Elements of astronomy ..with explanatory notes, and questions for examination . resents the paththat the pole of the equator, Pl would describe aroundthe pole of the ecliptic, P, if precession alone existed; andA, is the small ellipse which P1 would describe if nutation Lunar. Within what period of time do the solnr variations occur? Within whatthe lunar? What kind of figure does the pole of the equator describe in consequenceof nutation ? What is the extent of this ellipse ? Where does its centre lie ? illustratethis subject by figures 33 and 34. NUTATION. 103 occurred without precession. Now
Elements of astronomy ..with explanatory notes, and questions for examination . resents the paththat the pole of the equator, Pl would describe aroundthe pole of the ecliptic, P, if precession alone existed; andA, is the small ellipse which P1 would describe if nutation Lunar. Within what period of time do the solnr variations occur? Within whatthe lunar? What kind of figure does the pole of the equator describe in consequenceof nutation ? What is the extent of this ellipse ? Where does its centre lie ? illustratethis subject by figures 33 and 34. NUTATION. 103 occurred without precession. Now, since these motionsco-exist, it is evident that neither a perfect circle nor acomplete ellipse will be described by the pole, P1; butat one time it will be outside the circumference, B, andat another within, revolving about P all the while. Itwill, therefore, actually describe a circular waving path,like that exhibited in Fig. 34, where P is the pole of theecliptic, and the pole of the equator advances towardsP and recedes from it, as it follows the path, AA^BB*,and so NUTATION. 171. The influence of the moon in producing nuta-tion is to that of the sun, as five to seven. 172. Obliquity of the Ecliptic Affected by Nu-tation. It is evident from an inspection of the abovefigure that the pole of the equator approaches to and re-cedes from the pole of the ecliptic at determinate in-tervals of time. The inclination of the plane of theequator to that of the ecliptic, must, therefore, fluctuatein the same manner, since the axes of the equator andecliptic are always at right angles to their respectiveplanes. Eecorded observations prove this point; a feware here given: What is the ratio of the moons influence to the suns in producing nutation 1 Is theobliquity of the ecliptic effected by nutation 1 Why 1 Do recorded observations show achange in the obliquity. Prove this from the table given. 104 THE EARTH VIEWED ASTRONOMICALLY. Date. Observers. Obliquity. 1100 Tcheou-kong, (
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