CHARACTERISTICS OF COMETS

Hawera & Normanby Star, Volume LIII, Issue 9418, 17 August 1907, Page 5

CHARACTERISTICS OF COMETS

AN INTERESTING RECORD. Comets have been "* alternately regarded with feelings of terror amd of welcome in the popular mind. The appearance of Bailey's comet in 1456, just as the Turks .had ibecome masters of Constantinople, and threatened am advance into Europe, was regarded by Christendom with superstitious dread, aod to the Aye Maria was added the prayer, "Lord save us from the devil, the Turk, and the Comet." The discoveries made by scientist of tlhe magnitude of the space filled by comets, and their prodigious velocity, together with Ihe admitted impossibility of always" predicting their approach, have produced' fears of another kind. The groundlessness of such ailarms is sufficiently evident from the extreme Improbability of collision of the nucleus with the earth, and the innocuousn&ss of a contract with the extremely attenuated Biu-rounding matter. It is stated by one authority that on many occasions some of the attenuated vapor onust have come within the earth's attraction amd been absorbed in its atmosphere. The general features of a comet are a definite point or tniudeus, a (nebulous light surrounding the nucleus, and a. luminous train preceding or following the .nucleus. Formerly, when the train preceded the nucleus, as in the case when a comet has passed its perihelion and is receding from the sun, it was called* the heaand, .being termed the tail only when seen, .following the nucleus as the sun was approached. The ■distinction has now disappeared. 4 There are twenty fcnown. periodical comets, eleven of which hay© been observed at more than one perehelion passage. The eleven -have* ihe following periods :— Encke's, 3.3 years; Winnecks % 5.6 years; Brorsen's, 5.5 years;. Temple's No. i, 6 years; D'Arrest's, 6.4 years; Bella's, 6.6 years; Fay's, 7.4 years; Tattle's, 13.8 years; Halley's, 7.6 years,; Temple's No. 2, 52 years; Swifts, 5.5 years. The discovery that comets were celestial bodies, extraneous to the earth's atmosphere, was due to Tcyho Brahe, who measured the parallax of the comet of 1557. Newton succeeded in demonstrating that they were guided in their movements by the principle which controlled the planete in tiheir orbits; amd Bailey was the first, by determining the parabolic elements of a number of comets from the recorded observations, to identify the comet of 1682 with one which had been observed in 1607, and the observations T&oarded by • Kepler and Longomontanus, amd also with a comet observed in 1531 by Apian, ait Ingoldstadt, and thus comfidiantly to predict the return at the end of 1758, <xc beginning of 1759, of a comet which would hav,e the same parabolic elements, The parabolic elements axe elements of a paraJbola ■nearly ooineddent witlh the elongated elliptic onbit of the comet. They are. the inclination and' longitude of the node, which determine the plane of the orbit, the longitude of the perehelion or / point of nearest approach to the sun, the perehelion distance or nearness of approach to the sun, the time of perihelion passage, and the direction of motion, whether direct or retrograde. To determine the parabolic elements, three observations of the comet are sufficient; and, by a table of such elements deduced from the recorded observations, it is possible- to ascertain »t once whether any mewly-observed comet is identical with any that lias been previously observed. The observations which are necessary to determine the orbit of the present/ comet have mot been made locally, and theinr making will be a matter of .'time. It is more than probable thai they will be first concluded by and the .results cabled from the leading observatories of the world.