ASTRONOMY (Gr. astron, a star, nomos, a law) teaches whatever is known of the heavenly bodies. A. may be properly divided under three heads. 1. Geometrical or Mathematical A., including the exact determination of the numerical and geometrical ele ments of the heavenly bodies—that is, their distances, shapes, magnitudes, the figures they describe in their motions, etc. 2. Physical A., or the nature of the powers or forces that carry on the heavenly motions, the laws that they observe, and the calculation of the motions from a knowledge of these laws. 3. Sidereal A., or whatever is ascertained regarding the universe of the fixed stars. Practical A. might form another division, which would include a knowledge of the various astronomical instruments; and a famil iarity generally with the rules and calculations by which the requisite results are deduced from observations. • Such parts of this extensive subject as are deemed suited to the present work, will be found under their appropriate heads, such as ABERRATION OF LIGHT, CIRCLE, COMET, EQUATOR, FIXED STARS, LII3RATION, PARALLAX, PLANETOIDS, PLANETS, PRECESSION, REFRACTION, SOLAR SYSTEM, SUN, TIME, TRANSIT INSTRU3IENT, etc. A brief sketch of the history of astronomical discovery is all that can be attempted in the present article.
The history of A. dates from a very early period. It is the most ancient of all the sciences. The Chinese, Hindoos, Chaldeans, even the Greeks, are known to have investigated the heavens very long before the Christian era. But with the first four nations, A. may be said to have been a sentiment rather than a science—a vague notion built up out of crude speculations, rather than a correct theory founded on sys tematic observation. In China, A. was intimately associated with state politics; the Indians, Chaldeans, and Egyptians made it a matter of religion; and each of these nations applied it to astrological purposes. In Greece alone was it prosecuted for its own sake.
The Chinese, Chaldeans, Hindoos, and Egyptians each claim the honor of having been the first students of A., and each has had advocates to support its claim. The Tir valore tables (asserted by the Hindoos to belong to an epoch of 3102 ;years B.C.—the com mencement of the Cali-yug, or iron age, of their mythology—at which period a conjunc tion of the sun, moon, and planets is said to have occurred) are, so far as their date is concerned, altogether unreliable. Modern calculations have conclusively proved that no such conjunction could possibly have taken place at the time specified; and the elements of the tables are, in the general opinion of scientific men, of a character far in advance of the actual observations of that period. There is no doubt that the epoch is fictitious
—that the date of these tables is fixed much earlier than their internal evidence justifies; but it is matter of dispute whether they were the result of the observations of Hindoos themselves at sonic later 'period before the Christian era, or whether they were con structed after that era from data furnished to them by the Arabs or Greeks. Those who hold the former view, quote the well-known mathematical attainments of the Indians, and their aversion to intereonme with foreigners, as arguments in its favor; those who support the latter, point out that the tables are a mean between those of Ptolemy and Albategnius, or Al Batani, a distinguished Arabian astronomer, and therefore likely to have been derived from these two sources. Those who are interested in the question of the originality of these tables, may refer to Delambre, and to Bailly's (list. de l' Astrono mie Indienne.
The Chinese have astronomical annals claiming to go back 2857 years n.c. Iu these there is little record of anything but of the appearance of comets and solar eclipses; and regarding the latter phenomena, they tell nothing, save the fact and date of their occur-. rence. Professional astronomers were compelled to predict every eclipse under pain of death. The popular idea was that an eclipse was a monster evil designs on the sun, and it was customary to make a great noise by shouting, beating of gongs, etc., in order to frighten it away from its solar prey. The many eclipses which the Chinese report have been recalculated, but not more than one anterior to the time of Ptolemy could be veri fied. At an early period, however, the Chinese appear to have been acquainted with the luni-solar cycle of 19 years (introduced into Greece by Meton, and since known as the Metonic cycle), and they had also divided the year into 365+ days. Solstitial observ ances are said to have been made by a gnomon in the 11th c. B.C. To the burning of all scientific books by one of their princes (Tsin-Chi-Hong-Ti), 221 B.C., the Chinese attrib ute the loss of many theories or methods previously in use. The precession of the equi noxes was not known to the Chinese until 400 A.D., but long prior to that they were familiar with the motion of the planets.