Pleasures of the telescope Part 7

The leading star of Taurus, Aldebaran (alpha), is celebrated for its reddish color. The precise hue is rather uncertain, but Aldebaran is not orange as Betelgeuse in Orion is, and no correct eye can for an instant confuse the colors of these two stars, although many persons seem to be unable to detect the very plain difference between them in this respect.

Aldebaran has been called "rose-red," and it would be an interesting occupation for an amateur to determine, with the aid of some proper color scale, the precise hue of this star, and of the many other stars which exhibit chromatic idiosyncrasy. Aldebaran is further interesting as being a standard first-magnitude star. With the four-inch gla.s.s we see without difficulty the tenth-magnitude companion following Aldebaran at a distance of 114", p. 35. There is an almost inexplicable charm about these faint attendants of bright stars, which is quite different from the interest attaching to a close and nearly equal pair. The impression of physical relations.h.i.+p is never lacking though it may be deceptive, and this awakens a lively appreciation of the vast differences of magnitude that exist among the different suns of s.p.a.ce.

The actual size and might of this great red sun form an attractive subject for contemplation. As it appears to our eyes Aldebaran gives one twenty-five-thousand-millionth as much light as the sun, but if we were placed midway between them the star would outs.h.i.+ne the sun in the ratio of not less than 160 to 1. And yet, gigantic as it is, Aldebaran is possibly a pygmy in comparison with Arcturus, whose possible dimensions were discussed in the chapter relating to Bootes. Although Aldebaran is known to possess several of the metallic elements that exist in the sun, its spectrum differs widely from the solar spectrum in some respects, and more closely resembles that of Arcturus.

Other interesting objects in Taurus are sigma, divisible with the naked eye, magnitudes five and five and a half, distance 7'; Sigma 674, double, magnitudes six and nine, distance 10.5", p. 147; Sigma 716, double, magnitudes six and seven, distance 5", p. 200--a pleasing sight; tau, triple, magnitudes four, ten and a half, and eleven, distances 36", p. 249, and 36", p. 60--the ten-and-a-half-magnitude star is itself double, as discovered by Burnham; star cl.u.s.ter No. 1030, not quite as broad as the moon, and containing some stars as large as the eleventh magnitude; and nebula No. 1157, the so-called "Crab nebula"

of Lord Rosse, which our gla.s.ses will show only as a misty patch of faint light, although large telescopes reveal in it a very curious structure.

[Ill.u.s.tration: MAP NO. 24.]

We now turn to the cl.u.s.ter of circ.u.mpolar constellations sometimes called the Royal Family, in allusion to the well-known story of the Ethiopian king Cepheus and his queen Ca.s.siopeia, whose daughter Andromeda was exposed on the seash.o.r.e to be devoured by a monster, but who was saved by the hero Perseus. All these mythologic personages are represented in the constellations that we are about to study.[4] We begin with Andromeda (map No. 24). The leading star alpha marks one corner of the great square of Pegasus. The first star of telescopic interest that we find in Andromeda is , a double difficult on account of the faintness of the smaller component. The magnitudes are four and eleven, distance 49", p. 110. A few degrees north of the naked eye detects a glimmering point where lies the Great Nebula in Andromeda.

This is indicated on the map by the number 116. With either of our three telescopes it is an interesting object, but of course it is advisable to use our largest gla.s.s in order to get as much light as possible. All that we can see is a long, shuttle-shaped nebulous object, having a brighter point near the center. Many stars are scattered over the field in its neighborhood, but the nebula itself, although its spectrum is peculiar in resembling that of a faint star, is evidently a gaseous or at any rate a meteoritic ma.s.s, since photographs show it to be composed of a series of imperfectly separated spirals surrounding a vast central condensation. This peculiarity of the Andromeda nebula, which is invisible with telescopes although conspicuous in the photographs, has, since its discovery a few years ago, given a great impetus to speculation concerning the transformation of nebulae into stars and star cl.u.s.ters. No one can look at a good photograph of this wonderful phenomenon without noticing its resemblance to the ideal state of things which, according to the nebular hypothesis, must once have existed in the solar system. It is to be remembered, however, that there is probably sufficient material in the Andromeda nebula to make a system many times, perhaps hundreds or thousands of times, as extensive as that of which our sun is the center. If one contemplates this nebula only long enough to get a clear perception of the fact that creation was not ended when, according to the Mosaic history, G.o.d, having in six days finished "the heavens and the earth and all the host of them," rested from all his work, a good blow will have been dealt for the cause of truth. Systems far vaster than ours are now in the bud, and long before they have bloomed, ambitious man, who once dreamed that all these things were created to serve him, will probably have vanished with the extinguishment of the little star whose radiant energy made his life and his achievements briefly possible.

[4] For further details on this subject see Astronomy with an Opera-gla.s.s.

In August, 1885, a new star of magnitude six and a half made its appearance suddenly near the center of the Andromeda nebula. Within one year it had disappeared, having gradually dwindled until the great Was.h.i.+ngton telescope, then the largest in use, no longer showed it. That this was a phenomenon connected with the nebula is most probable, but just what occurred to produce it n.o.body knows. The observed appearances might have been produced by a collision, and no better hypothesis has yet been suggested to account for them.

Near the opposite end of the constellation from alpha we find the most interesting of triple stars in gamma. The two larger components of this beautiful star are of magnitudes three and six, distance 10", colors golden yellow and deep blue. The three-inch shows them finely. The smaller star is itself double, its companion being of magnitude eight, distance when discovered in 1842 0.5", color bluish green. A few years ago this third star got so close to its primary that it was invisible even with the highest powers of the great Lick telescope, but at present it is widening again. In October, 1893, I had the pleasure of looking at gamma Andromedae with the Lick telescope, and at that time it was possible just to separate the third star. The angle seemed too small for certain measurement, but a single setting of the micrometer by Mr.

Barnard, to whose kindness I was indebted for my view of the star, gave 0.17" as the approximate distance. In 1900 the distance had increased to 0.4", p. 115. The brilliance of color contrast between the two larger stars of gamma Andromedae is hardly inferior to that exhibited in beta Cygni, so that this star may be regarded as one of the most picturesque of stellar objects for small telescopes.

Other pleasing objects in this constellation are the binary star 36, magnitudes six and six and a half, distance 1", p. 17--the two stars are slowly closing and the five-inch gla.s.s is required to separate them: the richly colored variable R, which fades from magnitude five and a half to invisibility, and then recovers its light in a period of about four hundred and five days; and the bright star cl.u.s.ter 457, which covers a s.p.a.ce about equal to the area of the full moon.

Just south of the eastern end of Andromeda is the small constellation Triangulum, or the Triangles, containing two interesting objects. One of these is the beautiful little double 6, magnitudes five and six, distance 3.8", p. 77, colors yellow and blue; and the other, the nebula 352, which equals in extent the star cl.u.s.ter in Andromeda described above, but nevertheless appears very faint with our largest gla.s.s. Its faintness, however, is not an indication of insignificance, for to very powerful telescopes it exhibits a wonderful system of nuclei and spirals--another bit of chaos that is yielding by age-long steps to the influence of demiurgic forces.

A richer constellation than Andromeda, both for naked-eye and telescopic observation, is Perseus, which is especially remarkable for its star cl.u.s.ters. Two of these, 512 and 521, const.i.tute the celebrated double cl.u.s.ter, sometimes called the Sword-hand of Perseus, and also chi Persei. To the smallest telescope this aggregation of stars, ranging in magnitude from six and a half to fourteen, and grouped about two neighboring centers, presents a marvelous appearance. As an educative object for those unaccustomed to celestial observations it may be compared among star cl.u.s.ters to beta Cygni among double stars, for the most indifferent spectator is struck with wonder in viewing it. All the other cl.u.s.ters in Perseus represented on the map are worth examining, although none of them calls for special mention, except perhaps 584, where we may distinguish at least a hundred separate stars within an area less than one quarter as expansive as the face of the moon.

Among the double stars of Perseus we note first eta, whose components are of magnitudes four and eight, distance 28", colors white and pale blue. The double epsilon is especially interesting on account of an alleged change of color from blue to red which the smaller star undergoes coincidently with a variation of brightness. The magnitudes are three and eight, distance 9", p. 9. An interesting multiple is zeta, two of whose stars at least we can see. The magnitudes are three, nine, ten, and ten, distances 13", p. 207, 90", and 112".

The chief attraction in Perseus is the changeful and wonderful beta, or Algol, the great typical star among the short-period variables. During the greater part of its period this star is of magnitude two and two tenths, but for a very short time, following a rapid loss of light, it remains at magnitude three and seven tenths. The difference, one magnitude and a half, corresponds to an actual difference in brightness in the ratio of 3.75 to 1. The entire loss of light during the declension occupies only four hours and a half. The star remains at its faintest for a few minutes only before a perceptible gain of light occurs, and the return to maximum is as rapid as was the preceding decline. The period from one minimum to the next is two days twenty hours forty-eight minutes fifty-three seconds, with an irregularity amounting to a few seconds in a year. The Arabs named the star Algol, or the Demon, on account of its eccentricity which did not escape their attention; and when Goodricke, in 1782, applied a scientific method of observation to it, the real cause of its variations was suggested by him, but his explanation failed of general acceptance until its truth was established by Prof. E. C. Pickering in 1880. This explanation gives us a wonderful insight into stellar const.i.tution. According to it, Algol possesses a companion as large as the sun, but invisible, both because of its proximity to that star and because it yields no light, and revolving in a plane horizontal to our line of sight. The period of revolution is identical with the period of Algol's cycle of variation, and the diminution of light is caused by the interposition of the dark body as it sweeps along that part of its...o...b..t lying between our point of view and the disk of Algol. In other words, once in every two days twenty hours and forty-nine minutes Algol, as seen from the earth, undergoes a partial eclipse.

In consequence of the great comparative ma.s.s of its dark companion, Algol itself moves in an orbit around their common center with a velocity quite sufficient to be detected by the s.h.i.+fting of the lines in its spectrum. By means of data thus obtained the ma.s.s, size, and distance apart of Algol and its singular comrade have been inferred. The diameter of Algol is believed to be about 1,125,000 miles, that of the dark body about 840,000 miles, and the mean distance from center to center 3,230,000 miles. The density of both the light and the dark star is slight compared with that of the sun, so that their combined ma.s.s is only two thirds as great as the sun's.

Mention has been made of a slight irregularity in Algol's period of variation. Basing his calculations upon this inequality, Dr. Chandler has put forward the hypothesis that there is another invisible body connected with Algol, and situated at a distance from it of about 1,800,000,000 miles, and that around this body, which is far more ma.s.sive than the others, Algol and its companions revolve in a period of one hundred and thirty years! Dr. Chandler has earned the right to have his hypotheses regarded with respect, even when they are as extraordinary as that which has just been described. It needs no indulgence of the imagination to lend interest to Algol; the simple facts are sufficient. How did that bright star fall in with its black neighbors? Or were they created together?

[Ill.u.s.tration: MAP NO. 25.]

Pa.s.sing to the region covered by map No. 25, our eyes are caught by the curious figure, formed by the five brightest stars of the constellation Ca.s.siopeia, somewhat resembling the letter W. Like Perseus, this is a rich constellation, both in star cl.u.s.ters and double stars. Among the latter we select as our first example sigma, in which we find a combination of color that is at once very unusual and very striking--green and blue. The magnitudes are five and seven, distance 3", p. 324. Another beautiful colored double is eta, whose magnitudes are four and seven and a half, distance 5", p. 200, colors white and purple. This is one of the comparatively small number of stars the measure of whose distance has been attempted, and a keen sense of the uncertainty of such measures is conveyed by the fact that authorities of apparently equal weight place eta Ca.s.siopeiae at such discordant distances as 124,000,000,000,000 miles, 70,000,000,000,000 miles, and 42,000,000,000,000 miles. It will be observed that the difference between the greatest and the least of these estimates is about double the entire distance given by the latter. The same thing is practically true of the various attempts to ascertain the distance of the other stars which have a perceptible parallax, even those which are evidently the nearest. In some cases the later measures increase the distance, in other cases they diminish it; in no case is there anything like a complete accord. Yet of course we are not to infer that it is hopeless to learn anything about the distances of the stars. With all their uncertainties and disagreements the few parallaxes we possess have laid a good foundation for a knowledge of the dimensions of at least the nearer parts of the universe.

We find an interesting triple in psi, the magnitudes of the larger components being four and a half and eight and a half, distance 30". The smaller star has a nine-and-a-half-magnitude companion, distance 3". A more beautiful triple is iota, magnitudes four, seven, and eight, distances 2", p. 256, and 7.5", p. 112. Ca.s.siopeia contains many star cl.u.s.ters, three of which are indicated in the map. Of these 392 is perhaps the most interesting, as it includes stars of many magnitudes, among which are a red one of the eighth magnitude, and a ninth-magnitude double whose components are 8" apart. Not far from the star kappa we find the spot where the most brilliant temporary star on record made its appearance on November 11, 1572. Tycho Brahe studied this phenomenon during the entire period of its visibility, which lasted until March, 1574. It burst out suddenly with overpowering splendor, far outs.h.i.+ning every fixed star, and even equaling Venus at her brightest. In a very short time it began to fade, regularly diminis.h.i.+ng in brightness, and at the same time undergoing changes of color, ending in red, until it disappeared. It has never been seen since, and the suspicion once entertained that it was a variable with a period considerably exceeding three hundred years has not been confirmed. There is a tenth-magnitude star near the place given by Tycho as that occupied by the stranger.

Many other faint stars are scattered about, however, and Tycho's measures were not sufficiently exact to enable us to identify the precise position of his star. If the phenomenon was due to a collision, no reappearance of the star is to be expected.

Camelopardalus is a very inconspicuous constellation, yet it furnishes considerable occupation for the telescope. Sigma 390, of magnitude five, has a companion of magnitude nine and a half, distance 15", 160. Sigma 385, also of the fifth magnitude, has a ninth-magnitude companion, distance only 2.4", p. 160. According to some observers, the larger star is yellow and the smaller white. The star 1 is a very pretty double, magnitudes both six, distance 10.4". Its neighbor 2 of magnitude six has an eighth-magnitude companion, distance 1.7", p. 278. The star 7 of magnitude five is also double, the companion of magnitude eight being distant only 1.2". A glance at star cl.u.s.ter 940, which shows a slight central condensation, completes our work in Camelopardalus, and we turn to Ursa Major, represented in map No. 26. Here there are many interesting doubles and triples. Beginning with iota we find at once occupation for our largest gla.s.s. The magnitudes are three and ten, distance 10", p. 357. In the double star 23 the magnitudes are four and nine, distance 23", p. 272. A more pleasing object is sigma^2, a greenish fifth-magnitude star which has an eighth-magnitude companion, distance 2.6", p. 245. A good double for our four-inch gla.s.s is xi, whose magnitudes are four and five, distance 1.87", p. 183. This is a binary with a period of revolution of about sixty years, and is interesting as the first binary star whose orbit was determined. Savary calculated it in 1828. Near by is nu, a difficult double, magnitudes four and ten and a half, distance 7", p. 147. In 57 we find again an easy double magnitudes six and eight, distance 5.5", p. 4. Another similar double is 65, magnitudes six and eight, distance 3.9", p. 38. A third star, magnitude seven, is seen at a distance of 114" from the primary.

We come now to Ursa Major's princ.i.p.al attraction zeta, frequently called Mizar. The naked eye perceives near it a smaller star, named Alcor. With the three-inch gla.s.s and a medium power we divide Mizar into two bright stars brilliantly contrasted in color, the larger being white and the smaller blue-green. Beside Alcor, several fainter stars are seen scattered over the field of view, and, taken all in all, there are very few equally beautiful sights in the starry heavens. The magnitudes of the double are three and four, distance 14.5", p. 148. The large star is again double, although no telescope has been able to show it so, its duplicity being revealed, like that of beta Aurigae, by the periodical splitting of the lines in its spectrum.

Ursa Major contains several nebulae which may be glimpsed with telescopes of moderate dimensions. An interesting pair of these objects, both of which are included in one field of view, is formed by 1949 and 1950. The first named is the brighter of the two, its nucleus resembling a faint star. The nebula 2343 presents itself to us in the form of a faint, hazy star, but with large telescopes its appearance is very singular.

According to a picture made by Lord Rosse, it bears no little resemblance to a skull, there being two symmetrically placed holes in it, each of which contains a star.

[Ill.u.s.tration: MAP NO. 26.]

The portion of Canes Venatici, represented in map No. 26, contains two or three remarkable objects. Sigma 1606 is a close double, magnitudes six and seven, distance 1", p. 336. It is a pretty sight with the five-inch. The double star 2 is singular in that its larger component is red and its smaller blue; magnitudes six and eight, distance 11.4", p.

260. Still more beautiful is 12, commonly called Cor Caroli. This double is wide, and requires but a slight magnifying power. The magnitudes are three and six, distance 20", colors white or light yellow and blue. The nebula 3572, although we can see it only as a pair of misty specks, is in reality a very wonderful object. Lord Rosse's telescope has revealed in it a complicated spiral structure, recalling the photographs of the Andromeda nebula, and indicating that stupendous changes must be in process within it, although our records of observation are necessarily too brief to bring out any perceptible alteration of figure. It would seem that the astronomer has, of all men, the best reasons for complaining of the brevity of human life.

Lastly, we turn to Ursa Minor and the Pole Star. The latter is a celebrated double, not difficult, except with a telescope of less than three inches aperture in the hands of an inexperienced observer. The magnitudes are two and nine, distance 18.5". The small star has a dull blue color. In 1899 it was discovered by spectroscopic evidence that the Pole Star is triple. In pi' we see a wide double, magnitudes six and seven, distance 30", p. 83.

This completes our survey of the starry heavens.

CHAPTER VIII

SCENES ON THE PLANETS

"These starry globes far surpa.s.sed the earth in grandeur, and the latter looked so diminutive that our empire, which appeared only as a point on its surface, awoke my pity."--CICERO, THE DREAM OF SCIPIO.

Although amateurs have played a conspicuous part in telescopic discovery among the heavenly bodies, yet every owner of a small telescope should not expect to attach his name to a star. But he certainly can do something perhaps more useful to himself and his friends; he can follow the discoveries that others, with better appliances and opportunities, have made, and can thus impart to those discoveries that sense of reality which only comes from seeing things with one's own eyes. There are hundreds of things continually referred to in books and writings on astronomy which have but a misty and uncertain significance for the mere reader, but which he can easily verify for himself with the aid of a telescope of four or five inches aperture, and which, when actually confronted by the senses, a.s.sume a meaning, a beauty, and an importance that would otherwise entirely have escaped him. Henceforth every allusion to the objects he has seen is eloquent with intelligence and suggestion.

Take, for instance, the planets that have been the subject of so many observations and speculations of late years--Mars, Jupiter, Saturn, Venus. For the ordinary reader much that is said about them makes very little impression upon his mind, and is almost unintelligible. He reads of the "snow patches" on Mars, but unless he has actually seen the whitened poles of that planet he can form no clear image in his mind of what is meant. So the "belts of Jupiter" is a confusing and misleading phrase for almost everybody except the astronomer, and the rings of Saturn are beyond comprehension unless they have actually been seen.

It is true that pictures and photographs partially supply the place of observation, but by no means so successfully as many imagine. The most realistic drawings and the sharpest photographs in astronomy are those of the moon, yet I think n.o.body would maintain that any picture in existence is capable of imparting a really satisfactory visual impression of the appearance of the lunar globe. n.o.body who has not seen the moon with a telescope--it need not be a large one--can form a correct and definite idea of what the moon is like.

The satisfaction of viewing with one's own eyes some of the things the astronomers write and talk about is very great, and the illumination that comes from such viewing is equally great. Just as in foreign travel the actual seeing of a famous city, a great gallery filled with masterpieces, or a battlefield where decisive issues have been fought out illuminates, for the traveler's mind, the events of history, the criticisms of artists, and the occurrences of contemporary life in foreign lands, so an acquaintance with the sights of the heavens gives a grasp on astronomical problems that can not be acquired in any other way. The person who has been in Rome, though he may be no archaeologist, gets a far more vivid conception of a new discovery in the Forum than does the reader who has never seen the city of the Seven Hills; and the amateur who has looked at Jupiter with a telescope, though he may be no astronomer, finds that the announcement of some change among the wonderful belts of that cloudy planet has for him a meaning and an interest in which the ordinary reader can not share.

[Ill.u.s.tration: JUPITER SEEN WITH A FIVE-INCH TELESCOPE.

Shadow of a satellite visible.]

Jupiter is perhaps the easiest of all the planets for the amateur observer. A three-inch telescope gives beautiful views of the great planet, although a four-inch or a five-inch is of course better. But there is no necessity for going beyond six inches' aperture in any case.

For myself, I should care for nothing better than my Byrne five-inch of fifty-two inches' focal distance. With such a gla.s.s more details are visible in the dark belts and along the bright equatorial girdle than can be correctly represented in a sketch before the rotation of the planet has altered their aspect, while the shadows of the satellites thrown upon the broad disk, and the satellites themselves when in transit, can be seen sometimes with exquisite clearness. The contrasting colors of various parts of the disk are also easily studied with a gla.s.s of four or five inches' aperture.

There is a charm about the great planet when he rides high in a clear evening sky, lording it over the fixed stars with his serene, unflickering luminousness, which no possessor of a telescope can resist.

You turn the gla.s.s upon him and he floats into the field of view, with his _cortege_ of satellites, like a yellow-and-red moon, attended by four miniatures of itself. You instantly comprehend Jupiter's mastery over his satellites--their allegiance is evident. No one would for an instant mistake them for stars accidentally seen in the same field of view. Although it requires a very large telescope to magnify their disks to measurable dimensions, yet the smallest gla.s.s differentiates them at once from the fixed stars. There is something almost startling in their appearance of companions.h.i.+p with the huge planet--this sudden verification to your eyes of the laws of gravitation and of central forces. It is easy, while looking at Jupiter amid his family, to understand the consternation of the churchmen when Galileo's telescope revealed that miniature of the solar system, and it is gratifying to gaze upon one of the first battle grounds whereon science gained a decisive victory for truth.

The swift changing of place among the satellites, as well as the rapidity of Jupiter's axial rotation, give the attraction of visible movement to the Jovian spectacle. The planet rotates in four or five minutes less than ten hours--in other words, it makes two turns and four tenths of a third turn while the earth is rolling once upon its axis. A point on Jupiter's equator moves about twenty-seven thousand miles, or considerably more than the entire circ.u.mference of the earth, in a single hour. The effect of this motion is clearly perceptible to the observer with a telescope on account of the diversified markings and colors of the moving disk, and to watch it is one of the greatest pleasures that the telescope affords.

It would be possible, when the planet is favorably situated, to witness an entire rotation of Jupiter in the course of one night, but the beginning and end of the observation would be more or less interfered with by the effects of low alt.i.tude, to say nothing of the tedium of so long a vigil. But by looking at the planet for an hour at a time in the course of a few nights every side of it will have been presented to view. Suppose the first observation is made between nine and ten o'clock on any night which may have been selected. Then on the following night between ten and eleven o'clock Jupiter will have made two and a half turns upon his axis, and the side diametrically opposite to that seen on the first night will be visible. On the third night between eleven and twelve o'clock Jupiter will have performed five complete rotations, and the side originally viewed will be visible again.

Owing to the rotundity of the planet, only the central part of the disk is sharply defined, and markings which can be easily seen when centrally located become indistinct or disappear altogether when near the limb.

Approach to the edge of the disk also causes a foreshortening which sometimes entirely alters the aspect of a marking. It is advisable, therefore, to confine the attention mainly to the middle of the disk. As time pa.s.ses, clearly defined markings on or between the cloudy belts will be seen to approach the western edge of the disk, gradually losing their distinctness and altering their appearance, while from the region of indistinct definition near the eastern edge other markings slowly emerge and advance toward the center, becoming sharper in outline and more clearly defined in color as they swing into view.

Watching these changes, the observer is carried away by the reflection that he actually sees the turning of another distant world upon its axis of rotation, just as he might view the revolving earth from a standpoint on the moon. Belts of reddish clouds, many thousands of miles across, are stretched along on each side of the equator of the great planet he is watching; the equatorial belt itself, brilliantly lemon-hued, or sometimes ruddy, is diversified with white globular and balloon-shaped ma.s.ses, which almost recall the appearance of summer cloud domes hanging over a terrestrial landscape, while toward the poles shadowy expanses of gradually deepening blue or blue-gray suggest the comparative coolness of those regions which lie always under a low sun.

[Ill.u.s.tration: ECLIPSES AND TRANSITS OF JUPITER'S SATELLITES.

Satellite I and the shadow of III are seen in transit. IV is about to be eclipsed.]