Astronomy for amateurs . as round some altar of the gods, he grantsthem liberty to visit other heavens, to seek fresh uni-verses. . The original parabola is converted into an ellipse,if the imprudent adventurer in returning to the Sunpasses near some great planet, such as Jupiter, Saturn,Uranus, or Neptune, and suffers its attraction. It isthen imprisoned by our system, and can no longer es-cape from it. After reenforcement at the solar focus,it must return to the identical point at which it felt thefirst pangs of a new destiny. Henceforward, it belongsto our celestial family, and circles in a
Astronomy for amateurs . as round some altar of the gods, he grantsthem liberty to visit other heavens, to seek fresh uni-verses. . The original parabola is converted into an ellipse,if the imprudent adventurer in returning to the Sunpasses near some great planet, such as Jupiter, Saturn,Uranus, or Neptune, and suffers its attraction. It isthen imprisoned by our system, and can no longer es-cape from it. After reenforcement at the solar focus,it must return to the identical point at which it felt thefirst pangs of a new destiny. Henceforward, it belongsto our celestial family, and circles in a closed curve. 184 THE COMETS otherwise, it is free to continue its rapid course towardother suns and other systems. As a rule, the telescope shows three distinct parts ina comet. There is first the more brilliant central point,or nucleus, surrounded by a nebulosity called the hair,or brush, and prolonged in a luminous appendix stretch-ing out into the tail. The head of the comet is the brushand the nucleus Fig. 53.—The tails of Comets are opposed to the Sun. It is usually supposed that the tail of a comet followsit throughout the course of its peregrinations. Nothingof the kind. The appendix may even precede thenucleus; it is always opposite the Sun,—that is to say, itis situated on the prolongation of a straight line, startingfrom the Sun, and passing through the nucleus (Fig. 53).The tail does not exist, so long as the comet is at adistance from the orb of day; but in approaching theSun, the nebulosity is heated and dilates, giving birth 185 ASTRONOMY FOR AMATEURS to those mysterious tails and fantastic streamers whosedimensions vary considerably for each comet. Thedilations and transformations undergone by the tailsuggest that they may be due to a repulsive force emana-ting from the Sun, an electric charge transmitted doubt-less through the ether. It is as though Phoebus blewupon them with unprecedented force. Telescopic comets are usually devoid of tail, eve
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