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PRECESSION OF THE EQUINOXES
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PRECESSION OF THE EQUINOXES , in See also:astronomy, the See also:term assigned to the progressive See also:motion of the See also:equinox, because it takes See also:place in a direction from See also:east towards See also:west, opposite to that in which See also:planets move, and in which longitudes are measured. The equinox being defined as the point of intersection of the See also:equator and See also:ecliptic, its motion arises from the fact that both of these See also:great circles are in continuous though slow motion. The motion of the ecliptic is due to the See also:action of the planets on the See also:earth, which produces a slow progressive See also:change in the position of the See also:plane of the earth's See also:orbit, and therefore of the ecliptic. This motion takes place See also:round a See also:diameter of the See also:celestial See also:sphere as an See also:axis or nodal See also:line, which intersects the sphere in two points, which are at See also:present in longitudes about 173° and 353°. The direction of the motion around this axis is such that from the limits 353° through o° to 173°, which includes the vernal equinox, the motion is towards the See also:south, while, in the See also:remainder of the circle, it is towards the See also:north. At the present See also:time the See also:rate of the motion is 46.7" per See also:century. In consequence of the smallness of the See also:angle, 7°, which the axis of motion makes with the line of the equinoxes, its effect on the precession is quite small, now amounting to only 0.14" per annum. Owing to its cause this small See also:part of the precession is called " planetary." The motion of the equator is due to the combined action of the See also:sun and See also:moon on the See also:equatorial protuberance of the earth (see ASTRONOMY). Owing to its cause this largest part of the precession is called " luni-See also:solar." Its fundamental See also:law is that the mean celestial See also:pole at each instant (see See also:NUTATION) moves at right angles to the circle joining it to the pole of the ecliptic as that instant. Hence if the pole of the ecliptic were fixed, the celestial pole would revolve around it in a circle at a See also:constant distance equal to the obliquity of the ecliptic. Owing, however, to the slow change in the position of the pole of the ecliptic, the motion is only approximately in a circle, and the obliquity (F. DR.; W. A. L.) See also:Sophocles represents See also:man's See also:life as See also:woven with a " See also:shuttle of See also:adamant " (See also:Antigone, 622-624). Stoicism formulated a See also:doctrine of See also:providence or See also:necessity. See also:Epicurus denies a divine superintendence of human affairs. A powerful See also:influence in Scandinavian See also:religion was exercised by the belief in " the nornir, or Fates, usually thought of as three sisters." In Brahminic thought See also:Karma, the consequences of action, necessitates rebirth in a See also:lower or higher mode of existence, according to See also:guilt or merit. With some modifications this conception is taken over by See also:Buddhism. The See also:Chinese tao, the See also:order of See also:heaven, which should be the order for earth as well, may also be compared. According to See also:Josephus (Antiq. xviii. 1, 3, 4; xiii. 5, 9) the See also:Sadducees denied See also:fate altogether, and placed See also:good and evil wholly in man's choice; the See also:Pharisees, while recognizing man's freedom, laid emphasis on fate; the See also:Essenes insisted on an See also:absolute 'fate. This statement is exposed to the suspicion of attempting to assimilate the Jewish sects to the See also:Greek See also:schools. In See also:Islam the orthodox See also:theology teaches an absolute See also:predestination, and yet some teachers hold men responsible for the moral See also:character of their acts. The freethinking school of the Mo'tazilites insisted that the righteousness of See also:God in rewarding or punishing men for their actions could be vindicated only by the recognition of human freedom. varies slowly from century to century. At the present time the rate of motion measured on a great circle is about 20" per See also:year; that is to say both the pole and the plane of the equator move through this angle annually. But when measured around the pole of the ecliptic as a centre the motion is about 2.5 times this or, at present, 5o•37" annually. This is the pre, ent amount of the luni-solar precession which, if it remained constant, would carry the pole completely round in a See also:period of 25,730 years. But the exact period varies slightly, owing to the motion of the pole of the ecliptic. The combined effect of the luni-solar and planetary precession or the See also:total motion of the equinox is called the See also:general precession. Its See also:annual amount during our time is 50.2564+0.02220" T, T being the time reckoned from 1900 in centuries. Additional information and CommentsThere are no comments yet for this article.
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