spaces in equal times. 3. That the squares of the times of the revolutions of the planets are as the cubes of their mean distances from the sun. Galileo, who died in 1642, advanced the science by his observations and by the new revelations he made through his telescopes, which established the truth of the Copernican theory. Newton, born in 1642, carried physical astronomy suddenly to comparative perfection. Accepting Kepler's laws as a statement of the facts of planetary motion, he deduced from them his theory of gravitation. The science was enriched towards the close of the eighteenth century by the discovery by Herschel of the planet Uranus and its satellites, the resolution of the Milky Way into myriads of stars, and the investigation of nebulæ and of double and triple stars. The splendid analytical researches of Lalande, Lagrange, Delambre, and Laplace mark the same period. The nineteenth century opened with the discovery of the first four minor planets; and the existence of another planet (Neptune), more distant from the sun than Uranus, was, in 1845, independently predicted by Leverrier and Adams. Of late years the sun has attracted a number of observers, the spectroscope and photography having been especially fruitful in this field of investigation. By various methods the sun's mean distance has been ascertained within very small limits of error, and found to be nearly 93,000,000 miles. Many additions have been made to the known secondary planets or satellites, including some with retrograde motions. A vast number of asteroids has been discovered, and the width of the zone occupied by them found to be much more extensive. Much success has been achieved in ascertaining the parallax of fixed stars.
The objects with which astronomy has chiefly to deal are the earth, the sun, the moon, the planets, the fixed stars, comets, nebulæ, and meteors. The stellar universe is composed of an unknown host of stars, many millions in number. Those visible to the naked eye were in ancient times grouped into the constellations still recognized. The nebulæ are cloud-like patches of light scattered all over the heavens. Some of them have been resolved into star-clusters, but many of them are masses of incandescent gas. Of the so-called fixed stars, many form binary or multiple systems, the members revolving in orbits under each other's attractions, while other more scattered groups are moving clusters, travelling in parallel paths through space like flocks of birds. Variable stars and extinct or dark stars are also known. The fixed stars preserve, at least to unaided vision, an unalterable relation to each other, because of their vast distance from the earth. Their apparent movement from east to west is the result of the earth's revolution on its axis in twenty-four hours from west to east. The planets have not only an apparent, but also a real and proper motion, since, like our earth, they revolve around the sun in their several orbits and periods. The nearest of these bodies to the sun is Mercury. Venus, the second planet from the sun, is to us the brightest and most beautiful of all the planets. The Earth is the first planet accompanied by a satellite or moon. Mars, the next planet, has two satellites, discovered in 1877. Its surface has a variegated character, and the existence of land, water, snow, and ice has been inferred. The Asteroids, of which over 1000 are known, form a broad zone of small bodies, at distances from a little beyond the earth's to that of Jupiter. Jupiter, the largest planet, has at least nine satellites, of which the two outermost have retrograde motion. Its surface is diversified by spots, markings, and bands parallel to its equator. Saturn, with its nine or more satellites and broad thin rings in its equatorial plane, is, perhaps, the most striking telescopic object in the heavens. Urănus—discovered by Herschel in 1781—is accompanied by four satellites. Neptune, the farthest removed from the sun, has one satellite, the motion of which is retrograde. Besides the planets, quite a number of comets are known to be members of the solar system. The physical constitution of these bodies is still one of the enigmas of astronomy. The observation of meteors has recently attracted much attention. They are seen in largest numbers in the autumn months. Meteor streams are supposed to represent the results of the disintegration of comets. Among the more modern astronomers we may mention: Gustav Kirchhoff, G. B. Donati, Christian Doppler, H. C. Vogel, Sir William Huggins, Simon Newcomb, and Sir David Gill. See Earth, Sun, Moon, Planet, Comet, Stars, Asteroids, Celestial Photography, Spectrography, &c.—BIBLIOGRAPHY: Sir J. N. Lockyer, Dawn of Astronomy; Sir G. C. Lewis, Historical Survey of the Astronomy of the Ancients; Sir. F. W. Dyson, Astronomy; Sir R. Ball, Atlas, and Popular Guide to the Heavens; G. P. Serviss, Astronomy with an Opera-glass; The Pleasures of the Telescope; A. M. Clerke, History of Astronomy during the 19th Century, H. Macpherson, Romance of Modern Astronomy; C. A. Young, General Astronomy; G. F. Chambers, Handbook of Astronomy (3 vols.); E. W. Maunder, Astronomy of the Bible; A. C. D. Crommelin, The Star World; Agnes Giberne, Sun, Moon, and Stars (popular).
Astropalia, an island in the Ægean Sea. It was occupied during the Balkan war of 1912 by the Italians under Admiral Presbitero and General d'Ameglio.
Astrophysics. See Spectroscopy.
Astur. See Goshawk.
Astu´ria, or The Asturias, a Spanish principality, now forming the province of Oviedo, on the north coast of Spain; an alpine region, with steep and jagged mountain ridges, valuable minerals, luxuriant grazing lands, and fertile well-watered valleys. The heir apparent of Spain has borne since 1388 the title of Prince of the Asturias. See Spain.
Asty´ages (-jēz), last king of the Medes, 593-558 B.C., deposed by Cyrus, an event which transferred the supremacy from the Medes to the Persians.
Asuncion (a˙-su¨n-thē-on´), or Nuestra Señora de la Asuncion (Eng. Assumption), the chief city of Paraguay, on the River Paraguay, picturesquely situated and with good public buildings. It was founded in 1537 on the feast of the Assumption. Its trade is mostly in the yerba tea, hides, tobacco, oranges, &c. It was taken and plundered by the Brazilians in 1869. A railway runs for a short distance into the interior. Pop. (1920), 99,836.
