The elements of astronomy; a textbook . avens at the celestial pole; and the planeof the earths equator, which keeps parallel to itself duringher annual circuit around the sun, marks out only one celestialequator in the sky. 9. Place of a Heavenly Body. — This is simply the pointwhere a line, drawn from the observer through the body inquestion and continued onward, pierces the sphere. It de-pends solely upon the directionof the body, and is obviouslyin no way affected by its dis-tance. Thus in Fig. 1, A, B, C,etc., are the apparent places ofa, 6, c, the observer being at that are nea
The elements of astronomy; a textbook . avens at the celestial pole; and the planeof the earths equator, which keeps parallel to itself duringher annual circuit around the sun, marks out only one celestialequator in the sky. 9. Place of a Heavenly Body. — This is simply the pointwhere a line, drawn from the observer through the body inquestion and continued onward, pierces the sphere. It de-pends solely upon the directionof the body, and is obviouslyin no way affected by its dis-tance. Thus in Fig. 1, A, B, C,etc., are the apparent places ofa, 6, c, the observer being at that are nearly in linewith each other, as h, i, 7c, willappear close together in the sky,however great their real dis-tance from each other may moon, for instance, oftenlooks to us very near a star, which is really of course at an immeasurable distance beyondher. 10. Angular Measurement.—It is clear that we cannot prop-erly measure the apparent distance of two heavenly bodiesfrom each other in the sky by feet or inches. To say that two. Fig. 1. § 10] ANGULAR MEASUREMENT. 7 stars are about five feet apart, for instance (and it is not veryuncommon to hear such, an expression), means nothing unlessyou tell how far from the eye the five-foot measure is to beheld. If 20 feet away, it means one thing, and corresponds,nearly, to the apparent length of the Dipper-handle in thesky (see Art. 23) ; if 100 feet away, it corresponds to anapparent distance only about one-fifth as great, or to one ofthe shorter sides of the Dipper-bowl (see Art. 23) ; but ifthe five-foot measure were a mile away, its length would cor-respond to an apparent distance about one-tenth the apparentdiameter of the moon. The proper units for expressing appar-ent distances in the sky are those of angle, viz.: radians, or elsedegrees (°), minutes (), and seconds (). The Great Bearstail or Dipper-handle is about 16 degrees long, the long side ofthe Dipper-bowl is about 10 degrees, the shorter sides are 4° or5°; the
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