Recreations in Astronomy Part 15

Procyon moves in an orbit which requires the presence of a companion star, but it has as yet eluded our search. Castor is a double star; but a third star or planet, as yet undiscovered, is required to account for its perturbations. Men who discovered Neptune by the perturbations of Ura.n.u.s are capable of judging the cause of the perturbations of suns. We have spoken of [Page 212] the whole orbit of the earth being invisible from the stars. The nearest star in our northern hemisphere, 61 Cygni, is a telescopic double star; the const.i.tuent parts of it are forty-five times as far from each other as the earth is from the sun, yet it takes a large telescope to show any distance between the stars.[*]

[Footnote *: _Telescopic Work._--Only such work will be laid out here as can be done by small telescopes of from two to four inch object-gla.s.ses. The numbers in Fig. 75 correspond to those of the table.

-------------------------------------------------------------------- Dist. of Magni- No. Name. Fig. Parts. tudes. Remarks. --- ------------ ------------- -------- ------ --------------------- 1. e Lyrae 72 1' 56" Quadruple. 2. z Lyrae 72 44 5 & 6 Topaz and green. 3. b Cygni 73 34-1/2 3 & 6 Yellow and blue. 4. 61 Cygni 73 20 5 & 6 Nearest star but one. 5. Mizar 67 14 3 & 4 Both white. 6. Polaris 67 18-1/2 2 & 9 Test object of eye and gla.s.s. 7. r Orionis Frontispiece. 7 5 & 8 Yellow and blue. 8. b Orionis " 9 1 & 8 Rigel. 9. d " " 10 2 & 8 Red and white. 10. th " " Septuple. 11. l " " 5 White and violet. 12. s " " A, B. 11 4 & 10 Octuple. 13. Castor 69 5-1/2 2 & 3 White. 14. Pollux 69 Triple Orange, gray, lilac. 15. g Virginis 70 5 3 & 3 Both yellow. -------------------------------------------------------------------- ]

When g Virginis was observed in 1718 by Bradley, the component parts were 7" asunder. He incidentally remarked in his note-book that the line of their connection was parallel to the line of the two stars Spica, or a and d Virginis. By 1840 they were not more than 1" apart, and the line of their connection greatly changed.

The appearance of the star is given in Fig. 75 (15), commencing at the left, for the years 1837 '38 '39 '40 '45 '50 '60 and '79.

also a conjectural [Page 213] orbit, placed obliquely, and the position of the stars at the times mentioned, commencing at the top.

The time of its complete revolution is one hundred and fifty years.

[Ill.u.s.tration: Fig. 75.--Aspects and Revolution of Double Stars.]

The meaning of these double stars is that two or more suns revolve about their centre of gravity, as the moon and earth about their centre. If they have planets, as doubtless they have, the movement is no more complicated than the planets we call satellites of Saturn revolving about their central body, and also about the sun. Kindle Saturn and Jupiter to a blaze, or let out their possible light, and our system would appear a triple star in the distance. Doubtless, in the far past, before these giant planets were cooled, it so appeared.

We find some stars double, others triple, quadruple, octuple, and multiple. It is an extension of the same principles that govern our system. Some of these suns are so far asunder that they can swing their Neptunes between them, with less perturbation than Ura.n.u.s and Neptune have in ours. Light all our planets, and there would be a multiple star with more or less suns seen, [Page 214]

according to the power of the instrument. Perhaps the octuple star s in Orion differs in no respect from our system, except in the size and distance of its separate bodies, and less cooling, either from being younger, or from the larger bodies cooling more slowly.

Suns are of all ages. Infinite variety fills the sky. It is as preposterous to expect that every system or world should have a.n.a.logous circ.u.mstances to ours at the present time, as to insist that every member of a family should be of the same age, and in the same state of development. There are worlds that have not yet reached the conditions of habitability by men, and worlds that have pa.s.sed these conditions long since. Let them go. There are enough left, and an infinite number in the course of preparation. Some are fine and lasting enough to be eternal mansions.

_Colored Stars._

In the cloudy morning we get only red light, but the sun is white.

So Aldebaran and Betelguese may be girt by vapors, that only the strong red rays can pa.s.s. Again, an iron moderately heated gives out dull red light; becoming hotter, it emits white light. Sirius, Regulus, Vega, and Spica may be white from greater intensity of vibration. Procyon, Capella, and Polaris are yellow from less intensity of vibration. Again, burn salt in a white flame, and it turns to yellow; mix alcohol and boracic acid, ignite them, and a beautiful green flame results; alcohol and nitrate of strontia give red flame; alcohol and nitrate of barytes give yellow flame. So the composition of a sun, or the special development of anyone substance thereof at any time, may determine the color of a star.

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The special glory of color in the stars is seen in the marked contrasts presented in the double and multiple stars. The larger star is usually white, still in the intensity of heat and vibration; the others, smaller, are somewhat cooled off, and hence present colors lower down the scale of vibration, as green, yellow, orange, and even red.

That stars should change color is most natural. Many causes would produce this effect. The ancients said Sirius was red. It is now white. The change that would most naturally follow mere age and cooling would be from white, through various colors, to red. We are charmed with the variegated flowers of our gardens of earth, but he who makes the fields blush with flowers under the warm kisses of the sun has planted his wider gardens of s.p.a.ce with colored stars.

"The rainbow flowers of the footstool, and the starry flowers of the throne," proclaim one being as the author of them all.

_Cl.u.s.ters of Stars._

From double and multiple we naturally come to groups and cl.u.s.ters.

Allusion has been made to the Hyades, Pleiades, etc. Everyone has noticed the Milky Way. It seems like two irregular streams of compacted stars. It is not supposed that they are necessarily nearer together than the stars in the spa.r.s.e regions about the pole. But the 18,000,000 suns belonging to our system are arranged within a s.p.a.ce represented by a flattened disk. If one hundred lights, three inches apart, are arranged on a hoop ten feet in diameter, they would be in a circle. Add a thousand or two more the same distance apart, filling up the centre, and [Page 216] extending a few inches on each side of the inner plane of the hoop: an eye in the centre, looking out toward the edge, would see a milky way of lights; looking out toward the sides or poles, would see comparatively few. It would seem as if this oblate spheroidal arrangement was the result of a revolution of all the suns composing the system. Jupiter and earth are flattened at the poles for the same reason.

[Ill.u.s.tration: Fig. 76.--Sprayed Cl.u.s.ter below ae in Hercules.]

[Ill.u.s.tration: Fig. 77.--Globular Cl.u.s.ter.]

In various parts of the heavens there are small globular well-defined cl.u.s.ters, and cl.u.s.ters very irregular in form, marked with sprays of stars. There is a cl.u.s.ter of this latter cla.s.s in Hercules, just under the S, in Fig. 72. "Probably no one ever saw it with a good telescope without a shout of wonder." Here is a cl.u.s.ter of the former cla.s.s represented in Fig. 77. "The n.o.ble globular cl.u.s.ter, o Centauri is beyond all comparison the richest and largest object of the kind in the heavens. Its stars are literally innumerable; and as their total light, when received by the naked eye, affects it hardly more than a star of the fifth to fourth [Page 217]

magnitude, the minuteness of each star may be imagined."

There are two possibilities of thought concerning these cl.u.s.ters.

Either that they belong to our stellar system, and hence the stars must be small and young, or they are another universe of millions of suns, so far way that the inconceivable distances between the stars are shrunken to a hand's-breadth, and their unbearable splendor of innumerable suns can only make a gray haze at the distance at which we behold them. The latter is the older and grander thought; the former the newer and better substantiated.

_Nebulae._

The gorgeous cl.u.s.ters we have been considering appear to the eye or the small telescope as little cloudlets of hazy light. One after another were resolved into stars; and the natural conclusion was, that all would yield and reveal themselves to be cl.u.s.tered suns, when we had telescopes of sufficient power. But the spectroscope, seeing not merely form but substance also, shows that some of them are not stars in any sense, but ma.s.ses of glowing gas. Two of these nebulae are visible to the naked eye: one in Andromeda (see Fig.

68), and one around the middle star of the sword of Orion, shown in Fig.78. A three-inch telescope resolves th Orionis into the famous trapezium, and a nine-inch instrument sees two stars more.

The shape of the nebula is changeable, and is hardly suggestive of the moulding influence of gravitation. It is probably composed of glowing nitrogen and hydrogen gases. Nebulae are of all conceivable shapes--circular, annular, oval, lenticular, [Page 218] conical, spiral, snake-like, looped, and nameless. Compare the sprays of the Crab nebulae above z Tauri, seen in Fig. 79, and the ring nebula, Fig. 80. This last possibly consists of stars, and is situated, as shown in Fig. 81, midway between b and g Lyrae.

[Ill.u.s.tration: Fig. 78.--The great Nebula about the multiple Star th Orionis. (See Frontispiece.)]

When Herschel was sweeping the heavens with his telescope, and saw but few stars, he often said to his a.s.sistant, "Prepare to write; the nebulae are coming." They are most abundant where the stars are least so. A zone about the heavens 30 wide, with the Milky Way in the centre, would include one-fourth of the celestial sphere; but instead of one-fourth, we find nine-tenths [Page 219]

of the stars in this zone, and but one-tenth of the nebulae.

These immense ma.s.ses of unorganized matter are noticed to change their forms, vary their light greatly, but not quickly; they change through the ages. "G.o.d works slowly." He takes a thousand years to lift his hand off.

[Ill.u.s.tration: Fig. 79.--Crab Nebula, near z Tauri. (See Frontispiece.)]

There are many unsolved problems connected with these strange bodies.

Whether they belong to our system, or are beyond it, is not settled; the weight of evidence leans to the first view.

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_Variable Stars._

[Ill.u.s.tration: Fig. 80.--The Ring Nebula.]

Our sun gives a variable amount of light, changing through a period of eleven years. Probably every star, if examined by methods sufficiently delicate and exact, would be found to be variable.

The variations of some [Page 221] stars are so marked as to challenge investigation. b Lyrae (Fig. 81) has two maxima and minima of light. In three days it rises from magnitude 4-1/2 to 3-1/2; in a week falls to 4, and rises to 3-1/2; and in three days more drops to 4-1/2: it makes all these changes in thirteen days; but this period is constantly increasing. The variations of one hundred and forty-three stars have been well ascertained.

[Ill.u.s.tration: Fig. 81.--Constellation Lyra, showing place of the Ring Nebula.]

Mira, or the Wonderful, in the Whale (Fig. 68), is easily found when visible. Align from Capella to the Pleiades, and as much farther, and four stars will be seen, situated thus:

The right-hand one is Mira. For half a month it s.h.i.+nes as a star of the second magnitude. Then for three months it fades away, and lost to sight; going down even to the eleventh magnitude. But after five months its resurrection morning mes; and in three months more--eleven months in all--our Wonderful is in its full glory in the heavens. It its period and brilliancy are also variable.

The star Megrez, d in the Great Bear, has been growing dim [Page 222] for a century. In 1836 Betelguese was exceedingly variable, and continued so till 1840, when the changes became much less conspicuous. Algol (Fig. 68) has been already referred to. This slowly winking eye is of the second magnitude during 2d. 14h. Then it dozes off toward sleep for 4h. 24m., when it is nearly invisible.

It wakes up during the same time; so that its period from maximum brilliancy to the same state again is 2d. 20h. 48m. Its recognizable changes are within five or six hours. As I write, March 25th, 1879, Algol gives its minimum light at 9h. 36m. P.M. It pa.s.ses fifteen minima in 43d. 13m. There will therefore be another minimum May 7th, at 9h. 49m. Its future periods are easy to estimate. Perhaps it has some dark body revolving about it at frightful speed, in a period of less than three days. The period of its variability is growing shorter at an increasing rate. If its variability is caused by a dark body revolving about it, the orbit of that body is contracting, and the huge satellite will soon, as celestial periods are reckoned, commence to graze the surface of the sun itself, rebound again and again, and at length plunge itself into the central fire. Such an event would evolve heat enough to make Algol flame up into a star of the first magnitude, and perhaps out-blaze Sirius or Capella in our winter sky.

None of the causes for these changes we have been able to conjecture seem very satisfactory. The stars may have opaque planets revolving about them, shutting off their light; they may rotate, and have unequally illuminated sides; they may revolve in very elliptical orbits, so as to greatly alter their distance from us; they may be so situated in regard to zones of meteorites as [Page 223] to call down periodically vast showers; but none or all of these suppositions apply to all cases, if they do to any.

_Temporary, New, and Lost Stars._

Besides regular movements to right and left, up and down, to and from us--changes in the intensity of illumination by changes of distance--besides variations occurring at regular and ascertainable intervals, there are stars called _temporary_, s.h.i.+ning awhile and then disappearing; _new_, coming to a definite brightness, and so remaining; and _lost_, those whose first appearance was not observed, but which have utterly disappeared.

In November, 1572, a new star blazed out in Ca.s.siopeia. Its place is shown in Fig. 67, ch g being the stars

d *

g ch

in the seat of the chair, and d being the first one in the back.

This star was visible at noonday, and was brighter than any other star in the heavens. In January, 1573, it was less bright than Jupiter; in April it was below the second magnitude, and the last of May it utterly disappeared. It was as variable in color as in brilliancy. During its first two months, the period of greatest brightness, it was dazzling white, then became yellow, and finally as red as Mars or Aldebaran, and so expired.

A bright star was seen very near to the place of the _Pilgrim_, as the star of 1572 was called, in A.D. 945 and 1264. A star of the tenth magnitude is now seen brightening slowly almost exactly in the same place. It is possible that this is a variable star of a period of about three hundred and ten years, and will blaze out again about 1885.

But we have had, within a few years, fine opportunities [Page 224]