conspicuous and so useful that her motions, her various phases, and her regular disappearance and return after equal intervals of time, must have been watched in the earliest times with attention and interest. The occurrence of eclipses and other unusual phenomena would stimulate closer scrutiny. The spectacle of the starry heavens, seemingly unchangeable, save for the motions of a few wandering orbs along a certain zone of the star-sphere, early suggested an association between the fates of men and nations and these emblems of unchanging destiny on the one hand and of the changeful lot of mankind on the other. Thus astrology had its origin, a superstition which bore the same relation to astronomy that alchemy bore to chemistry. Like alchemy, astrology was of service superstition though it was in encouraging observation and in leading to discoveries of interest.
But though mankind were probably first impelled by motives of mere curiosity to observe the courses of the stars, no great length of time could have elapsed ere they perceived that the regular and uniform revolutions of the heavens might be rendered subservient to their own wants and con- veniencies. By the help of the stars the shepherd, during the night, could count the hours, the traveller track his course through the uniform wastes of the desert, and the mariner guide his bark over the ocean: the husbandman, also, learned to regulate his labours by the appearance of certain constel lations, which gave him warning of the approaching seasons. The indications derived from the simple observation of such phenomena were doubtless extremely vague ; but as civilisation advanced, the necessity of determining accurately the length of the solar year and of the lunar month, in order to regulate the calendar and the religious festivals, led to the accumulation and comparison of different observations, whereby errors were gradually diminished, and the foundations laid of a more perfect science.
Astronomy thus presenting so many objects of curiosity and interest, and having so many practical uses, could not fail to be one of the sciences first cultivated by mankind. Its origin is, consequently, hid amidst the obscurity of remote ages, and is, in fact, coeval with the earliest development of the human intellect. The records or traditions of almost every ancient nation furnish some traces of attention to the state of the heavens, and of some rude attempts to discover the laws, the order, and the period of the most remarkable phenomena, such as eclipses of the sun and moon, the motions of the planets, and the heliacal risings of the princi pal stars and constellations. The Chaldeans and Egyptians, Chinese and Indians, Gauls and Peruvians, equally regard themselves as the founders of astronomy, an honour, however, of which Josephus deprives them all, in order to ascribe it to the antediluvian patriarchs. The fables relating to the two columns of brick and marble which these sages are said to have erected, and on which they engraved the elements of their astronomy, to preserve them from the universal destruction by fire and water to which they are said to have learned from Adam the earth was doomed, are not worth the trouble of repetition ; nor is there any better proof than the assertion of that credulous historian, of their acquaintance with the minus magnus, the astronomical cycle of 600 years, which brings back the sun and moon to the same points of the heavens so nearly, that its discovery implies a pretty correct know ledge of the solar and lunar motions. Passing over those details of traditional observations or unimportant facts, we proceed to give a brief account of the state of astronomy among some early nations who have undoubtedly con tributed to the improvement of the science, or who, at least, have transmitted to future ages some records of their astronomical labours.
Astronomy of the Chaldeans, Egyptians, Phoenicians, Chinese, and Indians.
According to the unanimous testimony of the Greek historians, the earliest traces of astronomical science are to be met with among the Chaldeans and Egyptian.-:. The spacious level and unclouded horizon of Chaldea afforded the utmost facilities for observing the celestial phenomena ; and its inhabitants, enjoying the leisure afforded by a pastoral life, and stimulated by the vain desire of obtaining a knowledge of the future from the aspects of the stars, assiduously cultivated astronomy and astrology. By a long series of observations of eclipses, extending, according to the testimony of some authors, over nineteen centuries, or even a longer period, they had discovered the cycle of 223 lunations, or eighteen solar years, which, by bringing back the moon to nearly the same position with respect to her nodes, her perigee, and the sun, brings back the eclipses in the same order. This is supposed to be the period which they distinguished by the name of Saros. They had others, to which they gave the names of Sossos and Neros ; but nothing positive is known with regard to their nature or extent. It is certain, however, that these Chaldaic periods, whatever they were, were purely empiri cal. Detected by the comparison of recorded observations, they imply neither theory nor science, unless, indeed, a simple arithmetical operation is to be considered as such ; nor is there any reason to suppose that the Chaldeans employed any process of computation whatever in their predictions of eclipses. Having once established their cycle they were in possession of a simple means of predict ing all those which occurred in the course of it, with as great a degree of accuracy as they considered requisite.
the Chaldeans in the cultivation of astronomy ; and although they have left behind them still fewer monuments of their labours, they have obtained, through the exaggerated state ments of the Greeks, even a greater reputation. The Greeks acknowledge themselves indebted to the Egyptians for their science and civilisation ; but regarding themselves likewise as descendants of that ancient people, they indulged their vain-glory in magnifying the accounts of the antiquity and knowledge of their supposed ancestors. It is not
improbable that some traditional observations of the
