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The Astronomy of Milton's 'Paradise Lost'
written by "Orchard, Thomas Nathaniel"
...and form systems of a more complex character than what are observed in the case of binary stars. In the usual construction of a triple system, the secondary star of a binary is resolvable into two, each star being in mutual revolution, whilst they both gravitate round their primary. By another arrangement, a close pair control the movements of a distant attendant. One of the most interesting of triple stars is the tricoloured γ Andromed. The brilliant components of this system have their counterparts in the topaz, the emerald, and the sapphire—the larger star is of the third magnitude and of a golden yellow colour; the secondary of the fifth magnitude and of an emerald green. These stars are ten seconds apart, and, though they have been under observation since 1777, no orbital movement has as yet been detected, but their common proper motion indicates[Pg 201] their close relationship and physical connection. In 1842, Otto Struve discovered that the companion star is itself double, and round it there gravitates a sapphire sun, which is believed to accomplish a revolution of its orbit in about 500 years. If round those suns there should be circling planetary systems of worlds inhabited by intelligent beings, the varied effects produced by the light emanating from those different coloured orbs would be of a very beautiful and pleasing nature. A system suggestive of the endless variety of stellar arrangement that exists throughout the sidereal regions is apparent in the case of the triple star ζ Cancri. Two of the stars, of magnitudes six and seven, form a binary in rapid revolution, the components of which complete a circuit of their orbits in fifty-eight years, whilst the more distant third star, of almost similar magnitude, accomplishes a wide orbital ellipse round the other two in 500 or 600 years. These stars have been closely observed by astronomers during the past forty years, with the result that their motions h...

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