The nearest pair revolve around their common center in about fifty-eight years, while the third star revolves with the other two, around a center common to all three, in a period of six or seven hundred years. But the movements of the third star are erratic, and inexplicable except upon the hypothesis advanced by Seeliger, that there is an invisible, or dark, star near it by whose attraction its motion is perturbed.
In endeavoring to picture the condition of things in ζ Cancri we might imagine our sun to have a companion sun, a half or a third as large as itself, and situated within what may be called planetary distance, circling with it around their center of gravity; while a third sun, smaller than the second and several times as far away, and accompanied by a black or non-luminous orb, swung with the first two around another center of motion. There you would have an entertaining complication for the inhabitants of a system of planets!
Other objects in Cancer are: Σ 1223, double star, magnitudes six and six and a half, distance 5″, p. 214°; Σ 1291, double, magnitudes both six, distance 1·3″, p. 328°—four-inch should split it; ι, double, magnitudes four and a half and six and a half, distance 30″, p. 308°; 66, double, magnitudes six and nine, distance 4·8″, p. 136°; Σ 1311, double, magnitudes both about the seventh, distance 7″, p. 200°; 1712, star cluster, very beautiful with the five-inch glass.
The constellation of Auriga may next command our attention (map No. 5). The calm beauty of its leading star Capella awakens an admiration that is not diminished by the rivalry of Orion's brilliants glittering to the south of it. Although Capella must be an enormously greater sun than ours, its spectrum bears so much resemblance to the solar spectrum that a further likeness of condition is suggested. No close companion to Capella has been discovered, and it is not probable that any exists except, possibly, in the form of planets which no telescope can reveal. A ninth-magnitude companion, distant 159″, p. 146°, and two others, one of twelfth magnitude at 78″, p. 317°, and the other of thirteenth magnitude at 126″, p. 183°, may be distant satellites of the great star, but not planets in the ordinary sense, since it is evident that they are self-luminous. It isfact that most of the first-magnitude stars have faint companions which are not so distant as altogether to preclude the idea of physical relationship.
While we are in Auriga we must look at the star β (Menkalina), which belongs to a peculiar order of double stars discovered within the past few years. But neither our telescopes, nor any telescope in existence, can directly reveal the duplicity of β Aurigæ to the eye—i. e., we can not see the two stars composing it.