. Elements of theoretical and descriptive astronomy, for the use of colleges and academies. ner the right ascension and the decli-nation of any celestial body can be determined at any time byobservation. If we thus determine the position of the sun fromday to day, and mark the corresponding points upon our celes-tial globe, we shall find that the sun appears to move in a greatcircle of the sphere from west to east, completing one revolutionin this circle in 365d. 6h. 9m. of our ordinary solar interval of time is called the sidereal year. The great circlein which the sun appears
. Elements of theoretical and descriptive astronomy, for the use of colleges and academies. ner the right ascension and the decli-nation of any celestial body can be determined at any time byobservation. If we thus determine the position of the sun fromday to day, and mark the corresponding points upon our celes-tial globe, we shall find that the sun appears to move in a greatcircle of the sphere from west to east, completing one revolutionin this circle in 365d. 6h. 9m. of our ordinary solar interval of time is called the sidereal year. The great circlein which the sun appears to move is called the ecliptic, and thetwo points in which it intersects the celestial equator are calledthe vernal and the autumnal equinox. p Let Fig. 34 be a representation ofthe celestial sphere. EA Q V is the equi-noctial, Pp is the axis of the sphere, andP the north pole. The circle A C VD re- Epresents the ecliptic, V the vernal, andA the autumnal equinox. The sun isat the vernal equinox on the 21st ofMarch. It thence moves eastward andnorthward, and reaches the point C, fi$.8*.. 84 DISTANCE OF THE SUN. where it na« ics greatestnorthern declination, on the 21 stof June,This point is called the northern summer solstice. From thispoint it moves eastward and southward, passes the autumnalequinox A on the 21st of September, and reaches the point D,called the northern winter solstice, on the 21st of December. Itthence moves towards V, which it reaches on the 21st of March. The obliquity of the ecliptic to the equinoctial is the angleCVQ, measured by the arc CQ. This angle or arc is evidentlyequal to the greatest declination, either north or south, whichthe sun attains, and is found by observation to be about 23° 27. 90. Definitions.—The latitude of a celestial body is its angu-lar distance from the plane of the ecliptic, measured on a greatcircle passing through its poles, and called a circle of Fig. 34 the arc Ks is the latitude of the body s. The longi-tude
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