A primary astronomy .. . ariation in her elongations indicate? That she revolves in an elliptical orbit. [1. It will be obvious, without illustration, that if she is further from the Sun atone time than at another (as is evident from the difference in her elongations), she can-not revolve in a circle, and her orbit must be elliptical. 2. The eccentricity of her orbit is ascertained by observing the difference betweenher greatest and least distance, which is only about 3°. Her orbit, therefore^ is verynearly a circle.] 248. When is Venus Morning Star ? When she is west of the Sun, and rises bef
A primary astronomy .. . ariation in her elongations indicate? That she revolves in an elliptical orbit. [1. It will be obvious, without illustration, that if she is further from the Sun atone time than at another (as is evident from the difference in her elongations), she can-not revolve in a circle, and her orbit must be elliptical. 2. The eccentricity of her orbit is ascertained by observing the difference betweenher greatest and least distance, which is only about 3°. Her orbit, therefore^ is verynearly a circle.] 248. When is Venus Morning Star ? When she is west of the Sun, and rises before him. [She must be west of the Sun, of course, from her inferior to her superior conjunc-tion. See cut, page 50.] 249. When is she Evening Star? When she is east of the Sun, and remains above thehorizon after he has gone down. [From her superior to her inferior conjunction she is east of the Sun, and Morning Star.] PRIMARY ASTRONOMY. 55 VENDS AS MORNING AND EVENING ???\\l/j- J-: #^i-.^sr ;F. [Let the student hold the book up south of him, and he will at once see why Venusis alternately Morning and Evening Star. Let the plane A B represent the sensible orvisible horizon, C D the apparent daily path of the Sun through the heavens, and Ethe Earth in her apparent position. The Sun is shown at three different points;namely, rising in the east; on the meridian; and setting in the west: while Venus isseen revolving around him from west to east, or in the direction of the arrows. Nowit is obvious that when Venus is at F, or west of the Sun, she sets before him as at G,and rises before him as at H- She must, therefore, be Morning- Star. On the otherhand, when she is east of the Sun, as at J, she lingers in the west after the Sun hasgone down, as at K, and is consequently Evening- Star. 2. In this cut, Venus would be at her greatest elongation eastward at J, and west-ward at F; and in both cases would be stationary. At L and M she would be inconjunction with the
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectastronomy, bookyear18
