Elements of astronomy ..with explanatory notes, and questions for examination . s,in Fig. 18, EQ is the equator, and l^Q1 the celestial What is meant by celestial meridians? Explain from figure. What are the rela-tive positions of the plane of the meridian of any place and the plane of its horizon 1What is the meaning of the term meridian? What is the terrestrial equator? Whatthe celestial ? VERTICAL CIRCLES. 49 equator. They appear as straight lines in the figure,because we see them in the direction of their planes. 65. Vertical Circles. Vertical circles are thosewhich are imagined to be form
Elements of astronomy ..with explanatory notes, and questions for examination . s,in Fig. 18, EQ is the equator, and l^Q1 the celestial What is meant by celestial meridians? Explain from figure. What are the rela-tive positions of the plane of the meridian of any place and the plane of its horizon 1What is the meaning of the term meridian? What is the terrestrial equator? Whatthe celestial ? VERTICAL CIRCLES. 49 equator. They appear as straight lines in the figure,because we see them in the direction of their planes. 65. Vertical Circles. Vertical circles are thosewhich are imagined to be formed by planes passingthrough the zenith, perpendicular to the horizon, andintersecting the celestial sphere. The vertical circlepassing through the east and west points of the horizonis termed the prime vertical, while that which intersectsthe north and south points becomes a meridian. Thus,in Fig. 19, where A represents the earth, SZWMN thecelestial sphere, Z the zenith, and the plane SW1STE thehorizon—PZHM is a vertical circle, WZEM the primevertical, and SZNM a AZIMUTH AND ALTITUDE OF A STAR. 66. The Position of a Star—how place of a star in the sky may be determined inthree ways. First, by referring it to the planes of acelestial meridian and of the horizon. Secondly, bynoting its distance from the planes of a given meridian What are vertical circles ? What the prime vertical 1 Is a meridian a vertical circle 1Explain from figure. In how many ways is the position of a star fixed? Describe them 5 50 THE EARTH VIEWED ASTRONOMICALLY. and the celestial equator. Thirdly, by referring it to theplanes of a given meridian and the 67. Azimuth, Amplitude, Altitude, and Zenith-distance. Proceeding according to the first method,we should ascertain the situation of a star in the follow-ing way. Suppose the star is the beautiful luminary,Alpha Lyrae, and that we observe it in the east. Hav-ing previously found the plane of the meridian, bymethods h
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