Newcomb, Simon, 1835-1909, Holden, Edward Singleton, 1846-1914, joint author · New York : H. Holt and company · leaf 471
MT. Revolutions of Double Stars—Binary Systems.— Themost interesting question suggested by double stars is thatof their relative motion. It is evident that if thesebodies are endowed with the property of mutual gravita-tion, they must be revolving around each other, as theearth and planets revolve… … Fig. 123.—measukement op P08rnow-ANGi.E. components of the double star is simply the apparentangle which separates them, as seen by the observer. It isalways expressed in seconds or fractions of a second of arc.The angU of position, or position-angle as it is oftencalled for brevity, is the angle…
Astronomy
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