Pleasures of the telescope Part 6

From Lyra we pa.s.s to Cygnus, which, lying in one of the richest parts of the Milky Way, is a very interesting constellation for the possessor of a telescope. Its general outlines are plainly marked for the naked eye by the figure of a cross more than twenty degrees in length lying along the axis of the Milky Way. The foot of the cross is indicated by the star beta, also known as Albireo, one of the most charming of all the double stars. The three-inch amply suffices to reveal the beauty of this object, whose components present as sharp a contrast of light yellow and deep blue as it would be possible to produce artificially with the purest pigments. The magnitudes are three and seven, distance 34.6", p.

55. No motion has been detected indicating that these stars are connected in orbital revolution, yet no one can look at them without feeling that they are intimately related to one another. It is a sight to which one returns again and again, always with undiminished pleasure.

The most inexperienced observer admires its beauty, and after an hour spent with doubtful results in trying to interest a tyro in double stars it is always with a sense of a.s.sured success that one turns the telescope to beta Cygni.

Following up the beam of the imaginary cross along the current of the Milky Way, every square degree of which is here worth long gazing into, we come to a pair of stars which contend for the name-letter chi. On our map the letter is attached to the southernmost of the two, a variable of long period--four hundred and six days--whose changes of brilliance lie between magnitudes four and thirteen, but which exhibits much irregularity in its maxima. The other star, not named but easily recognized in the map, is sometimes called 17. It is an attractive double whose colors faintly reproduce those of beta. The magnitudes are five and eight, distance 26", p. 73. Where the two arms of the cross meet is gamma, whose remarkable _cortege_ of small stars running in curved streams should not be missed. Use the lowest magnifying power.

At the extremity of the western arm of the cross is delta, a close double, difficult for telescopes of moderate aperture on account of the difference in the magnitudes of the components. We may succeed in dividing it with the five-inch. The magnitudes are three and eight, distance 1.5", p. 310. It is regarded as a binary of long and as yet unascertained period.

In omicron^2 we find a star of magnitude four and orange in color, having two blue companions, the first of magnitude seven and a half, distance 107", p. 174, and the second of magnitude five and a half, distance 358", p. 324. Farther north is psi, which presents to us the combination of a white five-and-a-half-magnitude star with a lilac star of magnitude seven and a half. The distance is 3", p. 184. A very pretty sight.

We now pa.s.s to the extremity of the other arm of the cross, near which lies the beautiful little double 49, whose components are of magnitudes six and eight, distance 2.8", p. 50. The colors are yellow and blue, conspicuous and finely contrasted. A neighboring double of similar hues is 52, in which the magnitudes are four and nine, distance 6", p. 60.

Sweeping a little way northward we come upon an interesting binary, lambda, which is unfortunately beyond the dividing power of our largest gla.s.s. A good seven-inch or seven-and-a-half-inch should split it under favorable circ.u.mstances. Its magnitudes are six and seven, distance 0.66", p. 74.

The next step carries us to a very famous object, 61 Cygni, long known as the nearest star in the northern hemisphere of the heavens. It is a double which our three-inch will readily divide, the magnitudes being both six, distance 21", p. 122. The distance of 61 Cygni, according to Hall's parallax of 0.27", is about 70,000,000,000,000 miles. There is some question whether or not it is a binary, for, while the twin stars are both moving in the same direction in s.p.a.ce with comparative rapidity, yet conclusive evidence of orbital motion is lacking. When one has noticed the contrast in apparent size between this comparatively near-by star, which the naked eye only detects with considerable difficulty, and some of its brilliant neighbors whose distance is so great as to be immeasurable with our present means, no better proof will be needed of the fact that the faintness of a star is not necessarily an indication of remoteness.

We may prepare our eyes for a beautiful exhibition of contrasted colors once more in the star . This is really a quadruple, although only two of its components are close and conspicuous. The magnitudes are five, six, seven and a half, and twelve; distances 2.4", p. 121; 208", p. 56; and 35", p. 264. The color of the largest star is white and that of its nearest companion blue; the star of magnitude seven and a half is also blue.

The star cl.u.s.ter 4681 is a fine sight with our largest gla.s.s. In the map we find the place marked where the new star of 1876 made its appearance.

This was first noticed on November 24, 1876, when it shone with the brilliance of a star of magnitude three and a half. Its spectrum was carefully studied, especially by Vogel, and the very interesting changes that it underwent were noted. Within a year the star had faded to less than the tenth magnitude, and its spectrum had completely changed in appearance, and had come to bear a close resemblance to that of a planetary nebula. This has been quoted as a possible instance of a celestial collision through whose effects the solid colliding ma.s.ses were vaporized and expanded into a nebula. At present the star is very faint and can only be seen with the most powerful telescopes. Compare with the case of Nova Aurigae, previously discussed.

Underneath Cygnus we notice the small constellation Vulpecula. It contains a few objects worthy of attention, the first being the nebula 4532, the "dumb-bell nebula" of Lord Rosse. With the four-inch, and better with the five-inch, we are able to perceive that it consists of two close-lying tufts of misty light. Many stars surround it, and large telescopes show them scattered between the two main ma.s.ses of the nebula. The Lick photographs show that its structure is spiral. The star 11 points out the place where a new star of the third magnitude appeared in 1670. Sigma 2695 is a close double, magnitudes six and eight, distance 0.96", p. 78.

[Ill.u.s.tration: MAP NO. 18.]

We turn to map No. 18, and, beginning at the western end of the constellation Aquarius, we find the variable T, which ranges between magnitudes seven and thirteen in a period of about two hundred and three days. Its near neighbor Sigma 2729 is a very close double, beyond the separating power of our five-inch, the magnitudes being six and seven, distance 0.6", p. 176. Sigma 2745, also known as 12 Aquarii, is a good double for the three-inch. Its magnitudes are six and eight, distance 2.8", p. 190. In zeta we discover a beauty. It is a slow binary of magnitudes four and four, distance 3.1", p. 321. According to some observers both stars have a greenish tinge. The star 41 is a wider double, magnitudes six and eight, distance 5", p. 115, colors yellow and blue. The uncommon stellar contrast of white with light garnet is exhibited by tau, magnitudes six and nine, distance 27", p. 115. Yellow and blue occur again conspicuously in psi, magnitudes four and a half and eight and a half, distance 50", p. 310. Rose and emerald have been recorded as the colors exhibited in Sigma 2998, whose magnitudes are five and seven, distance 1.3", p. 346.

The variables S and R are both red. The former ranges between magnitudes eight and twelve, period two hundred and eighty days, and the latter between magnitudes six and eleven, period about three hundred and ninety days.

The nebula 4628 is Rosse's "Saturn nebula," so called because with his great telescope it presented the appearance of a nebulous model of the planet Saturn. With our five-inch we see it simply as a planetary nebula. We may also glance at another nebula, 4678, which appears circular and is pinned with a little star at the edge.

The small constellation Equuleus contains a surprisingly large number of interesting objects. Sigma 2735 is a rather close double, magnitudes six and eight, distance 1.8", p. 287. Sigma 2737 (the first star to the left of Sigma 2735, the name having accidentally been omitted from the map) is a beautiful triple, although the two closest stars, of magnitudes six and seven, can not be separated by our instruments. Their distance in 1886 was 0.78", p. 286, and they had then been closing rapidly since 1884, when the distance was 1.26". The third star, of magnitude eight, is distant 11", p. 75. Sigma 2744 consists of two stars, magnitudes six and seven, distance 1.4", p. 1.67. It is probably a binary. Sigma 2742 is wider double, magnitudes both six, distance 2.6", p. 225. Another triple, one of whose components is beyond our reach, is gamma. Here the magnitudes are fifth, twelfth, and sixth, distances 2", p. 274 and 366". It would also be useless for us to try to separate delta, but it is interesting to remember that this is one of the closest of known double stars, the magnitudes being fourth and fifth, distance 0.4", p. 198. These data are from Hall's measurements in 1887. The star is, no doubt, a binary. With the five-inch we may detect one and perhaps two of the companion stars in the quadruple beta.

The magnitudes are five, ten, and two eleven, distances 67", p. 309; 86", p. 276; and 6.5", p. 15. The close pair is comprised in the tenth-magnitude star.

[Ill.u.s.tration: MAP NO. 19.]

Map No. 19 introduces us to the constellation Pegasus, which is comparatively barren to the naked eye, and by no means rich in telescopic phenomena. The star epsilon, of magnitude two and a half, has a blue companion of the eighth magnitude, distance 138", p. 324; colors yellow and violet. A curious experiment that may be tried with this star is described by Webb, who ascribes the discovery of the phenomenon to Sir John Herschel. When near the meridian the small star in epsilon appears, in the telescope, underneath the large one. If now the tube of the telescope be slightly swung from side to side the small star will appear to describe a pendulumlike movement with respect to the large one. The explanation suggested is that the comparative faintness of the small star causes its light to affect the retina of the eye less quickly than does that of its brighter companion, and, in consequence, the reversal of its apparent motion with the swinging of the telescope is not perceived so soon.

The third-magnitude star eta has a companion of magnitude ten and a half, distance 90", p. 340. The star beta, of the second magnitude, and reddish, is variable to the extent of half a magnitude in an irregular period, and gamma, of magnitude two and a half, has an eleventh-magnitude companion, distance 162", p. 285.

[Ill.u.s.tration: MAP NO. 20.]

Our interest is revived on turning, with the guidance of map No. 20, from the comparative poverty of Pegasus to the s.p.a.cious constellation Cetus. The first double star that we meet in this constellation is 26, whose components are of magnitudes six and nine, distance 16.4", p.

252; colors, topaz and lilac. Not far away is the closer double 42, composed of a sixth and a seventh magnitude star, distance 1.25", p.

350. The four-inch is capable of splitting this star, but we shall do better to use the five-inch. In pa.s.sing we may glance at the tenth-magnitude companion to eta, distance 225", p. 304. Another wide pair is found in zeta, magnitudes three and nine, distance 185", p. 40.

The next step brings us to the wonderful variable omicron, or Mira, whose changes have been watched for three centuries, the first observer of the variability of the star having been David Fabricius in 1596. Not only is the range of variability very great, but the period is remarkably irregular. In the time of Hevelius, Mira was once invisible for four years. When brightest, the star is of about the second magnitude, and when faintest, of the ninth magnitude, but at maximum it seldom exhibits the greatest brilliance that it has on a few occasions shown itself capable of attaining. Ordinarily it begins to fade after reaching the fourth or fifth magnitude. The period averages about three hundred and thirty-one days, but is irregularly variable to the extent of twenty-five days. Its color is red, and its spectrum shows bright lines, which it is believed disappear when the star sinks to a minimum.

Among the various theories proposed to account for such changes as these the most probable appears to be that which ascribes them to some cause a.n.a.logous to that operating in the production of sun spots. The outburst of light, however, as pointed out by Scheiner, should be regarded as corresponding to the maximum and not the minimum stage of sun-spot activity. According to this view, the star is to be regarded as possessing an extensive atmosphere of hydrogen, which, during the maximum, is upheaved into enormous prominences, and the brilliance of the light from these prominences suffices to swamp the photospheric light, so that in the spectrum the hydrogen lines appear bright instead of dark.

It is not possible to suppose that Mira can be the center of a system of habitable planets, no matter what we may think of the more constant stars in that regard, because its radiation manifestly increases more than six hundred fold, and then falls off again to an equal extent once in every ten or eleven months. I have met people who can not believe that the Almighty would make a sun and then allow its energies "to go to waste," by not supplying it with a family of worlds. But I imagine that if they had to live within the precincts of Mira Ceti they would cry out for exemption from their own law of stellar utility.

The most beautiful double star in Cetus is gamma, magnitudes three and seven, distance 3", p. 288; hues, straw-color and blue. The leading star alpha, of magnitude two and a half, has a distant blue companion three magnitudes fainter, and between them are two minute stars, the southernmost of which is a double, magnitudes both eleven, distance 10", p. 225.

The variable S ranges between magnitudes seven and twelve in a somewhat irregular period of about eleven months, while R ranges between the seventh and the thirteenth magnitudes in a period of one hundred and sixty-seven days.

[Ill.u.s.tration: MAP NO. 21.]

The constellation Erida.n.u.s, represented in map No. 21, contains a few fine double stars, one of the most interesting of which is 12, a rather close binary. The magnitudes are four and eight, distance 2", p. 327.

We shall take the five-inch for this, and a steady atmosphere and sharp seeing will be necessary on account of the wide difference in the brightness of the component stars. Amateurs frequently fail to make due allowance for the effect of such difference. When the limit of separating power for a telescope of a particular aperture is set at 1"

or 2", as the case may be, it is a.s.sumed that the stars composing the doubles on which the test is made shall be of nearly the same magnitude, or at least that they shall not differ by more than one or two magnitudes at the most. The stray light surrounding a comparatively bright star tends to conceal a faint companion, although the telescope may perfectly separate them so far as the stellar disks are concerned.

Then, too, I have observed in my own experience that a very faint and close double is more difficult than a brighter pair not more widely separated, usually on account of the defect of light, and this is true even when the components of the faint double are of equal magnitude.

Sigma 470, otherwise known as 32 Eridani, is a superb object on account of the colors of its components, the larger star being a rich topaz and the smaller an ultramarine; while the difference in magnitude is not as great as in many of the colored doubles. The magnitudes are five and seven, distance 6.7", p. 348. The star gamma, of magnitude two and a half, has a tenth-magnitude companion, distant 51", p. 238. Sigma 516, also called 39 Eridani, consists of two stars of magnitudes six and nine, distance 6.4", p. 150; colors, yellow and blue. The supposed binary character of this star has not yet been established.

In omicron^2 we come upon an interesting triple star, two of whose components at any rate we can easily see. The largest component is of the fourth magnitude. At a distance of 82", p. 105, we find a tenth-magnitude companion. This companion is itself double, the magnitudes of its components being ten and eleven, distance 2.6", p.

98. Hall says of these stars that they "form a remarkable system." He has also observed a fourth star of the twelfth magnitude, distant 45"

from the largest star, p. 85. This is apparently unconnected with the others, although it is only half as distant as the tenth-magnitude component is from the primary. Sigma 590 is interesting because of the similarity of its two components in size, both being of about the seventh magnitude, distance 10", p. 318.

Finally, we turn to the nebula 826. This is planetary in form and inconspicuous, but La.s.sell has described it as presenting a most extraordinary appearance with his great reflector--a circular nebula lying upon another fainter and larger nebula of a similar shape, and having a star in its center. Yet it may possibly be an immensely distant star cl.u.s.ter instead of a nebula, since its spectrum does not appear to be gaseous.

CHAPTER VII

PISCES, ARIES, TAURUS, AND THE NORTHERN STARS

"Now sing we stormy skies when Autumn weighs The year, and adds to nights and shortens days, And suns declining s.h.i.+ne with feeble rays."--DRYDEN'S VIRGIL.

[Ill.u.s.tration: MAP NO. 22.]

The eastern end of Pisces, represented in map No. 22, includes most of the interesting telescopic objects that the constellation contains. We begin our exploration at the star numbered 55, a double that is very beautiful when viewed with the three-inch gla.s.s. The components are of magnitudes five and eight, distance 6.6", p. 192. The larger star is yellow and the smaller deep blue. The star 65, while lacking the peculiar charm of contrasted colors so finely displayed in 55, possesses an attraction in the equality of its components which are both of the sixth magnitude and milk-white. The distance is 4.5", p. 118. In 66 we find a swift binary whose components are at present far too close for any except the largest telescopes. The distance in 1894 was only 0.36", p. 329. The magnitudes are six and seven. In contrast with this excessively close double is psi, whose components are both of magnitude five and a half, distance 30", p. 160. Dropping down to 77 we come upon another very wide and pleasing double, magnitudes six and seven, distance 33", p. 82, colors white and lilac or pale blue. Hardly less beautiful is zeta magnitudes five and six, distance 24", p. 64. Finest of all is alpha, which exhibits a remarkable color contrast, the larger star being greenish and the smaller blue. The magnitudes are four and five, distance 3", p. 320. This star is a binary, but the motion is slow. The variable R ranges between magnitudes seven and thirteen, period three hundred and forty-four days.

The constellation Aries contains several beautiful doubles, all but one of which are easy for our smallest aperture. The most striking of these is gamma, which is historically interesting as the first double star discovered. The discovery was made by Robert Hooke in 1664 by accident, while he was following the comet of that year with his telescope. He expressed great surprise on noticing that the gla.s.s divided the star, and remarked that he had not met with a like instance in all the heavens. His observations could not have been very extensive or very carefully conducted, for there are many double stars much wider than gamma Arietis which Hooke could certainly have separated if he had examined them. The magnitudes of the components of gamma are four and four and a half, or, according to Hall, both four; distance 8.5", p.

180. A few degrees above gamma, pa.s.sing by beta, is a wide double lambda, magnitudes five and eight, distance 37", p. 45, colors white and lilac or violet. Three stars are to be seen in 14: magnitudes five and a half, ten, and nine, distances 83", p. 36, and 106", p. 278, colors white, blue, and lilac. The star 30 is a very pretty double, magnitudes six and seven, distance 38.6", p. 273. Sigma 289 consists of a topaz star combined with a sapphire, magnitudes six and nine, distance 28.5", p. 0. The fourth-magnitude star 41 has several faint companions.

The magnitudes of two of these are eleven and nine, distances 34", p.

203, and 130", p. 230. We discover another triple in pi, magnitudes five, eight, and eleven, distances 3.24", p. 122, and 25", p. 110. The double mentioned above as being too close for our three-inch gla.s.s is epsilon, which, however, can be divided with the four-inch, although the five-inch will serve us better. The magnitudes are five and a half and six, distance 1.26", p. 202. The star 52 has two companions, one of which is so close that our instruments can not separate it, while the other is too faint to be visible in the light of its brilliant neighbor without the aid of a very powerful telescope.

[Ill.u.s.tration: MAP NO. 23.]

We are now about to enter one of the most magnificent regions in the sky, which is hardly less attractive to the naked eye than Orion, and which men must have admired from the beginning of their history on the earth, the constellation Taurus (map No. 23). Two groups of stars especially distinguish Taurus, the Hyades and the Pleiades, and both are exceedingly interesting when viewed with the lowest magnifying powers of our telescopes.

We shall begin with a little star just west of the Pleiades, Sigma 412, also called 7 Tauri. This is a triple, but we can see it only as a double, the third star being exceedingly close to the primary. The magnitudes are six and a half, seven, and ten, distances 0.3", p. 216, and 22", p. 62. In the Pleiades we naturally turn to the brightest star eta, or Alcyone, famous for having once been regarded as the central sun around which our sun and a mult.i.tude of other luminaries were supposed to revolve, and picturesque on account of the little triangle of small stars near it which the least telescopic a.s.sistance enables us to see.

One may derive much pleasure from a study of the various groupings of stars in the Pleiades. Photography has demonstrated, what had long been suspected from occasional glimpses revealed by the telescope, that this celebrated cl.u.s.ter of stars is intermingled with curious forms of nebulae. The nebulous matter appears in festoons, apparently attached to some of the larger stars, such as Alcyone, Merope, and Maia, and in long, narrow, straight lines, the most remarkable of which, a faintly luminous thread starting midway between Maia and Alcyone and running eastward some 40', is beaded with seven or eight stars. The width of this strange nebulous streak is, on an average, 3" or 4", and there is, perhaps, no more wonderful phenomenon anywhere in celestial s.p.a.ce.

Unfortunately, no telescope is able to show it, and all our knowledge about it is based upon photographs. It might be supposed that it was a nebulous disk seen edgewise, but for the fact that at the largest star involved in its course it bends sharply about 10 out of its former direction, and for the additional fact that it seems to take its origin from a curved offshoot of the intricate nebulous ma.s.s surrounding Maia.

Exactly at the point where this curve is transformed into a straight line s.h.i.+nes a small star! In view of all the facts the idea does not seem to be very far-fetched that in the Pleiades we behold an a.s.semblage of suns, large and small, formed by the gradual condensation of a nebula, and in which evolution has gone on far beyond the stage represented by the Orion nebula, where also a group of stars may be in process of formation out of nebulous matter. If we look a little farther along this line of development, we may perceive in such a stellar a.s.semblage as the cl.u.s.ter in Hercules, a still later phase wherein all the originally scattered material has, perhaps, been absorbed into the starry nuclei.

[Ill.u.s.tration: THE CHIEF STARS IN THE PLEIADES.]

The yellow star Sigma 430 has two companions: magnitudes six, nine, and nine and a half, distances 26", p. 55, and 39", p. 302. The star 30 of the fifth magnitude has a companion of the ninth magnitude, distance 9", p. 58, colors emerald and purple, faint. An interesting variable, of the type of Algol, is lambda, which at maximum is of magnitude three and four tenths and at minimum of magnitude four and two tenths. Its period from one maximum to the next is about three days and twenty-three hours, but the actual changes occupy only about ten hours, and it loses light more swiftly than it regains it. A combination of red and blue is presented by Phi (mistakenly marked on map No. 23 as psi). The magnitudes are six and eight, distance 56", p. 242. A double of similar magnitudes is chi, distance 19", p. 25. Between the two stars which the naked eye sees in kappa is a minute pair, each of less than the eleventh magnitude, distance 5", p. 324. Another naked-eye double is formed by theta^1 and theta^2, in the Hyades. The magnitudes are five and five and a half, distance about 5' 37".