Popular Science Monthly/Volume 31/June 1887/Astronomy with an Opera-Glass II
|ASTRONOMY WITH AN OPERA-GLASS.|
THE STARS OF SUMMER.
A SINGULAR proof of popular ignorance of the starry heavens, as well as of popular curiosity concerning any uncommon celestial phenomenon, is furnished by the curious notions prevailing about the planet Venus. When Venus began to attract general attention in the western sky in the early evening some two months ago, speculation quickly became rife about it, particularly on the great Brooklyn Bridge. As the planet hung dazzlingly bright over the New Jersey horizon, some people appeared to think it was the light of Liberty's torch, mistaking the bronze goddess's real flambeau for a part of the electric-light system of the metropolis. Finally (to judge from the letters written to the newspapers, and the questions asked of individuals supposed to know something about the secrets of the sky), the conviction seems to have become pretty widely distributed that the strange light in the west was no less than an electrically illuminated balloon, nightly sent skyward by Mr. Edison, for no other conceivable reason than a wizardly desire to mystify his fellow-men. I have positive information that this ridiculous notion has been actually entertained by more than one person of intelligence. And it is not improbable, that as Venus glows with increasing splendor in the serene evenings of June, she will continue to be mistaken for some petty artificial light instead of the magnificent world that she is, sparkling out there in the sunshine like a globe of burnished silver. Yet Venus as an evening star is not so rare a phenomenon that people of intelligence should be surprised at it. Once in every 584 days she reappears in the sunset sky—
"Gem of the crimson-colored even,
Companion of retiring day."
No eye can fail to note her, and as the nearest and most beautiful of the Earth's sisters it would seem that everybody should be as familiar with her appearance as with the face of a friend. But the popular ignorance of Venus, and the other members of the planetary family to which our mother, the Earth, belongs, is only an index of the denser ignorance concerning the stars—the brothers of our great father, the Sun. I believe this ignorance is largely due to mere indifference, which, in its turn, arises from a false and pedantic method of presenting astronomy as a jumble of mathematical formulæ, and a humble handmaiden of the art of navigation. Some teachers of astronomy are so fearful that their imagination may run away with them in the boundless fields of the universe, that they hobble it with a chain of ephemerides, break its jaw with a logarithmic bit, and end by earning what they, perhaps unconsciously, seek, a niche in the temple of Dry-as-dust. Of course, the public looks upon such things with indifference. Understand, I do not mean to cast doubt upon the scientific value of technical work in astronomy. The science could not exist without it. And no reproach is intended to those who have made the spectroscope reveal the composition of the sun and stars, and who are now making photography picture the heavens as they are, and even reveal phenomena which lie beyond the range of human vision. These are the men who have taken astronomy out of its swaddling-clothes, and set it on its feet as a progressive science. But when one sees the depressing and repellent effect that has evidently been produced upon the popular mind by the ordinary methods of presenting astronomy, one can not resist the temptation to utter a vigorous protest, and to declare that this glorious science is not the grinning mathematical skeleton that it has been represented to be.
Whoever will use an opera-glass, or even his naked eyes, with intelligence, in surveying the heavens, will quickly convince himself that all of astronomy is not embraced in the "Nautical Almanac."
In the April number of "The Popular Science Monthly" I pointed out some of the most interesting objects to be seen among the stars that adorn the sky in spring. The annual revolution of the heavens has now carried those stars that in April shone in the western sky below the horizon, while the constellations that were then in the east have now climbed to the zenith, or passed over to the west, and a fresh set of stars has taken their place in the east. In the present article we shall deal with what may be called the stars of summer; and, in order to furnish occupation for the observer with an opera-glass throughout the summer months, I have endeavored to so choose the constellations in which our explorations will be made, that some of them shall be favorably situated in each of the months of June, July, and August. The circular map represents the heavens at midnight on the 1st of June; at eleven o'clock, on the 15th of June; at ten o'clock, on the 1st of July; at nine o'clock, on the 15th of July; and at eight o'clock, on the 1st of August. Remembering that the center of the map is the point over his head, and that the edge of it represents the circle of the horizon, the reader, by a little attention and comparison with the sky, will be able to fix in his mind the relative situation of the
various constellations. The maps that follow will show him these constellations on a larger scale, and give him the names of their chief stars.
The observer need not wait until midnight on the 1st of June in order to find some of the constellations included in our map. Earlier in the evening, at about that date, say at nine o'clock, he will be able to see many of these constellations, but he must look for them farther toward the east than they are represented in the map. The bright stars in Boötes and Virgo, for instance, instead of being over in the southwest, as in the map, will be near the meridian; while Lyra, instead of shining high overhead, will be found climbing up out of the northeast. It would be well to begin at nine o'clock, about the 1st of June, and watch the motion of the heavens for two or three hours. At the commencement of the observations you will find the stars in Boötes, Virgo, and Lyra in the positions I have just mentioned, while half-way down the western sky will be seen the Sickle of Leo (see "Popular Science Monthly" for April). The brilliant Procyon and Capella will be found almost ready to set in the west and northwest, respectively. Between Procyon and Capella, and higher above the horizon, shine the twin stars in Gemini, with the planets Venus and Saturn, near each other, below them. There will be no difficulty in recognizing Venus, for it is now brighter than any other star in the heavens. Saturn would be regarded also as a very bright star, but for the overpowering contrast with its more brilliant sister. Looking over into the south, the observer will see the planet Jupiter a little east of Spica in Virgo, and second only to Venus in brilliancy.
In an hour Saturn and Venus will be setting, and Jupiter will be well past the meridian. In another hour the observer will perceive that the constellations are approaching the places given to them in our map, and at midnight he will find them all in their assigned positions. A single evening spent in observations of this sort will teach him more about the places of the stars than he could learn from a dozen books.
Taking, now, the largest opera-glass you can get (I have before said that the diameter of the object-glasses should not be less than 1·5 inch, and, I may add, the larger they are the better), find the constellation Scorpio, and its chief star Antares. The map shows you where to look for it at midnight on the 1st of June. If you prefer to begin at nine o'clock at that date, then, instead of looking directly in the south for Scorpio, you must expect to see it just rising in the southeast. You will recognize Antares by its fiery color, as well as by the striking arrangement of its surrounding stars. There are few constellations which bear so close a resemblance to the objects they are named after as Scorpio. It does not require a very violent exercise of the imagination to see in this long, winding trail of stars a gigantic scorpion, with its head to the west, and flourishing its upraised sting that glitters with a pair of twin stars, as if ready to strike. Readers of the old story of Phaeton's disastrous attempt to drive the chariot of the Sun for a day will remember it was the sight of this threatening monster that so terrified the ambitious youth that he lost control of Apollo's horses, and came near burning the earth up by running the Sun into it.
Antares rather gains in redness when viewed with a glass. Its color is very remarkable, and it is a curious circumstance that with powerful telescopes a small, bright-green star is seen apparently almost touching it. Antares belongs to Secchi's third type of suns, that in which the spectroscopic appearances suggest the existence of a powerful absorptive atmosphere, and which are believed on various grounds to be, as Lockyer has said, "in the last visible stage of cooling"; in other words, almost extinct. This great, red star probably in actual size exceeds our sun, and no one can help feeling the sublime nature of those studies which give us reason to think that here we can
actually behold almost the expiring throes of a giant brother of our giant Sun. Only, the lifetime of a sun is many millions of years, and its gradual extinction, even after it has reached a stage as advanced as that of Antares is supposed to be, may occupy a longer time than the whole duration of the human race.
The opera-glass will show a number of faint stars scattered around Antares. Turn now to Beta (ß) in Scorpio, with the glass. A very pretty pair of stars will be seen hanging below ß. Sweeping down, ward from this point to the horizon you will find many beautiful star-fields. The star marked Nu (ν) is a double which you will be able to separate with a powerful field-glass, the distance between its components being 40".
And next let us look at a star-cluster. You will see on the map an object marked 4 M., near Antares. Its designation means that it is No. 4 in Messier's catalogue of nebulæ. It is not a true nebula, but a closely compacted cluster of stars. With the opera-glass, if you are looking in a clear and moonless night, you will see it as a curious nebulous speck. With a field-glass its real nature is more apparent, and it is seen to blaze brighter toward the center. It is, in fact, one of those universes within the universe where thousands of suns are associated together by some unknown law of aggregation into assemblages of whose splendor the slight view that we can get gives us but the faintest conception.
The object above and to the left of Antares, marked in the map 80 M., is a nebula, and although the nebula itself is too small to be seen with an opera-glass (a field-glass shows it as a mere wisp of light), yet there is a pretty array of small stars in its neighborhood worth looking at. Besides, this nebula is of special interest, because in 1860 a star suddenly took its place. At least, that is what seemed to have happened. What really did occur, probably, was that a variable or temporary star, situated between us and the nebula, and ordinarily too faint to be perceived, received a sudden and enormous accession of light, and blazed up so brightly as to blot out of sight the faint nebula behind it. If this star should make its appearance again, it could easily be seen with an opera-glass, and so it will not be useless for the reader to know where to look for it. The quarter of the heavens with which we are now dealing is famous for these celestial conflagrations, if so they may be called.
We shall presently see some examples of star-clusters and nebulæ with which the instruments we are using are better capable of dealing. In the mean time, let us follow the bending row of stars from Antares toward the south and east. When you reach the star Mu (µ), you are not unlikely to stop with an exclamation of admiration, for the glass will separate it into two stars that, shining side by side, seem trying to rival each other in brightness. But the next star below µ, marked Zeta (ζ), is even more beautiful. It also separates into two stars, one being reddish and the other bluish in color. The contrast in a clear night is very pleasing. But this is not all. Above the two stars you will notice a curious nebulous speck. Now, if you have a powerful field-glass, here is an opportunity to view one of the prettiest sights in the heavens. The field-glass not only makes the two stars appear brighter, and their colors more pronounced, but it shows a third, fainter star below them, making a small triangle, and brings other still fainter stars into sight, while the nebulous speck above turns into a charmingly beautiful little star-cluster, whose components Zeta Scorpionis. are so close that their rays are inextricably mingled in a maze of light. This little cut is an attempt to represent the scene, but no engraving can reproduce the life and sparkle of it.
Following the bend of the Scorpion's tail upward, we come to the pair of stars in the sting. These, of course, are thrown wide apart by the opera-glass. Then let us sweep off to the eastward a little way and find the cluster known as 7 M. You will see it marked on the map. Above it, and near enough to be included in the same field of view, is 6 M., a smaller cluster. Both of these have a sparkling appearance with an opera-glass, and by close attention some of the separate stars in 7 M. may be detected. With a field-glass these clusters become much more striking and starry looking, and the curious radiated structure of 7 M. comes out.
In looking at such objects we can not too often recall to our minds the significance of what we see—that these glimmering specks are the lights in the windows of the universe which carry to us, across inconceivable tracts of space, the assurance that we and our little system are not alone in the heavens; that all around us, and even on the very confines of immensity, Nature is busy, as she is here, and the laws of light, heat, gravitation (and why not of life?) are in full activity.
The clusters we have just been looking at lie on the borders of Scorpio and Sagittarius. Let us cross over into the latter constellation, which commemorates the centaur Chiron. We are now in another, and even a richer, region of wonders. The Milky-Way, streaming down out of the northeast, pours, in a luminous flood through Sagittarius, inundating that whole region of the heavens with seeming deeps and shallows, and finally bursting the barriers of the horizon disappears, only to glow with redoubled splendor in the southern hemisphere. The stars Zeta (ζ), Tau (τ), Sigma (σ), Phi (φ), Lambda (λ), and Mu (μ) indicate the outlines of a figure sometimes called the Milk-Dipper, which is very evident when the eye has once recognized it. On either side of the upturned handle of this dipper-like figure lie some of the most interesting objects in the sky. Let us take the star μ for a starting-point. Sweep downward and to the right a little way, and you will be startled by a most singular phenomenon that has suddenly made its appearance in the field of view of your glass. You may, perhaps, be tempted to congratulate yourself on having got ahead of all the astronomers, and discovered a comet. It is really a combination of a star-cluster with a nebula, and is known as 8 M. Sir John Herschel has described the "nebulous folds and masses" and dark oval gaps which he saw in this nebula with his large telescope at the Cape of Good Hope. But no telescope is needed to make it appear a wonderful object; an opera-glass suffices for that, and a field-glass reveals still more of its marvelous structure.
On the opposite side of the star μ—that is to say, above and a little to the left—is an entirely different but almost equally attractive spectacle, the swarm of stars called 24 M. Here, again, the field-glass easily shows its superiority over the opera-glass, for magnifying power is needed to bring out the innumerable little twinklers of which the cluster is composed. But, whether you use an opera-glass or a field-glass, do not fail to gaze long and steadily at this island of stars, for much of its beauty becomes evident only after the eye has accustomed itself to disentangle the glimmering rays with which the whole field of view is filled. Try the method of averted vision, and hundreds of the finest conceivable points of light will seem to spring into view out of the depths of the sky. The necessity of a perfectly clear night, and the absence of moonlight, can not be too much insisted upon for observations such as these. Everybody knows how the moonlight blots out the smaller stars. A slight haziness, or smoke, in the air produces a similar effect. It is as important to the observer with an opera-glass to have a transparent atmosphere as it is to one who would use a telescope; but, fortunately, the work of the former is not so much interfered with by currents of air. Always avoid the neighborhood of any bright light. Electric lights in particular are an abomination to star-gazers.
The cloud of stars we have just been looking at is in a very rich region of the Milky-Way, in the little modern constellation called "Sobieski's Shield," which we have not placed upon our map. Sweeping slowly upward from 24 M. a little way with the field-glass, we will pass in succession over three nebulous-looking spots. The second of these, counting upward, is the famous Horseshoe nebula. Its wonders are beyond the reach of our instrument, but its place may be recognized. Look carefully all around this region, and you will perceive that the old gods, who traveled this road (the Milky-Way was sometimes called the pathway of the gods), trod upon golden sands. Off a little way to the east you will find the rich cluster called 25 M. But do not imagine the thousands of stars that your opera-glass or field-glass reveals comprise all the riches of this Golconda of the heavens. You might ply the powers of the greatest telescope in a vain attempt to exhaust its wealth. As a hint of the wonders that lie hidden here, let me quote Father Secchi's description of a starry spot in this same neighborhood, viewed with the great telescope at Rome. After telling of "beds of stars superposed upon one another," and of the wonderful geometrical arrangement of the larger stars visible in the field, he adds:
"The greater number are arranged in spiral arcs, in which one can count as many as ten or twelve stars of the ninth to the tenth magnitude following one another in a curve, like beads upon a string. Sometimes they form rays which seem to diverge from a common focus, and, what is very singular, one usually finds, either at the center of the rays, or at the beginning of the curve, a more brilliant star of a red color, which seems to lead the march. It is impossible to believe that such an arrangement can be accidental."
The reader will recall the somewhat similar description that Admiral Smyth and Mr. Webb have given of a star-cluster in Gemini (see "Popular Science Monthly" for April).
The groups of stars forming the eastern half of the constellation of Sagittarius are worth sweeping over with the glass, as a number of pretty pairs may be found there.
Next let us pass to the double constellation adjoining Scorpio and Sagittarius on the north—Ophiuchus and the Serpent. These constellations, as our map shows, are curiously intermixed. The imagination of the old star-gazers, who named them, saw here the figure of a giant grasping a writhing serpent with his hands. The head of the serpent is under the Northern Crown, and its tail ends over the star-gemmed region that we have just described, called "Sobieski's Shield." Ophiuchus stands, as figured in Flamsteed's "Atlas," upon the back of the Scorpion, holding the serpent with one hand below the neck, this hand being indicated by the pair of stars marked Epsilon (ε) and Delta (δ), and with the other near the tail. The stars Tau (τ) and Nu (ν) indicate
the second hand. The giant's face is toward the observer, and the star Alpha (α), also called Ras Alhague, shines in his forehead, while Beta (β) and Gamma (γ) mark his right shoulder. Ophiuchus has been held to represent the famous physician Æsculapius. One may well repress the tendency to smile at these fanciful legends when he reflects upon their antiquity. There is no doubt that this double constellation is at least three thousand years old—that is to say, for thirty centuries the imagination of men has continued to shape these stars into the figures of a gigantic man struggling with a huge serpent. If it possesses no other interest, then it at least has that which attaches to all things ancient. Like many other of the constellations it has proved longer-lived than the mightiest nations. While Greece flourished and decayed, while Rome rose and fell, while the scepter of civilization has passed from race to race, these starry creations of fancy have shone on unchanged. The mind that would ignore them now deserves compassion.
The reader will observe a little circle in the map, and near it the figures 1604. This indicates the spot where one of the most famous temporary stars on record appeared in the year 1604. At first it was far brighter than any other star in the heavens; but it quickly faded, and in a little over a year disappeared. It is particularly interesting, because Kepler—the quaintest, and not far from the greatest, figure in astronomical history—wrote a curious book about it. Some of the philosophers of the day argued that the sudden outburst of the wonderful star was caused by the chance meeting of atoms. Kepler's reply was characteristic, as well as amusing:
"I will tell those disputants, my opponents, not my own opinion, but my wife's. Yesterday, when I was weary with writing, my mind being quite dusty with considering these atoms, I was called to supper, and a salad I had asked for was set before me. 'It seems, then,' said I, aloud, 'that if pewter dishes, leaves of lettuce, grains of salt, drops of water, vinegar and oil, and slices of egg, had been flying about in the air from all eternity, it might at last happen by chance that there would come a salad.' 'Yes,' says my wife, 'but not so nice and well-dressed as this of mine is.'"
While there are no objects of special interest for the observer with an opera-glass in Ophiuchus, he will find it worth while to sweep over it for what he may pick up, and, in particular, he should look at the group of stars southeast of β and γ. These stars have been shaped into a little modern asterism called Taurus Poniatowskii, and it will be noticed that five of them mark the outlines of a letter V, resembling the well-known figure of the Hyades.
Also look at the stars in the head of Serpens, several of which form a figure like a letter X. A little west of Theta (θ), in the tail of Serpens, is a beautiful swarm of little stars, upon which a field-glass may be used with advantage. The star θ is itself a beautiful double, just within the separating power of a very powerful field-glass under favorable circumstances, the component stars being only about one third of a minute apart.
Do not fail to notice the remarkable subdivisions of the Milky-Way in this neighborhood. Its current seems divided into numerous channels and bays, interspersed with gaps that might be likened to islands, and the star θ appears to be situated upon one of these islands of the galaxy. This complicated structure of the Milky-Way extends downward to the horizon, and upward through the constellation Cygnus, and of its phenomenal appearance in that region we shall have more to say farther on.
Directly north of Ophiuchus is the constellation Hercules, interesting as occupying that part of the heavens toward which the proper motion of the sun in space is bearing the earth and its fellow planets, at the rate, probably, of not less than 160,000,000 miles in a year—a stupendous voyage through space, of whose destination we are as ignorant as the crew of a ship sailing under sealed orders, and, like whom, we must depend upon such inferences as we can draw from courses and distances, for no other information comes to us from the flag-ship of our squadron.
In the accompanying map we have represented the beautiful constellations Lyra and the Northern Crown, lying on either side of Hercules. The reader should note that the point overhead in this map is not far from the star Eta (η) in Hercules. The bottom of the map is toward the south, the right-hand side is west, and the left-hand side east. It is important to keep these directions in mind, in comparing the map with the sky. For instance, the observer must not expect to look into the south and see Hercules half-way up the sky, with Lyra a little east of it; he must look for Hercules nearly overhead, and Lyra a little east of the zenith. The same precautions are not necessary in using the maps of Scorpio, Sagittarius, and Ophiuchus, because those constellations are nearer the horizon, and so the observer does not have to imagine the map as being suspended over his head.
The name Hercules sufficiently indicates the mythological origin of the constellation, and yet the Greeks did not know it by that name, for Aratus calls it "the Phantom whose name none can tell." The Northern Crown, according to fable, was the celebrated crown of Ariadne, and Lyra was the harp of Orpheus himself.
With the aid of the map you will be able to recognize the principal stars and star-groups in Hercules, and will find many interesting combinations of stars for yourself. An object of special interest is the celebrated star-cluster 13 M. You will find it on the map between the stars Eta (η) and Zeta (ζ). While an opera-glass will only show it as a faint and minute speck, lying nearly between two little stars, it is nevertheless well worth looking for, on account of the great renown of this wonderful congregation of stars. Sir William Herschel computed the number of stars contained in it as about fourteen thousand. It is roughly spherical in shape, though there are many straggling stars around it evidently connected with the cluster. In short, it is a ball of suns. The reader should not mistake what that implies, however. These suns, though truly solar bodies, are probably very much smaller than our sun. Mr. Gore has recently computed their average diameter to be about forty-five thousand miles, and the distance separating one from another to be 9,000,000,000 miles. Adopting Mr. Gore's estimates of their size and distance, I have recently shown, in a newspaper article, that, as seen from the center of the cluster, the nearest stars would shine about fourteen hundred times as bright as Sirius, while even the farthest stars in the cluster would be much brighter than Sirius, so that a world situated there would enjoy a sort of perpetual daylight, the illumination of its nocturnal sky being, perhaps, as much as fifteen times greater than the light shed from the full moon upon the earth.
If you have a field-glass, by all means try it upon 13 M. It will give you a more satisfactory view than an opera-glass is capable of doing, and will magnify the cluster so that there can be no possibility of mistaking it for a star. Compare this compact cluster, which only a powerful telescope can partially resolve into its component stars, with 7 M. and 24 M., described above, in order to comprehend the wide variety in the structure of these aggregations of stars.
The Northern Crown, although a strikingly beautiful constellation to the naked eye, offers few attractions to the opera-glass. Let us turn, then, to Lyra. I have never been able to make up my mind which of three great stars is entitled to precedence—Vega, the leading brilliant of Lyra, Arcturus in Boötes, or Capella in Auriga. They are the three leaders of the northern firmament, but which of them should be called the chief, is very hard to say. At any rate, Vega would probably be generally regarded as the most beautiful, on account of the delicate bluish tinge in its light, especially when viewed with a glass. There is no possibility of mistaking this star on account of its surprising brilliancy. Two faint stars close to Vega on the east make a beautiful little triangle with it, and thus form a further means of recognition, if any were needed. Your opera-glass will show that the floor of heaven is powdered with stars, fine as the dust of a diamond, all around the neighborhood of Vega, and the longer you gaze the more of these diminutive twinklers you will discover.
Now direct your glass to the northernmost of the two little stars near Vega, the one marked Epsilon (ε) in the map. You will perceive that it is composed of two stars of almost equal magnitude. If you had a telescope of considerable power, you would find that each of these stars is in turn double. In other words, this wonderful star which appears single to the unassisted eye, is in reality quadruple, and there is reason to think that the four stars composing it are connected in pairs, the members of each pair revolving around their common center
while the two pairs in turn circle around a center common to all. With a field-glass you will be able to see that the other star near Vega, Zeta (ζ), is also double, the distance between its components being three quarters of a minute, while the two stars in ε are a little less than 31'. The star Beta (β) is remarkably variable in brightness. You may watch these variations, which run through a regular period of about 12 days, 213 hours, for yourself. The star will be at its minimum of brightness on June 7th and 20th; July 3d, 15th, and 28th; August 10th and 23d. Between Beta and Gamma (γ) lies the beautiful Ring nebula, but it is hopelessly beyond the reach of the optical means we are employing.
Let us turn next to the stars in the west. In consulting the accompanying map of Virgo and Boötes, the observer is supposed to face the southwest, at the hours and dates mentioned above as those to which the circular map corresponds. He will then see the bright star Spica in Virgo not far above the horizon, while Arcturus will be half-way up the sky, and the Northern Crown will be near the zenith. The planet Jupiter will be close to Spica, and will completely outshine it. In fact, during the whole summer, this fine star will be to a considerable extent robbed of its brilliance by the proximity of the great planet. The reader may find it convenient to mark the place of Jupiter on the map just to the left of Spica.
The constellation Virgo is an interesting one in mythological story. Aratus tells us that the Virgin's home was once on earth, where she bore the name of Justice and in the golden age all men obeyed her. In the silver age her visits to men became less frequent, "no longer finding the spirits of former days"; and, finally, when the brazen age came with the clangor of war:
"Justice, loathing that race of men,
Winged her flight to heaven; and fixed
Her station in that region
Where still by night is seen
The Virgin goddess near to bright Boötes."
The chief star of Virgo, Spica, is remarkable for its pure white light. To my eye there is no conspicuous star in the sky equal to it in this respect, and it gains in beauty when viewed with a glass. With the aid of the map the reader will find the celebrated binary star Gamma (γ) Virginis, although he will not be able to separate its components without a telescope. It is a curious fact that the star Epsilon (ε) in Virgo has for many ages been known as the Grape-Gatherer. It has borne this name in Greek, in Latin, in Persian, and in Arabic, the origin of the appellation undoubtedly being that it was observed to rise just before the sun in the season of the vintage. It will be observed that the stars ε, δ, γ, η, and β, mark two sides of a quadrilateral figure of which the opposite corner is indicated by Denebola in the tail of Leo. Within this quadrilateral lies the marvelous Field of the Nebulæ, a region where with adequate optical power one may find hundreds of these strange objects thronging together, a very storehouse of the germs of suns and worlds. Unfortunately, these nebulæ are far beyond the reach of an opera-glass, but it is worth while to know where this curious region is, even if we can not behold the wonders it contains. The stars Omicron (ο), Pi (π), etc., forming a little group, mark the head of Virgo.
The constellation Libra, lying between Virgo and Scorpio, does not contain much to attract our attention. Its two chief stars, α and ß, Berenice's Hair. may be readily recognized west of and above the head of Scorpio. The upper one of the two, ß, has a singular greenish tint, and the lower one, α, is a very pretty double for an opera-glass.
Just north of Virgo's head will be seen the glimmering of Berenice's Hair. This little constellation was included among those described in the article on "The Stars of Spring," but it is worth looking at again in the early summer, on moonless nights, and we give here a picture of its stars as seen with a good glass. The singular arrangement of the brighter members of the cluster at once strikes the eye.
Boötes, whose leading brilliant, Arcturus, occupies the center of our map, also possesses a curious mythical history. It was called by the Greeks the Bear-Driver, because it seems continually to chase Ursa Major, the Great Bear, in his path around the pole. The story is that Boötes was the son of the nymph Calisto, whom Juno in one of her customary fits of jealousy turned into a bear. Boötes, who had become a famous hunter, one day roused a bear from her lair, and not knowing that it was his mother, was about to kill her, when Jupiter came to the rescue and snatched them both up into the sky, where they have shone ever since. How this story remained in men's minds is shown by Lucan's reference to it when, describing Brutus's visit to Cato at night, he fixes the time by the position of these constellations in the heavens:
"'Twas when the solemn dead of night came on,
When bright Calisto, with her shining son,
Now half the circle round the pole had run."
Boötes is not specially interesting for our purposes, except for the splendor of Arcturus. This star has possessed a peculiar charm for me ever since boyhood, when, having read a description of it in an old treatise on Uranography I felt an eager desire to see it. As my search for it chanced to begin at a season when Arcturus did not rise till after a boy's bed-time, I was for a long time disappointed, and I shall never forget the start of surprise and almost of awe with which I finally caught sight of it, one spring evening, shooting its flaming rays through the boughs of an apple-orchard, like a star on fire.
When near the horizon, Arcturus has a remarkably reddish color; but, after it has attained a high elevation in the sky, it appears rather a deep yellow than red. There is a scattered cluster of small stars surrounding Arcturus, forming an admirable spectacle with an opera-glass on a clear night. To see these stars well, the glass should be slowly moved about. Many of them are hidden by the glare of Arcturus. The little group of stars near the handle of the end of the Great Dipper, or, what is the same thing, the tail of the Great Bear, marks the upraised hand of Boötes. Between Berenice's Hair and the tail of the Bear you will see a small constellation called Canes Venatici, the Hunting-Dogs. On the old star-maps Boötes is represented as holding these dogs with a leash, while they are straining in chase of the Bear. You will find some pretty groupings of stars in this constellation.
And now we will turn to the east. Our next map shows Cygnus, a constellation especially remarkable for the large and striking figure that it contains, called the Northern Cross, Aquila the Eagle, the Dolphin, and the little asterisms Sagitta and Vulpecula. In consulting the map, the observer is supposed to face toward the east. In Aquila the curious arrangement of two stars on either side of the chief star of the constellation, called Altair, at once attracts the eye. Within a circle including the two attendants of Altair you will probably be able to see with the naked eye only two or three stars in addition to the three large ones. Now turn your glass upon the same spot, and you will see eight or ten times as many stars, and with a field-glass still more can be seen. Watch the star marked Eta (η), and you will find that its light is variable, being sometimes more than twice as bright as at other times. Its changes are periodical, and occupy a little over a week.
This Eagle is fabled to have been the bird that Jupiter kept beside his throne. A constellation called Antinous, invented by Tycho Brahe, is represented on some maps as occupying the lower portion of the space given to Aquila.
The Dolphin is an interesting little constellation, and the ancients said it represented the very animal on whose back the famous musician Arion rode through the sea after his escape from the sailors who tried to murder him. But some modern has dubbed it with the less romantic name of Job's Coffin, by which it is sometimes called. It presents a very pretty sight to the opera-glass.
Cygnus, the Swan, is a constellation whose mythological history is somewhat obscure, although, as remarked above, it contains one of the most clearly marked figures to be found among the stars, the famous Northern Cross. The outlines of this cross are marked with great distinctness by the stars Alpha (α), Epsilon (ε), Gamma (γ), Delta (δ), and Beta (β), together with some fainter stars lying along the main beam of the cross between β and γ. The star β, also called Albireo, is one of the most beautiful double stars in the heavens. The components are sharply contrasted in color, the larger star being golden-yellow,
while the smaller one is a deep, rich blue. With a field-glass of 1·6-inch aperture and magnifying full six times I have sometimes been able to divide this pair, and to recognize the blue color of the smaller star. It will be found a severe test for such a glass.
About half way from Albireo to the two stars ζ and ε in Aquila, is a very curious little group consisting of six or seven stars in a straight row, with a garland of other stars hanging from the center. To see it best, take a field-glass, although an opera-glass shows it.
I have indicated the place of the celebrated star 61 Cygni in the map, because of the interest attaching to it as the nearest to us, so far as we know, of all the stars in the northern hemisphere, and with one exception the nearest star in all the heavens. Yet it is very faint, and the fact that so inconspicuous a star should be nearer than such brilliants as Vega and Arcturus shows how wide is the range of magnitude among the suns that light the universe. The actual distance of 61 Cygni is something like 650,000 times as great as the distance from the earth to the sun.
The star Omicron (ο) is very interesting with an opera-glass. The naked eye sees a little star near it. The glass throws them wide apart, and divides ο itself into two stars. Now, a field-glass, if of sufficient power, will divide the larger of these stars again into two—a fine test.
Sweep around α and γ for the splendid star-fields that abound in this neighborhood; also around the upper part of the figure of the cross. We are here in one of the richest parts of the Milky-Way. Between the stars α, γ, ε, is the strange dark gap in the galaxy called the Coal-Sack, a sort of hole in the starry heavens. Although it is not entirely empty of stars, its blackness is striking in contrast with the brilliancy of the Milky-Way in this neighborhood. The divergent streams of the great river of light in this region present a very remarkable appearance.
Finally, we come to the great dragon of the sky. In using the map of Draco and the neighboring constellations, the reader is supposed to face the north. The upper edge of the center of the map is directly over the observer's head. One of the stories told of this large constellation is that it represents a dragon that had the temerity to war against Minerva. The goddess "seized it in her hand, and hurled it, twisted as it was, into the heavens round the axis of the world, before it had time to unwind its contortions." Others say it is the dragon that guarded the golden apples in the Garden of the Hesperides, and that was slain by the redoubtable Hercules. At any rate, it is plainly a monster of the first magnitude. The stars β,γ, ξ, ν and μ represent its head, while its body runs trailing along, first sweeping in a long curve toward Cepheus, and then bending around and passing between the two bears. Try ν with your opera-glass, and if you succeed in seeing it double you may congratulate yourself on your keen sight. The distance between the stars is about 1'. Notice the contrasted colors of γ and β, the former being a rich orange and the latter white. As you sweep along the winding way that Draco follows, you will run across many striking fields of stars, although the heavens are not as rich here as in the splendid regions that we have just left. You will also find that Cepheus, although not an attractive constellation to the naked eye, is worth some attention with an opera-glass. It, however, sinks into insignificance in comparison with its neighbor Cassiopeia, but that constellation belongs rather to the autumn sky, and we shall pass it by here.
The reader will find it both interesting and instructive to watch the movements of Venus through the summer. On June 1st as we have seen, Venus will be near Saturn in the constellation Gemini. But the two planets will rapidly part company, Saturn sinking toward the horizon day by day until it is no longer seen, while Venus, moving eastwardly, rises higher every evening. About the middle of July, Venus, having reached her greatest eastern elongation, will turn upon
her track and move westwardly, setting a little earlier every night. At the middle of August she will attain her greatest brilliancy, and will be a superb phenomenon. Being then in that part of her orbit which passes between the earth and the sun, her illuminated disk will be in the form of a crescent. A good field-glass, under favorable circumstances, will show this crescent form of Venus, and a most beautiful sight it is. The crescent will grow larger and narrower in proportion as Venus approaches nearer to the line joining the earth and the sun, and, as she approaches that line, of course she will draw closer to the horizon, until about the end of August, she disappears from the evening sky, to reappear in the east as a morning-star in the autumn.
Jupiter will remain in the neighborhood of Spica in Virgo throughout the summer. The surface features of this majestic planet are far beyond the reach of an opera- or field-glass, but some of the members of his little family of four moons may occasionally be caught sight of. With an opera-glass not more than one or two of these can be seen as excessively minute dots of light half-hidden in the glare of the planet. If you succeed under favorable circumstances in seeing Jupiter and his Moons. (Seen with a field-glass; power, six diameters.) one of these moons with your glass, you will be all the more astonished to learn that there are several apparently well-authenticated instances of one of the moons of Jupiter having been seen with the naked eye.
With a field-glass, however, you will have no difficulty in seeing all of the moons when they are properly situated. If you miss one or more of them, you may know that it is either between you and the planet, or behind the planet, or buried in the planet's shadow, Or else so close to the planet as to be concealed by its radiance. For the convenience of the beginner, I will indicate the positions of Jupiter's moons for several evenings in June, based upon the "Nautical Almanac" predictions; the time of observation is supposed to be 10.30 o'clock p. m.:
On June 1st all four satellites will be visible with a good field-glass, one being on the eastern and the other three on the western side of the planet, two of the latter appearing close together like a double star.
On June 2d the satellites will all be on the western side, two of them being pretty close to the planet and also close together, while the others are more distant and wide apart.
On June 6th all four will be on the eastern side of Jupiter, and three of them, besides being near the planet, will be close together in a slanting row. It will require close watching with a fine glass to see them all, but the spectacle will be well worth some painstaking on the part of the observer.
On June 8th two will be on one side and two on the other, the two on the west being close together, while those on the east are widely separated.
On June 14th two will be close together on the east, while one is visible on the west, and the fourth, the outermost of the system, is passing just above the north pole of the planet, and so close that it will probably be beyond the ability even of a powerful field-glass to detect it.
On June 17th there will be a very good opportunity for the inexperienced observer to see all four of the satellites, as two will be on each side of the planet and all will be well separated.
On June 22d one satellite will be on the east of Jupiter, and the other three on the west, all in a bunch, and close to the planet.
Of course, since the motions of the satellites, particularly of the inner ones, are very rapid, their positions are continually changing, and their configurations are different every night. I have merely indicated their places for a few evenings, in order that the observer may be able to recognize the satellites when he sees them. If he has any doubt about his identification of them, or thinks they may be little stars, he has only to carefully note their position and then look at them again the next evening. He may even notice their motion in the course of a single evening, if he begins early and follows them for three or four hours.