Page:The American Cyclopædia (1879) Volume XVI.djvu/323

 VENUS 303 her, but usually the offerings consisted of in- cense and garlands of flowers. Festivals were celebrated in her honor, the principal of which were called Aphrodisia. Modern scholars re- gard Aphrodite as originally identical with the Phoenician Astarte (in the Bible Ashtoreth), or with Baaltis (by some identified with the Ashe- rah of the Bible), and think that her worship was introduced at a very early period by the Phcenicians into Cyprus and Cythera, whence it spread over Greece, and in the course of its development became wholly Grecian. Venus was a favorite subject of ancient sculpture. The statues known as the Venus de' Medici and the Venus of Milo are among the most cele- brated works that have been preserved from antiquity. The former, exhumed in the 17th century in 11 pieces, is in Florence; the latter, found in the island of Milo in 1820, is in the Louvre, in Paris. VENUS, the second planet in order of distance from the sun. According to the estimate of the sun's distance used throughout this work (91,430,000 m.), Venus travels at a mean dis- tance from the sun of about 66,134,000 m. The eccentricity of her orbit is small, not exceeding 0-00686, so that her greatest distance, 66,586,- 000 m., does not exceed her least distance, 65,- 682,000 m., by more than about 900,000 m. In estimating her greatest and least distances from the earth, accordingly, it is more impor- tant to notice the effect of the earth's variation of distance, which amounts (see EAKTH) to about 3,000,000 m. The actual point of near- est approach between the two orbits lies in longitude about 70, and here the orbits are about 24,150,000 m. apart; this then is the nearest approach Venus can ever make to the earth. The orbits are furthest apart in about longitude 250, where they are separated by about 26,500,000 m. ; and adding to this the diameter of Venus's orbit, about 132,300,000 m., we find the greatest distance separating the two planets to be about 158,800,000 m. The mean inclination of Venus's orbit to the eclip- tic is about 3 23' 31"; but her path is not so largely inclined to the mean plane of the solar system. Her mean sidereal revolution is com- pleted in 224-700787 days, and her mean syno- dical revolution in 583-920 days. Her diameter is about 7,510 m. ; her volume 855 thousandths of the earth's, her mass about 885 thousandths (her density exceeding the earth's in the pro- portion of 103 to 100). Venus, travelling on a path within the earth's, is never seen in op- position, passing between the earth and sun when at her nearest. At this time she is of course invisible, her dark hemisphere being 'turned toward the earth. On the other hand, when she turns her fully illuminated hemi- sphere toward the earth, she is not only at her furthest, but lies almost directly on the prolon- gation of a line directed toward the sun, and is therefore lost in his superior lustre. Between these phases she exhibits all the figures shown by the moon, passing from a nearly full disk 816 VOL. xvi. 20 to the finest crescent (as an evening star), and from finest crescent, after her disappearance in inferior conjunction, to nearly a full disk (as a morning star), when she again disappears in superior conjunction. But as her distance from the earth, unlike the moon's, undergoes great variations, she varies in apparent size as well as in phase, having the least diameter when nearest to a full orb, and the greatest when her crescent of light is finest. She lies furthest from the sun in the heavens when her disk is about half illuminated, the distance (her elon- gation, as it is called) varying in different By- nodical revolutions from about 45 to about 47 12'. Although this planet approaches the earth so much more closely than her rival in beauty, Jupiter, it has not been found possible to ex- amine her surface with the telescope to any very useful purpose. Her great brightness in- troduces a difficulty which does not exist in the case of Jupiter, closely though he resembles her in appearance when both are seen under like conditions with the unaided eye ; for the illumination of Venus exceeds that of Jupiter (mile for mile of surface) fully 48 times, though the intrinsic brilliancy of Venus does not surpass Jupiter's much more than 20 times. It is singular that, notwithstanding this diffi- culty, the first observers with the telescope achieved considerable success in recognizing and watching spots on her surface. In fact, the best telescopes of modern times fail to show spots which Cassini, Bianchini, and others of the early observers agree in describing. If the earlier observers had deduced different rotation periods, we should be led to conclude that the spots they saw had no real existence ; and this indeed has been the general conclusion to which modern astronomers have been led. Yet it should be noted that in presence of the close agreement between the rotation periods deduced by Cassini, Schroter, and De Vico, it is difficult to reject altogether the evidence which led to such closely accordant results. Domenico Cassini, after long seeking in vain for recognizable marks, noted in 1667 a bright spot not very far from the southern horn of the planet ; and from observations of this spot he deduced a rotation period of about 23 hours. In 1726 Bianchini made observations whence he deduced the monstrous period of 24 days 8 hours. (It was on this rotation period that Ferguson based his remarkable account of the diurnal phenomena of Venus.) The younger Cassini, having carefully compared his father's observations with Bianchini's, found that both series could be explained by a rotation period of 23 hours and between 21 and 22 minutes, whereas a period of 24 days 8 hours could not be reconciled with D. Cassini's observa- tions. This explanation was received, because it was known that Bianchini's observations were not continuous, but interrupted for want of sky room, a neighboring building inter- fering with his view of the planet. Schroter's observations led to the rotation period 23 h.