CHAPTER III.

DOUBLE, VARIABLE, AND TEMPORARY STARS, BINARY SYSTEMS, ETC

415. MANY of the stars which, to the naked eye, appear single, are found, when examined by the aid of a telescope, to consist of two or more stars, in a state of near proximity to each other. These are called Double Stars. When three or more stars are found thus closely connected, they are called Triple or Multiple Stars.

416. Double and triple stars are supposed to be constituted in two ways-first, by actual contiguity; and secondly, where they are only near the same line of vision, one of the component stars being far beyond the other. In the former case, they are said to be physically double, from the belief that they are bound together by attraction, and that one revolves around the other; while in the latter case, they are considered as only optically double.

Here the observer on the left sces a large and small star at A, apparently near toge ther the lowest star being much the smallest. But instead of their being situated as they appear to be, with respect to each other, the true position of the smaller star may be at B instead of A; and the difference in their apparent magnitudes may be wholly owing to the greater distance of the lower star.

Upon this subject Dr. Herschel remarks, that this nearness of the stars to each other, in certain cases, might be attributed to some accidental cause, did it occur only in a few instances; but the frequency of this companionship, the extreme closeness, and, in many cases, the near equality of the stars so conjoined, would alone lead to a strong suspicion of a more near and intimate relation than mere casual juxtaposition.

415. What said of double, triple, and multiple stars?

416. How are they supposed to be constituted? How distinguished? (Illustrate by diagram. Remark of Dr. Herschel? How many specimens of double stars given?)

The following will convey to the student an idea of the telescopic appearance of some of the double stars:

417. A is a double star in Ursa Minor, commonly known as the Pole star. It consists of a star of the 2d, and another of the 9th magnitude, situated about 18" apart, or about four times the diameter of the larger star. They are both of a silvery white. It requires a pretty good telescope to show this star double; hence it is considered a very good test object by which to ascertain the qualities of a telescope, especially of the lowpriced refractors.

The writer has often seen the companion of the Pole star distinctly, with a six-inch refracting telescope, manufactured by Mr. Henry Fitz, New York.

418. B is a view of the double star Castor, in the Twins. The stars are of a greenish white, of the 3d and 4th magnitudes, and about 5", or two diameters of the principal star, apart. This also is considered a good test object. Through ordinary telescopes, the stars seem to be in contact; but with those of higher power, they appear fairly divided. These stars constitute what is called a Binary System.

419. C is a representation of Mizar, the middle star, in the tail of the Great Bear. It may be seen double with a good spy-glass. The stars are both of a greenish white, of the 3d and 4th magnitudes, and about 14' apart. Mizar has sometimes been seen without a companion, and at other times it has been known suddenly to appear. The companion is not Alcor, near Mizar, and visible to the naked eye, but a telescopic star.

417. What is Fig. A in the cut? (Remark of author in note?)

418. Fig. B-color? Magnitudes? 419. Fig. C-how seen? Color? remarks?

How composed? Color? How seen?

Distance apart? Further remark?
Magnitude? Distance? Additional

420. D is a view of the double star Mintaka, the middle star of the three forming the belt of Orion. The component stars are of the 4th and 8th magnitudes-the largest of a reddish hue, and the small one white. They are about 10" apart, or four times the diameter of the largest star.

421. E is a view of Rigel, in the left foot of Orion. The components are of the 1st and 9th magnitudes, and about 10" apart. Their color is a yellowish white.

422. F is a view of the bright star Vega, in the Lyre. Its companion is a star of the 11th magnitude, situated about 40" distant. This is a close test object for an ordinary telescope.

423. The number of double stars has been variously estimated. Sir William Herschel enumerates upwards of 500, the individuals of which are within 30′′ of each other. Professor Struve of Dorpat estimated the number at about 3,000; and more recent observations fix the number at not less than 6,000. The great number of the double stars first led astronomers to suspect a physical connection by the laws of gravitation, and also a revolution of star around star, as the planets revolve around the sun.

BINARY AND OTHER SYSTEMS.

424. By carefully noting the relative distances and angular positions of double and multiple stars, for a series of years, it has been found that many of them have their periodic revolutions around each other. Where two stars are found in a state of revolution about a common center, they constitute what is called a Binary System. These, it must be remembered, are the double and multiple stars, which appear single to the naked eye. Sir W. Herschel noticed about 50 instances of changes in the angular position of double stars; and the revolu

420. Fig. D-describe. Magnitude? Color? Distance? 421. Fig. E-place? Components? Distance? Color?

422. Fig. F-companion?

423. Number of double stars? Led to what?

424. Motions of double stars?

What are binary systems?

tion of some eighteen of these is considered certain. Their periods vary from 40 to 1,200 years.

425. The star numbered 70 in the Serpent-bearer is a binary system. The periodic time of the revolving star is about 93 years. In the course of its revolution, the two stars sometimes appear separated, sometimes very near together, and at other times as one star. They are of the 5th and 6th magnitudes, and of a yellowish hue.

426.. The star, in the left hind paw of Ursa Major, is one of these stellar systems. The revolution of its component stars began to be noticed in 1781; since which time they have made one complete revolution, and are now (1853) some fourteen years on the second. Of course, then, their periodic time is about 58 years. Their angular motion is about 6° 24′ per year.

Dr. Dick supposes these stars to be some 200,000,000,000 miles apart; and upon the supposition that the smaller revolves around the latter, computes its velocity to be not less than 2,471,000 miles every hour. This would be 85 times the velocity of Jupiter and 23 times the velocity of Mercury-the swiftest planet in the solar system.

427. The star y in Virgo is another of these systems. It has been known as a double star for at least 130 years. The two stars are both of the 3d magnitude, and of a yellowish color. The late E. P. Mason, of Yale College, estimated its period at 171 years. More recent observa tions and estimates by Mädler give a period of 145 years.

428. "To some minds, not accustomed to deep reflec tion," says Dr. Dick, "it may appear a very trivial fact to behold a small and scarcely distinguishable point of light immediately adjacent to a larger star, and to be informed that this lucid point revolves around its larger attendant; but this phenomenon, minute and trivial as it may at first sight appear, proclaims the astonishing fact, that suns revolve around suns, and systems around systems. This is a comparatively new idea, derived from our late sidereal investigations, and forms one of the

425. Describe 70 Ophiuchi?

426. What specimen described? Period? Yearly angular motion? (Dr. Dick's remark?)

427. What other binary system? How long known? Components? Period?

428. Quotation from Dr. Dick.

most sublime conceptions which the modern discoveries of astronomy have imparted.

429. "It undoubtedly conveys a very sublime idea, to contemplate such a globe as the planet Jupiter—a body thirteen hundred times larger than the earth-revolving around the sun, at the rate of twenty-nine thousand miles every hour; and the planet Saturn, with its rings and moons, revolving in a similar manner round this central orb, in an orbit five thousand six hundred and ninety millions of miles in circumference. But how much more august and overpowering the conception of a sun revolving around another sun-of a sun encircled with a retinue of huge planetary bodies, all in rapid motion, revolving round a distant sun, over a circumference a hundred times larger than what has been now stated, and with a velocity perhaps a hundred times greater than that of either Jupiter or Saturn, and carrying all its planets, satellites, comets, or other globes, along with it in its swift career! Such a sun, too, may as far exceed these planets in size as our sun transcends in magnitude either this earth or the planet Venus; the bulk of any one of which scarcely amounts to the thirteen-hundredthousandth part of the solar orb which enlightens our day.

430. "The further we advance in our explorations of the distant regions of space, and the more minute and specific our investigations are, the more august and astonishing are the scenes which open to our view, and the more elevated do our conceptions become of the grandeur of that Almighty Being who marshalled all the starry hosts,' and of the multiplicity and variety of arrangements he has introduced into his vast creation. And this consideration ought to serve as an argument to every rational being, both in a scientific and a religious point of view, to stimulate him to a study of the operations of the Most High, who is wonderful in counsel, and excellent in working,' and whose works in every

429. What further remarks?

430. Continue quotation. (What table? Note?)