Astralite. See Explosives.
Astral Spirits, spirits formerly believed to people the heavenly bodies or the aerial regions. In the Middle Ages they were variously conceived as fallen angels, souls of departed men, or spirits originating in fire, and belonging neither to heaven, earth, nor hell. Paracelsus regarded them as demoniacal in character.
Astrin´gent, a medicine which contracts the organic textures and canals of the body, thereby checking or diminishing excessive discharges. The chief astringents are the mineral acids, alum, lime-water, chalk, salts of copper, zinc, iron, lead, silver; and among vegetables catechu, kino, oak-bark, and galls.
Astroca´ryum, a genus of tropical American palms, species of which yield oil and valuable fibre. Tucum oil and tucum thread are obtained from A. vulgāre.
As´trolabe, an instrument formerly used for taking the altitude of the sun or stars, now superseded by the quadrant and sextant. The name was also formerly given to an armillary sphere.—Cf. Chaucer, Treatise on the Astrolabe.
Astrolabe Bay, an inlet on the N.E. coast of Australian New Guinea.
Astrol´ogy, literally, the science or doctrine of the stars. The name was formerly used as equivalent to astronomy, but is now restricted in meaning to the pseudo-science which pretends to enable men to judge of the effects and influences of the heavenly bodies on human and other mundane affairs, and to foretell future events by their situations and conjunctions. As usually practised, the whole heavens, visible and invisible, were divided by great circles into twelve equal parts, called houses. As the circles were supposed to remain immovable, every heavenly body passed through each of the twelve houses every twenty-four hours. The portion of the zodiac contained in each house was the part to which chief attention was paid, and the position of any planet was settled by its distance from the boundary circle of the house, measured on the ecliptic. The houses had different names and different powers, the first being called the house of life, the second the house of riches, the third of brethren, the sixth of marriage, the eighth of death, and so on. The part of the heavens about to rise was called the ascendant, the planet within the house of the ascendant being lord of the ascendant. The different aspects of the planets were of great importance. To cast a person's nativity (or draw his horoscope) was to find the position of the heavens at the instant of his birth, which being done, the astrologer, who knew the various powers and influences possessed by the sun, the moon, and the planets, could predict what the course and termination of that person's life would be. The temperament of the individual was ascribed to the planet under which he was born, as saturnine from Saturn, jovial from Jupiter, mercurial from Mercury, &c., words which are now used with little thought of their original meaning. The virtues of herbs, gems, and medicines were supposed to be due to their ruling planets. The history of astrology, which was the foster-sister of astronomy, goes back to the early days of the human race. Egyptians and Hindus, as well as the nations on the Euphrates and Tigris, were zealous astrologers. The Christian Church strongly opposed the teachings of astrology, but its study spread among Jews and Arabs during the Middle Ages. Francis Bacon abused the astrologers of his day, and Swift wrote against them his famous Prediction for the Year 1708, by Isaac Bickerstaff, Esq.—BIBLIOGRAPHY: E. H. Bennet, Astrology; G. Wilde, Chaldean Astrology Up-to-date; A. Maury, La Magie et l'astrologie à l'antiquité et au moyen âge; A. J. Pearce, Textbook of Astrology.
Astron´omy (from Gr. astron, a heavenly body, and nemein, to classify or arrange) is that science which investigates the motions, distances, magnitudes, and various phenomena of the heavenly bodies. The science may be divided into several branches. Descriptive astronomy denotes merely a presentation of astronomical facts in a systematic but popular form; practical astronomy treats of the instruments used in observing the celestial bodies, the methods
of their employment, and the manner of deducing results from the observations; investigation of the causes of the motions of these bodies was formerly termed physical astronomy, but now generally dynamical or gravitational astronomy; physical astronomy or astro-physics is the comparatively modern branch which deals with their physical conditions, radiation, temperature, and chemical constitution. Recent years have added two new fields of investigation which are full of promise for the advancement of astronomical science. The first of these—celestial photography—has furnished us with invaluable light-pictures of the sun, moon, and other bodies, and has recorded the existence of myriads of stars invisible even to the best telescopes; while the second, spectrum analysis, now employed by many scientists, reveals to us a knowledge of the physical constituents of the universe, telling us for instance that in the sun (or his atmosphere) there exist many of the elements familiar to us on the earth. It is also applied to the determination of the velocities with which stars are approaching, or receding from, our system; and to the measurement of movements taking place within the solar atmospheric envelopes. From analysis of some of the unresolved nebulæ the inference is drawn that they are not star-swarms but simply incandescent gas; whence a second inference results favourable to the hypothesis of the gradual condensation of nebulæ, and the successive evolutions of suns and systems.
The most remote period to which we can go back in tracing the history of astronomy refers us to a time about 2500 B.C., when the Chinese are said to have recorded the simultaneous conjunction of Saturn, Jupiter, Mars, Mercury, and the moon. This remarkable phenomenon is found, by calculating backward, to have taken place 2460 B.C. Astronomy has also an undoubtedly high antiquity in India. The mean annual motion of Jupiter and Saturn was observed as early as 3062 years B.C.; tables of the sun, moon, and planets were formed, and eclipses calculated. In the time of Alexander the Great, the Chaldeans or Babylonians had carried on astronomical observations for 1900 years. They regarded comets as bodies travelling in extended orbits, and predicted their return; and there is reason to believe that they had correct ideas regarding the solar system. The priests of Egypt gave astronomy a religious character; but their knowledge of the science is testified to only by their ancient zodiacs and the position of their pyramids with relation to the cardinal points. It was among the Greeks that astronomy took a more scientific form. Thales of Miletus (born 639 B.C.) predicted a solar eclipse, and his successors held opinions which are in many respects wonderfully in accordance with modern ideas. Pythagoras (500 B.C.) and his followers formed theories of the planetary system. They taught the sphericity and revolution of the earth, but placed an imaginary 'Central Fire', not the sun itself, at the centre of the system. Great progress was made in astronomy under the Ptolemies, and we find Timochares and Aristyllus employed about 300 B.C. in making useful planetary observations. But Aristarchus of Samos (born 267 B.C.) is said, on the authority of Archimedes, to have far surpassed them, by teaching the double motion of the earth around its axis and around the sun. A hundred years later Hipparchus determined more exactly the length of the solar year, and the eccentricity of the ecliptic, discovered the precession of the equinoxes, and even undertook a catalogue of the stars. It was in the second century after Christ that Claudius Ptolemy, a famous mathematician of Pelusium in Egypt, propounded the system that bears his name, viz., that the earth was the centre of the universe, and that the sun, moon, and planets revolved around it in the following order: nearest to the earth was the sphere of the moon; then followed the spheres of Mercury, Venus, the Sun, Mars, Jupiter, and Saturn; then came the sphere of the fixed stars; these were succeeded by two crystalline spheres and an outer sphere named the primum mobile or first movable, which last was again circumscribed by the cœlum empyreum, of a cubic shape, wherein happy souls found their abode. The Arabs began to make scientific astronomical observations about the middle of the eighth century, and for 400 years they prosecuted the science with assiduity. Ibn-Yunis (A.D. 1000) made important observations of the perturbations and eccentricities of Jupiter and Saturn. In the sixteenth century Nicolaus Copernicus, born in 1473, introduced the system that bears his name, and which recognized the sun's central place in the solar system, and that all the other bodies, the earth included, revolve around it. This arrangement of the universe (see Copernicus) came at length to be generally received on account of the simplicity it substituted for the complexities and difficulties of the theory of Ptolemy. The observations and calculations of Tycho Brahe, a Danish astronomer, born in 1546, continued over many years, were of the highest value, and secured for him the title of regenerator of practical astronomy. His assistant and pupil, Kepler, born in 1571, was enabled, principally from the data provided by his master's labours, to arrive at those laws which have made his name famous: 1. That the planets move, not in circular, but in elliptical orbits, of which the sun occupies a focus. 2. That the radius vector, or imaginary straight line joining the sun and any planet, moves over equal