Newcomb, Simon, 1835-1909, Holden, Edward Singleton, 1846-1914, joint author · New York, H. Holt and Company · leaf 32
er being cut off by the earth. We may also imagine a plane passing through the cen-tre of the earth, parallel to the horizon of the observer.This plane will intersect the celestial sphere in a circlebelow that of the observers horizon by an amount equalto the radius of the earth. This circle is… … The Visible Hemisphere.—5 X, thehorizon ; Z, the zenith : *S. any star ;S Hy its altitude ; U X, its azimath. point in comparison, the rational and sensible horizons areconsidered to coincide on the celestial sphere. The vertical line. —The vertical of any observer is thedirection of a plumb line…
Astronomy
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