Astronomy for the use of schools and academies (1882) (14577674870)

Identifier: astronomyforuseo00gill (find matches)

Title: Astronomy for the use of schools and academies

Year: 1882 (1880s)

Authors: Gillet, J. A. (Joseph Anthony), 1837-1908 Rolfe, W. J. (William James), 1827-1910

Subjects: Astronomy

Publisher: New York : Potter, Ainsworth, & Co.

Contributing Library: The Library of Congress

Digitizing Sponsor: The Library of Congress

Text Appearing Before Image:

k on a celestial globe theapparent paths of the meteors which fall during a shower,or if we trace them back on the celestial sphere, we shallfind that they all meet in the same point, as shown in Fig.352. This point is called the radiant point. It alwaysappears in the same position, wherever the observer is situ-ated, and does not partake of the diurnal motion of theearth. As the stars move towards the west, the radiantpoint moves with them. The point in question is purelyan effect of perspective, being the vanishing point ofthe parallel lines in which the meteors are actually moving. ASTRONOMY. 3II These lines are seen, not in their real direction in space,but as projected on the celestial sphere. If we look up-wards, and watch snow falling through a calm atmosphere,the flakes which fall directly towards us do not seem tomove at all, while the surrounding flakes seem to divergefrom them on all sides. So, in a meteoric shower, ameteor coming directly towards the observer does not seem

Text Appearing After Image:

Fig. 352. to move at all, and marks the point from which all theothers seem to radiate. 312. The August Meteors.—A meteoric shower of nogreat brilliancy occurs annually about the 10th of August.The radiant point of this shower is in the constellation Per-seus, and hence these meteors are often called the Perseids.The orbit of these meteoroids has been pretty accuratelydetermined, and is shown in Fig. 353. 312 ASTRONOMY. It will be seen that the perihelion point of this orbit isat about the distance of the earth from the sun ; so that the earth encounters the mete-ors once a year, and this takesplace in the month of August.The orbit is a very eccentricellipse, reaching far beyondNeptune. As the meteoric dis-play is about equally brilliantevery year, it seems probablethat the meteoroids form astream quite uniformly dis-tributed throughout the wholeorbit. It probably takes oneof the meteoroids about a hun-dred and twenty-four years topass around this orbit. 313. Th e Nov em be? Meteors

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1882

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