File:Lectures on astronomical theories (1876) (14783364045).jpg

Identifier: lecturesonastron14harr (find matches)
Title: Lectures on astronomical theories
Year: 1876 (1870s)
Authors: Harris, John
Subjects: Astronomy
Publisher: Montreal, Lovell Printing and Publishing Co.
Contributing Library: University of California Libraries
Digitizing Sponsor: Internet Archive

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the time of an observed appearance until the next. Theorbit, as shown by the figure, is compound, belonging inpart to the planet Jupiter. It is evident that if weassume these relative periods for the comet and tlie earth,that the earth will make two complete revolutions andbe in advance of the comet by about 73^ days in the 1stperiod ; in the 2nd period, the earth will make twocomplete revolutions and gain another 73 J days, makingtogether 146; days, and at the end of the third period,the earth will have made six annual revolutions and havegained 220 days. At this time the comet again becomesvisible from the earth in a situation nearly the samerelatively to the earth as when it was observed 2410days previously. During this longer term the cometmight be twice visible from the earth ; but the frequencyof the comets re-appearance would be, in the first place,dependant upon the relative situation in its orbit of theplanet Jupiter, because if the comet was in its planetary Orbit of Jupiter
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5tiOi o •^^/idnf fo ^O 1^ ^^ o 5; ^ 3ix ORBIT OF BIELAs COMET. 35 orbit (revolving around Jupiter) at the time that theearth passed by, the comet would not be visible from theearth until overtaken again in the next revolution; and,in the second place, it should be observed that, when thecomet becomes visible in November or February, theearth is situated (vertically) much below the plane ofthe ecliptic, not very far from its point of maximumdepression j now, if the comet was seen at that time ofthe year when the earth is near its point of maximumelevation and therefore much above the plane of theccHptic, the difference in the apparent relative situationmight alone prevent the recognition of the comet. *According to this explanation the comets true periodconsidered as its third return to the same sidereal (orfixed) place in the heavens (i.e., to a place situated at thesame point of the solar compass) will be somewhat(about 145 daj^s) more than 7 years, because when thecomet again beco

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