Newcomb, Simon, 1835-1909, Holden, Edward Singleton, 1846-1914, joint author · New York, H. Holt · leaf 45
we should have twenty-tour semi-circles, all diverging from one pole and meeting at the 26 ASTRONOMY. other, as shown in Fig. 11. The circles thus formed arecalled hour circles. Hence the definition : Hour circles on the celestial sphere are circles passingthrough the two poles and therefore… … Fig. 11a.— circles of the sphere. the north pole. Let A be the position of a star.Then PAB is, by definition, part of the hour circle ofthe star A. The angle ZPA is then called the hourangle of the star. Hence the definition : The hour angle of a star is the angle which its hourcircle makes with…
Astronomy
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