One of the most interesting of triple stars is the tricoloured γ Andromedæ. 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 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 have appeared most perplexing, and complicated beyond precedent. ‘If this be really a ternary system,’ wrote Sir John Herschel, ‘connected by the mutual attraction of its parts, its perturbations will present one of the most intricate problems in physical astronomy.’ The second star revolves round its primary, whilst the third pursues a retrograde course, but its path, instead of being even, presents the appearance of a series of circular loopings, in traversing which the star alternately quickens and slackens its pace, or at times appears to be stationary.
Astronomers have arrived at the conclusion that these perturbations are produced by the presence of a fourth member, which, though invisible, is probably the most massive of the system—perhaps a magnificent world teeming with animated beings, and attended by three suns which gravitate round it, dispensing light and heat to meet the requirements of the various forms of life which exist on its surface. In this system we have an arrangement the reverse of what exists in the solar system, where all the planets revolve round a predominant sun; but here there is a strange verification of the old Ptolemaic belief with regard to the path of a sun, though in this instance there are three suns circling round a dark globe which they illumine and vivify.
Triple stars occur with comparative frequency throughout the heavens. In Monoceros there is a fine triple star, discovered by Herschel, which he describes as ‘one of the most beautiful sights in the heavens.’ The stars ξ and β Scorpii form triple systems in which the components are differently arranged. In ξ the primary and secondary consist of two revolving stars which control the movements of a distant attendant; in β the primary and secondary stars are in mutual revolution, whilst round the former there circles a very close minute companion. There are doubtless many binary stars which, if examined with adequate telescopic power, would resolve themselves into triple and multiple systems, but the profound distances of those objects render the detection of their components a most difficult task.
Quadruple stars are usually arranged in pairs, i.e. the primary and secondary of a binary system are each resolvable into two, forming two pairs, each pair being in mutual revolution, while they both gravitate round their common centre of gravity. ε Lyræ, which has been described as a double double, is an example of a quadruple system, and ν Scorpii is of a similar construction, but more beautiful because its components are in closer proximity to each other. Close upon twenty of those double double systems have been discovered in different parts of the heavens.
One of the most interesting of quadruple systems is θ Orionis, which is situated in the Great Nebula, by which it is surrounded. This star, when observed with a telescope of low power, can be at once resolved into four separate lucent points, so arranged as to form a quadrilateral figure or trapezium. They are of the fifth, sixth, seventh, and eighth magnitudes, and described as pale white, garnet, faint lilac, and red. Though they have been under careful observation for upwards of two centuries, no perceptible motion has been perceived as occurring among them, nor has there been any change in their relative positions—they appear to be perfectly motionless; but we must not infer from this that no physical bond of union exists between them, for they are situated at an amazing distance from the Earth. Ascending higher in the scale of celestial architecture, we have multiple stars forming systems still more elaborate and complex, into the structure of which numerous stars enter, and they, as they increase in number, gradually merge into star-clusters.
If we assume that around each of the components of a multiple star there circles a retinue of planetary worlds, we are confronted with a most perplexing problem as to how the dynamical stability of a system so different from, and so vastly more complicated than, that of our solar system is maintained—where, as it were, suns and planets intermingle—how numerous circling orbs can accomplish their revolutions without being swayed and deflected from their paths by the gravitational attraction of adjacent members of the same system. Perplexing though the arrangement of such a scheme may be to our conception, yet, each orb has been weighed, poised, and adjusted by Infinite Wisdom, to perform its intricate motions in synchronous harmony with other members of the system—all moving in unison like the parts of a complicated piece of mechanism, and maintained in stable equilibrium by their mutual attraction—
Mystical dance, which yonder starry sphere
Of planets and of fixed in all her wheels
Resembles nearest; mazes intricate,
Eccentric, intervolved, yet regular
Then most, when most irregular they seem;
And in their motions harmony divine
So smooths her charming tones that God’s own ear
Listens delighted.—v. 620-27.
All the natural phenomena with which we are familiar would, in the case of planets revolving round the component suns of a multiple system, be of a different kind or altogether absent. Instead of being illumined by one sun, those worlds would, at certain times, have several suns—some more distant than others—above their horizons, and upon very rare occasions, if ever, would there be an entire absence of all of those orbs from their skies. Consequently there would be no year such as we are familiar with; no regular sequence of seasons similar to what is experienced on Earth; no alternation of day and night, for there would be ‘no night there,’ though, in the absence of the primary orb, the light emitted by distant suns, whilst sufficient to banish night, and beyond comparison brighter than the Moon when at full, would, in the diminution of its intensity from that of noonday, be as grateful a change as that of from day to night which occurs on our globe.
Should those suns be differently coloured, each emitting its own peculiar shade of light as it appears above the horizon, the varied aspects of the perpetual day enjoyed by the inhabitants of those circling worlds present to the imagination harmonies of light and shade over which it is pleasant to linger.