File:Astronomy for high schools and colleges (1881) (14577161480).jpg

Identifier: astronomyforhigh00newc (find matches)
Title: Astronomy for high schools and colleges
Year: 1881 (1880s)
Authors: Newcomb, Simon, 1835-1909 Holden, Edward Singleton, 1846-1914, joint author
Subjects: Astronomy
Publisher: New York, H. Holt and Company
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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in Europe, while on the correspondingnight of the year following it was again seen in this coun-try, and, in fact, was repeated for two or three years, grad-ually dying away. The occurrence of a shower of meteors evidently showsthat the earth encounters a swarm of meteoroids. Therecurrence at the same time of the year, when the earthis in the same point of its orbit, shows that the earthmeets the swarm at the same point in successive years.All the meteoroids of the swarm must of course be movingin the same direction, else they would soon be widely scat-tered. This motion is connected with the radiant jpoi7it,a well-marked feature of a meteoric shower. 382 A8TR0N0MT. Kadiant Point.—Suppose that, during a meteoric shower, wemark the path of each meteor on a star map, as in the figure. If wecontinue the paths backward in a straight line, we shall find thatthey all meet near one and the same point of the celestial sphere—that is, they move as if they all radiated from this point. The
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Fig. 100.—RADiAjfT point of meteoric shower. latter is, therefore, called the radiant point. In the figure the linesdo not all pass accurately through the same point. This is owingto the unavoidable errors made in marking out the path. It is found that the radiant point is always in the same positionamong the stars, wherever the observer may be situated, and that METEORS AND COMETS. 383 it does not partake of the diurnal motion of the earth—that is, asthe stars apparently move toward the west, the radiant point moveswith them. The radiant point is due to the fact that the meteoroids whichstrike the earth during a shower are all moving in the same direc-tion. If we suppose the earth to be at rest, and the actual motionof the meteoroids to be compounded with an imaginary motionequal and opposite to that of the earth, the motion of these imag-inary bodies will be the same as the actual relative motion of themeteoroids seen from the earth. These relative motions will all beparallel ;

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