Newcomb, Simon, 1835-1909, Holden, Edward Singleton, 1846-1914, joint author · New York, H. Holt and Company · leaf 469
Y. Revolutions of Double Stars—Binary Systems.— The most 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.—measurement of position-angle. components of the double star is simply the apparentangle which separates them, as seen by the observer. It isalways expressed in seconds of fractions of a second of arc.The angle af position, or ^ position-angle as it is oftencalled for brevity, is the…
Astronomy
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