IXAUGUST

July—Libra and Scorpio

With a telescope of medium size, one will find an exquisite little green companion-star close to Antares.The little companion is so close to Antares that it is difficult to find it in the glare of light from its more brilliant neighbor. Antares is one of the giant stars of the universe. In fact it is, so far as we know, the greatest of all the giants. Its diameter is more than five hundred times that of our own sun and nearly twice that of the giant star Betelgeuze in Orion. If placed at the center of the solar system its surface would lie far beyond the orbit of Mars.

Both Ophiuchus and Scorpio are crossed by the Milky Way, that broad belt of numberless faint starsthat encircles the heavens. Some of the most wonderful and beautiful regions of the Milky Way are to be found in these two constellations.

At various times in the past, there have suddenly flashed forth brilliant stars in the Milky Way which are known as "temporary stars," or "novæ." These outbursts signify that some celestial catastrophe has taken place, the nature or cause of which is not clearly understood. Some of the most brilliant of these outbursts have occurred in these two constellations. The life of a nova is very short, a matter of a few months, and it rapidly sinks into oblivion, so nothing is to be seen of some of the most brilliant of all these stars that have appeared in this region in the past. A few are still faintly visible in large telescopes.

It was one of the twelve labors of Hercules, the hero of Grecian mythology, to vanquish the dragon that guarded the golden apples in the garden of the Hesperides. Among the constellations for July we found the large group of stars that represents the hero himself, and this month we find just to the north of Hercules the head of Draco, The Dragon. The foot of the hero rests upon the dragon's head, which is outlined by a group of four fairly bright stars forming a quadrilateral or four-sided figure. The brightest star in this group passes in its daily circuit of the pole almost through the zenith of London. That is, as it crosses the meridian of London, it is almost exactly overhead. From the head of Draco, the creature's body can be traced in a long line of stars curving first eastward, then northward, toward the pole-star to a point above Hercules, where it bends sharply westward. The body of the monster lies chiefly between its head and the bowl of the Little Dipper. The tail extends in a long line of faint stars midway between the two Dippers, or the constellations of Ursa Major and Ursa Minor, the tip of the tail lying on the line connecting the Pointers of the Big Dipper with the pole-star Polaris.

Draco, as well as Ursa Major and Ursa Minor, is a circumpolar constellation in our latitude; that is, it makes its circuit of the pole without at any time dipping below the horizon in latitudes north of 40°. It is, therefore, visible at all hours of the night in mid-latitudes of the northern hemisphere, but is seen to the best advantage during the early evening hours in the summer months. There are no remarkable stars in this constellation with the exception of Alpha, which lies halfway between the bowl of the Little Dipper and Mizar, the star at the bend in the handle of the Big Dipper.

August—Draco and Lyra

About four thousand seven hundred years ago, this star was the pole-star—lying even nearer to what was then the north pole of the heavens than Polaris does to the present position of the pole. The sun and moon exert a pull on the bulging equatorial regions of the earth, which tends to draw the plane of the earth's equator down into the plane of the ecliptic. This causes the "Precession of the Equinoxes" and at the same time a slow revolution of the earth's axis of rotation about the pole of the ecliptic. The north pole of the heavens as a result describes a circle about the pole of the ecliptic of radius 23½° in a period of 25,800 years.

Each bright star that lies near the circumference of this circle becomes in turn the pole-star sometime within this period. The star Alpha, in Draco, had its turn at being pole-star some forty-seven centuries ago. Polaris is now a little over a degree from the north pole of the heavens. During the next two centuries it will continue to approach the pole until it comes within a quarter of a degree of it, when its distance from the pole will begin to increase again. About twelve thousand years hence the magnificent Vega, whose acquaintance we will now make, will be the most brilliant and beautiful of all pole-stars.

Vega (Arabic for "Falling Eagle") is the resplendent, bluish-white, first-magnitude star that lies in the constellation of Lyra, The Lyre or Harp, a small, but important, constellation just east of Hercules and a little to the southeast of the head of Draco. Vega is almostexactly equal in brightness to Arcturus, the orange-colored star in Boötes, now lying west of the meridian in the early evening hours. It is also a near neighbor of the solar system, its light taking something like forty years to travel to the earth. Vega is carried nearly through the zenith of Washington and all places in the same latitude by the apparent daily rotation of the heavens. It is a star that we have no difficulty in recognizing, owing to the presence of two nearby stars that form, with it, a small equal-sided triangle with sides only two degrees in extent. If our own sun were at the distance of Vega, it would not appear as bright as one of these faint stars, so much more brilliant is this magnificent sun than our own. The two faint stars that follow so closely after Vega and form the little triangle with it are also of particular interest. Epsilon Lyræ, which is the northern one of these two stars, may be used as a test of keen eyesight. It is the finest example in the heavens of a quadruple star—that is, "a double-double star." A keen eye can just separate this star into two without a telescope, and with the aid of a telescope, each of the two splits up into two stars, making four stars in place of the one visible to the average eye. Zeta, the other of the two stars that form the little triangle with Vega, is also a fine double star. The star that lies almost in a straight line with Epsilon and Zeta and a short distance to the south of them is a very interesting variable star known as Beta Lyræ. Its brightness changes very considerably in a period of twelve days and twenty-two hours. This change ofbrightness is due to the presence of a companion star. The two stars are in mutual revolution, and their motion is viewed at such an angle from the earth that, in each revolution, one star is eclipsed by the other, producing a variation in the amount of light that reaches our eyes. By comparing this star from day to day with the star just a short distance to the southeast of it, which does not vary in brightness, we can observe for ourselves this change in the light of Beta Lyræ. There are a number of stars in the heavens that vary in brightness in the same manner as Beta Lyræ, and they are called eclipsing-variable stars.

On the line connecting Beta Lyræ with the star southeast of it and one-third of the distance from Beta to this star, lies the noted Ring Nebula in Lyra, which is a beautiful object even in a small telescope. It consists of a ring of luminous gas surrounding a central star. The star shines with a brilliant, bluish-white light and is visible only in powerful telescopes though it is easily photographed since it gives forth rays to which the photographic plate is particularly sensitive. In small telescopes the central part of this nebula appears dark but with a powerful telescope a faint light may be seen even in the central portion of the nebula. This is one of the most interesting and beautiful telescopic objects in the heavens.

It is in the general direction of the constellation of Lyra that our solar system is speeding at the rate of more than a million miles a day. This point toward which we are moving at such tremendous speed lies alittle to the southwest of Vega, on the border between the constellations of Lyra and Hercules, and is spoken of as The Apex of the Sun's Way.

August—Sagittarius

In the southern sky we have this month the constellation of Sagittarius, The Archer, which is just to the east of Scorpio and a considerable distance south of Lyra. It can be recognized by its peculiar form, which is that of a short-handled milk dipper, with the bowl turned toward the south and a trail of bright stars running from the end of the handle toward the southwest. This is one of the zodiacal groups which containno first-magnitude stars, but a number of the second and third magnitude. It is crossed by the Milky Way, which is very wonderful in its structure at this point. Some astronomers believe that here—among the star-clouds and mists of nebulous light which are intermingled with dark lanes and holes, in reality dark nebulæ—lies the center of the vast system of stars and nebulæ in which our entire solar system is but the merest speck. Some of the grandest views through the telescope are also to be obtained in this beautiful constellation of Sagittarius, which is so far south that it is seen to better advantage in the tropics than in the mid-latitudes of the northern hemispheres.

One of the most beautiful constellations of the northern hemisphere is Cygnus, The Swan, which is in the zenith in mid-latitudes about nine o'clock in the evening the middle of September. It lies directly in the path of the Milky Way which stretches diagonally across the heavens from the northeast to the southwest at this time. In Cygnus, the Milky Way divides into two branches, one passing through Ophiuchus and Serpens to Scorpio, and the other through Sagitta and Aquila to Sagittarius, to meet again in the southern constellation of Ara, just south of Scorpio and Sagittarius. On clear, dark evenings, when there is no moonlight, this long, dark rift in the Milky Way can be seen very clearly. In Cygnus, as in Ophiuchus, Scorpio, and Sagittarius we find wonderful star-clouds, consisting of numberless stars so distant from us and, therefore, so faint that they do not appear as distinct points of light except in the greatest telescopes. It is the combined light from these numberless stars that cannot be seen separately that produces the impression of stars massed in clouds of nebulous light and gives to this girdle of the heavens its name of the Milky Way. In Cygnus, as in a number of other constellationsof both hemispheres, the Milky Way is crossed by dark rifts and bars and is very complicated in its structure. It is in Cygnus, also, that one may see with the aid of powerful telescopes the vast, irregular, luminous nebulæ, that are like great clouds of fiery mist. These nebulæ are of enormous extent, for they cover space that could be occupied by hundreds of stars.

September—Cygnus

Cygnus is a constellation that is filled with the wonders and mysteries of space and that abounds in beautiful objects of varied kinds. It is a region one never tires of exploring with the telescope. The principal stars in Cygnus form the well-known Northern Cross, with the beautiful, white, first-magnitude star Deneb, or Arided, as it is sometimes called, at the top of the cross, and Albireo, the orange-and-blue double star at the foot. Albireo, among all the pairs of contrastinghues, has the distinction of being considered the finest double star in the heavens for small telescopes. This star marks the head of The Swan, as well as the foot of the Northern Cross, and Deneb marks the tail of The Swan. A short distance to the southeast of Deneb, on the right wing of The Swan, is a famous little star, 61 Cygni, barely visible to the naked eye and forming a little triangle with two brighter stars to the east. This star has the distinction of being the first one to have its distance from the solar system determined. The famous mathematician and astronomer Bessel accomplished this difficult feat in the year 1838. Since that day, the distances of many stars have been found by various methods, but of all these stars only four or five are known to be nearer to us than 61 Cygni. Its distance is about eight light-years, so its light takes about eight years to travel the distance that separates it from the solar system. As a result, we see it not as it is tonight, but as it was at the time when the light now entering our eyes first started on its journey eight years ago. 61 Cygni is also a double star, and the combined light of the two stars gives forth only one-tenth as much light as our own sun. Most of the brilliant first-magnitude stars give forth many times as much light as the sun; but among the fainter stars, we find some that appear faint because they are very distant, and some that are faint because they are dwarf stars and have little light to give forth. To the class of nearby, feebly-shining dwarf stars 61 Cygni belongs. Deneb, on the other hand, is one ofthe giant stars, and is at an immeasurably great distance from the solar system.

Just south of Cygnus in the eastern branch of the Milky Way lie Sagitta, The Arrow, and Aquila, The Eagle. Not far to the northeast of Aquila is the odd little constellation of Delphinus, The Dolphin, popularly referred to as Job's Coffin. There will be no difficulty in finding this small star-group, owing to its peculiar diamond-shaped configuration. Its five principal stars are of the fourth magnitude. It is in the constellation of Delphinus that the most distant known object in the heavens is located. This is the globular star cluster known only by its catalogue number of N.G.C. 7006. It is estimated to be at a distance of 220,000 light-years from the earth.

Sagitta, The Arrow, lies midway between Albireo and the brilliant Altair in Aquila. The point of the arrow is indicated by the star that is farthest east; and the feather, by the two faint stars to the west. Like Delphinus, this constellation is very small and contains no objects of particular interest.

Altair (Flying Eagle) is the brilliant white star of the first magnitude in Aquila and is attended by two fainter stars, one on either side, at nearly equal distances from it. These two stars serve readily to distinguish this star, all three stars being nearly in a straight line. Altair is one of the nearer stars, its distance from the earth being about sixteen light-years. It gives forth about ten times as much light as the sun.

September—Delphinus, Aquila and Sagitta

We cannot leave the constellation of Aquila without referring to the wonderful temporary star or nova, known as Nova Aquilæ No. 3 (because it was the third nova to appear in this constellation), which appeared in the position indicated on the chart upon the eighth of June, 1918. A few days previous to this date, there was in this position an extremely faint star, invisible to the naked eye and in small telescopes. This fact became known from later examinations of old photographs of this region that had been taken at the Harvard College Observatory, where the photographing of the heavens is carried on regularly for the purpose of having a record of celestial changes and happenings. Clouds prevented the obtaining of any photographs of this part of the heavens on the four nights preceding the eighth of June, but on this evening there shone in the place of the faint telescopic star, a wonderful temporary star, or nova, which was destined on the nextevening to outshine all stars in the heavens, with the exception of the brightest of all, Sirius, which it closely rivaled in brilliancy at the height of its outburst. Within less than a week's time, this faint star in the Milky Way for some mysterious reason increased in brightness many thousandfold. Such outbursts have been recorded before, but on rare occasions, however. No star since the appearance of the nova known as Kepler's Star, in the year 1604, which at its greatest brilliancy rivaled Jupiter, shone with such splendor or attracted so much attention as Nova Aquilæ. In the year 1901, there appeared in the constellation of Perseus a star known as Nova Persei which at its brightest surpassed Vega, but its splendor was not as great as that of the wonderful nova of 1918.

It speaks well for the zeal and interest of amateur astronomers, as well as for their acquaintance with the stars, that Nova Persei was discovered by an amateur astronomer, Dr. Anderson, and that among the deluge of telephone calls and telegrams received at the Harvard College Observatory on the night of June 8th, announcing independent discoveries of the "new star," were many from non-professional astronomers.

Like all stars of this class, Nova Aquilæ No. 3 sank rapidly into oblivion. In a few weeks it was only a third-magnitude star; a few weeks more and it was invisible without a telescope. Many wonderful and interesting changes have been recorded in the appearance of this star, however, even after it became visible only in the telescope. Soon after its outburst itappeared to develop a nebulous envelope, as have other novas before it. It showed in addition many of the peculiarities of the nebulæ, though the central star remained visible as before the outburst.

Astronomers are still in doubt as to the cause of these outbursts, which certainly indicate celestial catastrophies of some form on a gigantic scale. All novas possess one characteristic in common—that of appearing exclusively in the Milky Way; and another characteristic is the development of a nebular envelope after the outburst of greatest brightness. In some cases temporary stars have been known to be variable in brightness for years before the great outburst. Such a star was Nova Aquila, for the examination of photographs of this region taken some years previous showed variations in its brightness for a period of thirty years at least.

Up to the beginning of this century only about thirty novas had been discovered. Since that date, thanks to the vigilance of the astronomers of today and to the aid of photography, more have been discovered than in all the preceding centuries. These outbursts of new stars appear to be not so rare as the earlier astronomers believed, though great outbursts as brilliant as that of Nova Aquila are very uncommon.

The constellations that will be found nearest the meridian in early October evenings are the circumpolar constellations Cepheus and Cassiopeia, and in the southern sky, Capricornus and Aquarius.

Cepheus, The King, and Cassiopeia, his Queen, of whom we shall have more to say later in connection with the constellations of Andromeda and Perseus, sit facing the north pole of the heavens opposite Ursa Major, The Great Bear, familiar to us under the name of The Big Dipper. The foot of Cepheus rests upon the tail of the Little Bear, and the star farthest north in the diagram is in the left knee. The head is marked by a small triangle of faint stars, shown in the diagram. One of these three faint stars—the one farthest east—known as Delta Cephei, is a very remarkable variable star, changing periodically in brightness every five and one-third days. Its name has been given to a large class of variable stars—the Cepheid variables—that resemble Delta Cephei in being giant suns, faint only because they are at very great distances from the earth, and varying in brightness with the greatest regularity in periods that range from a few hours to several weeks. It has been found that the longer the period of light change the greater is the star in sizeand brightness. The Cepheids of longest period are 10,000 times more brilliant than our own sun. Cepheus contains no very bright or conspicuous stars. Alpha Cephei, the brightest star in the group, marks The King's right shoulder. It is the star farthest to the west in the diagram, and is only a third-magnitude star.

October—Cassiopeia and Cepheus

Cassiopeia is a constellation with which every one in the northern hemisphere should be familiar, owing to its very distinctive W-shape and its far northern position, which brings it conspicuously into view throughout the clear fall and winter evenings. Cassiopeiais pictured in all star atlases that show the mythological figures, with her face toward the north pole. The stars in the W outline the body. Alpha, the star farthest south in the diagram marks the breast of Cassiopeia. Her head and uplifted hands are represented by faint stars south of Alpha. This star is occasionally referred to by its Arabic name of Schedir. Beta, the leader of all the stars in the W in their daily westward motion, is also known by an Arabic name, Caph.

In the constellation of Cassiopeia there appeared in the year 1572A.D., a wonderful temporary star which suddenly, within a few days' time, became as brilliant as the planet Venus and was clearly visible in broad daylight. This star is often referred to as Tycho's Star, because it was observed, and its position very accurately determined, by Tycho Brahe, one of the most famous of the old astronomers. This star remained visible to every one for about sixteen months, but it finally faded completely from view, and it is believed that a faint, nebulous red star, visible only in the telescope and close to the position recorded by Tycho, represents the smoldering embers of the star that once struck terror to the hearts of the superstitious and ignorant among all the nations of Europe, who took it to be a sign that the end of the world was at hand.

Both Cassiopeia and Cepheus lie in the path of the Milky Way, which reaches its farthest northern point in Cassiopeia and passes from Cepheus in a southerly direction into the constellation of Cygnus.

October—Aquarius and Capricornus

Turning now to southern skies, we find on and to the west of the meridian at this time the rather inconspicuous zodiacal constellation of Capricornus, The Goat. It contains no stars of great brightness and is chiefly remarkable for the fact that it contains one of the few double stars that can be seen without the aid of a telescope. The least distance in the heavens that the unaided human eye can separate is about four minutes of arc. The star Alpha in Capricornus is made up of two stars separated by a distance of six minutes of arc, so that any one can readily see that it consists oftwo stars very close together. This star, Alpha, will be found in the extreme western part of the constellation, and can best be located in conjunction with the star Beta, which is slightly brighter and lies but a short distance almost due south of Alpha, the two stars standing somewhat alone in this part of the heavens.

To the north and east of Capricornus we find Aquarius, which is also a zodiacal constellation. Aquarius is the Water-Bearer, and the water jar which he carries is represented by a small, but distinct, Y of stars from which flows a stream of faint stars toward the southeast and south. Aquarius, like Capricornus, is a rather uninteresting constellation, as it is made up of inconspicuous third- and fourth-magnitude stars. The entire region covered by these two groups of stars is remarkably barren, since it contains not a single first- or even second-magnitude star and little to attract the observer's eye.

To relieve the barrenness of this region, there appears just to the south of Aquarius and southeast of Capricornus, sparkling low in the southern sky on crisp October evenings, the beautiful first-magnitude star Fomalhaut in the small southern constellation of Piscis Australis, The Southern Fish. This star is the farthest south of all the brilliant first-magnitude stars that can be seen from the middle latitudes of the Northern Hemisphere. The constellation in which it lies is so close to the southern horizon in our latitudes that it cannot be seen to any advantage, and it is at best very inconspicuous, containing no other objectsof interest. Fomalhaut cannot be mistaken for any other star visible at this time of year in the evening, since it stands in such a solitary position far to the south. At the time of which we are writing it will be found a few degrees east of the meridian.

Directly south of Cassiopeia and Cepheus, the circumpolar constellations with which we became acquainted last month, and almost overhead in our latitudes in the early evening hours of November, lie Pegasus, The Winged Horse, and Andromeda, The Woman Chained.

According to the legend, Cepheus was king of Ethiopia, and Cassiopeia was the beautiful, but vain, queen who dared to compare herself in beauty with the sea-nymphs. This so enraged the nymphs that, as a punishment for her presumption, they decided to send a terrible sea-monster to ravage the coast of the kingdom. The king and queen, upon consulting the oracle, found that the only way to avert this calamity would be to chain their daughter Andromeda to the rocks and permit the monster to devour her.

November—Andromeda and Pegasus

As the story goes, the valiant hero, Perseus, chanced to be riding through the air on his winged horse and saw, far beneath him the beautiful maiden chained to the rocks and the frightful monster approaching to devour her. He immediately went to the rescue, and, after a terrible struggle with the monster, succeeded in overpowering him and thus saved the maiden from adreadful fate. Perseus and the fair Andromeda were married shortly afterward, and at the end of a happy life the pair were transferred to the heavens. Cassiopeia, the vain queen, was ordered to be bound to a chair and, with the king Cepheus at her side, to be swung continually around the north pole of the heavens that she might be taught a lesson in humility.

The constellation Cetus, representing the sea-monster, will be found to the southeast and south of Pisces, The Fishes, which lie south of Andromeda and Pegasus.

The Great Square in Pegasus is the most conspicuousconfiguration of stars to be seen in the heavens in autumn evenings. The star that marks the northeastern corner of The Great Square belongs to the constellation of Andromeda and marks the head of the maiden, who is resting upon the shoulders of Pegasus, The Winged Horse. The three bright stars nearly in a straight line outline the maiden's body, Alpha, or Alpheratz, as it is called, being the star in the head, Beta or Mirach in the waist, and Gamma or Almach in the left foot. The last-named star, which is farthest to the northeast in the diagram, was, in the opinion of the noted astronomer Herschel, the finest double star in the heavens. The two stars into which the telescope splits it are of the beautifully contrasted shades of orange and sea green.

A second most interesting object in Andromeda and one of the finest in the entire heavens is The Great Andromeda Nebula, which is faintly visible without the aid of a telescope as a hazy patch of light. It is believed that in reality this nebula is a great universe composed of many thousands of stars so distant that no telescope can show the individual members and that the light from it takes many thousands of years to span the abyss that separates it from the solar system. Some magnificent photographs of The Great Andromeda Nebula have been taken with powerful telescopes. It is through the use of photography that the nebulæ can best be studied, for a photographic plate after long exposure, reveals a wonderful detail in the structure of these objects that the human eyefails to see. On a clear, dark evening one may find The Great Andromeda Nebula by the aid of two faint stars with which it makes a small triangle, as shown in the chart. This nebula is the only one of the spiral nebula that can be seen in these latitudes without the aid of a telescope, though there are several spiral nebulæ in the southern heavens that can be thus seen.

Lying to the northwest of The Great Square in Pegasus are a number of faint stars that outline the shoulders and head of the winged steed, while the stars to the southwest of the square outline his forelegs. The creature is represented without hind quarters in all star atlases. The space within The Great Square contains no bright stars, and as a result, the outline of the square stands out with great distinctness. There are, in fact, no stars of the first magnitude in either Pegasus or Andromeda, though there are a number of the second and third magnitude which very clearly show the distinctive forms of these two star-groups.

Pisces, The Fishes, the constellation just south of Andromeda and Pegasus, is the first of the twelve zodiacal constellations. It consists of the southern fish, lying in an east-to-west direction, and the northern fish, lying nearly north and south, the two touching at the southeastern extremity of the constellation.

November—Pisces

There is in Pisces not a single bright star, and its only point of interest is to be found in the fact that it contains the point, marked by the cross and letter V in the diagram, that is known variously as "the vernalequinox," "the equinoctial point" and "The First Point in Aries." This is a very important point of reference in the heavens, just as the meridian of Greenwich is for the earth, and it marks the point where the sun crosses the equator going north in the spring. Owing to the Precession of the Equinoxes, as it is called, this point is gradually shifting its position westward through the zodiacal constellations at a rate that will carry it completely around the heavens through the twelve zodiacal groups in a period of 25,800 years.Since the beginning of the Christian era, this point has backed from the constellation of Aries, which lies just east of Pisces, into Pisces, though it still retains its name of "The First Point in Aries."

The eastern half of the sky on early December evenings is adorned with some of the finest star-groups in the heavens; but as we are considering for each month only the constellations that lie on or near the meridian in the early evening hours, we must turn our eyes for the present from the sparkling brilliants in the east to the stars in the less conspicuous groups of Aries, The Ram, and Cetus, The Whale. We will also become acquainted this month with the beautiful and interesting constellation of Perseus, the hero of mythical fame to whom we referred last month in connection with the legend of Cepheus and Cassiopeia. Cetus, you will recall, represents the sea-monster sent to devour Andromeda, the daughter of Cepheus and Cassiopeia. We have included the constellation of Andromeda in our diagram for this month, since it is so closely associated in legend with the constellations of Perseus and Cetus, though we also showed it last month.

The brightest star in Perseus, known as Alpha Persei, is at the center of a curved line of stars that is concave or hollow toward the northeast. This line of stars is called the Segment of Perseus, and it liesalong the path of the Milky Way, which passes from this point in a northwesterly direction into Cassiopeia. According to the legend, Perseus, in his great haste to rescue the maiden from Cetus, the monster, stirred up a great dust, which is represented by the numberless faint stars in the Milky Way at this point. The star Alpha is in the midst of one of the finest regions of the heavens for the possessor of a good field-glass or small telescope.

A short distance to the southwest of Alpha is one of the most interesting objects in the heavens. To the ancients, it represented the baleful, winking demon-eye in the head of the snaky-locked Gorgon, Medusa, whom Perseus vanquished in one of his earliest exploits and whose head he carried in his hand at the time of the rescue of Andromeda. To the astronomers, however, Algol is known as Beta Persei, a star that has been found to consist of two stars revolving about each other and separated by a distance not much greater than their own diameters. One of the stars is so faint that we speak of it as a dark star, though it does emit a faint light. Once in every revolution the faint star passes directly between us and the bright star and partly eclipses it, shutting off five-sixths of its light. This happens with great regularity once in a little less than three days. It is for this reason that Algol varies in brightness in this period. There are a number of stars that vary in brightness in a similar manner. Their periods of light-change are all very short, and the astronomers call them eclipsing variables. At itsbrightest, Algol is slightly brighter than the star nearest to it in Andromeda, which is an excellent star with which to compare it.

December—Perseus, Aries and Cetus

Perseus is another one of the constellations lying in the Milky Way in which temporary stars or novas have suddenly flashed forth. At the point indicated by a cross in the diagram, Dr. Anderson, an amateur astronomer of Scotland, found on February 21, 1901, a new star as brilliant as the pole-star. On the following day it became brighter than a star of the first magnitude. A day later it had lost a third of itslight, and in a few weeks it was invisible without the aid of a telescope. In a year it was invisible in all except the most powerful telescopes. With such telescopes, it may still be seen as a very faint nebulous light.

Triangulum and Aries are two rather inconspicuous constellations that lie on, or close to, the meridian at this time. There is nothing remarkable about either of these groups, except that Aries is one of the twelve zodiacal constellations. Some centuries ago, the sun was to be found in Aries at the beginning of spring and the position it occupies in the sky at that time was called the First Point in Aries. As this point is slowly shifting westward, as we have explained elsewhere, the sun is now to be found in Pisces, instead of Aries at the beginning of spring and does not enter Aries until a month later. Pisces was one of the constellations for November and we showed in that constellation the present position of the sun at the beginning of spring.

Two stars in Aries—Alpha and Beta—are fairly bright, Alpha being fully as bright as the brightest star in Andromeda. Beta lies a short distance to the southwest of Alpha, and a little to the southwest of Beta is Gamma, the three stars forming a short curved line of stars that distinguishes this constellation from other groups. The remaining stars in Aries are all faint.

Just south of Aries lies the head of Cetus, The Whale. This is an enormous constellation that extendsfar to the southwest, below a part of Pisces, which runs in between Andromeda and Cetus. Its brightest star, Beta, Diphda, or Deneb Kaitos, as it is severally called, stands quite alone not far above the southwestern horizon. It is almost due south of Alpha Andromedæ, the star in Andromeda farthest to the west, which it exactly equals in brightness. The head of Cetus is marked by a five-sided figure composed of stars that are all faint with the single exception of Alpha, which is fairly bright, though inferior to Beta or Diphda.

Cetus, though made up chiefly of faint stars, and on the whole uninteresting, contains one of the most peculiar objects in the heavens, the star known as Omicron Ceti or Mira (The Wonderful). This star suddenly rises from invisibility nearly to the brightness of a first-magnitude star for a short period once every eleven months. Mira was the first known variable star. Its remarkable periodic change in brightness was discovered by Fabricius in the year 1596, so its peculiar behavior has been under observation for three hundred and twenty-five years. It is called a long-period variable star, because its variations of light take place in a period of months instead of a few hours or days, as is the case with stars such as Algol. Mira is not only a wonderful star, it is a mysterious star as well, for the cause of its light-changes are not known, as in the case of Algol where the loss of light is produced by a dark star passing in front of a brighter star. Mira is a deep-red star, as are all long-periodvariable stars that change irregularly in brightness. It is visible without a telescope for only one month or six weeks out of the eleven months. During the remainder of this time, it sometimes loses so much of its light that it cannot be found with telescopes of considerable size. Its periods of light-change are quite variable as is also the amount of light it gains at different appearances.

It is believed that the cause of the light-changes of Mira is to be found within the star itself. It has been thought that dense clouds of vapors may surround these comparatively cool, red stars and that the imprisoned heat finally bursts through these vapors and we see for a short time the glowing gases below; then the vapors once more collect for a long period, to be followed by another sudden outburst of heat and light.

It is interesting to remember in this connection that our own sun has been found to be slightly variable in the amount of light and heat that it gives forth at different times, and the cause of its changes in light and heat are believed to lie within the sun itself.

As one travels southward from the mid-latitudes of the northern hemisphere into the tropics our familiar circumpolar constellations sink lower and lower in the northern heavens and strange and unfamiliar star-groups rise gradually above the southern horizon. If we make our southward journey in the winter months the first of the southern constellations to come fully into view is the small star-group just south of Lepus known as Columba (The Dove), whose brightest star Phact is of the second magnitude. A line drawn from Procyon to Sirius and extended as far again brings us to this star and a line from Betelgeuze to Sirius extended an equal distance brings us to Zeta Argus which is equal to Phact in brightness. The two lines intersecting at Sirius make the "Egyptian X" as it is called.

Magnificent, blue-white Canopus, the most brilliant star in the heavens next to Sirius, a veritable diamond sparkling low in the southern sky, now commands our unqualified admiration. Canopus lies about 35° south of Sirius and is invisible north of the 37th parallel of latitude. At nine o'clock in the evening of February 6th it can be seen just above the southern horizon inthat latitude and is then a conspicuous object in Georgia, Florida and the Gulf States.

"The star of Egypt whose proud lightNever hath beamed on those who restIn the White Islands of the West."

writes Moore of Canopus in "Lalla Rookh."

Along the Nile Canopus was an object of worship as the god of waters. At the time of their erection, 6400B.C., a number of temples in Upper Egypt were oriented so as to show Canopus at sunrise at the autumnal equinox, and other temples erected many centuries later were oriented in a similar manner. In China, as late as 100B.C., and in India also Canopus was an object of worship.

The astronomer tells us that Canopus is immeasurably distant from the earth. It has been estimated to be forty thousand times more luminous than our sun.

Canopus is located in the constellation of Argo Navis which is the largest and most conspicuous constellation in the heavens. In addition to Canopus it contains a number of second- and third-magnitude stars and is subdivided for convenience into Puppis, The Prow; Carina, The Keel; and Vela, The Sails. Huge as it is, Argo Navis represents only half of a ship for the stern is lacking. According to the legend this ship was built by Argos, aided by Pallas Athene, for Jason, the leader of the expedition of the fifty Argonauts who sailed from Greece to Colchis in search of the golden fleece. Pallas Athene placed in the bowof the ship a piece of timber from the speaking oak of Dodona to guide the crew and warn them of dangers and after the voyage the ship was supposed to have been placed in the heavens.

Southern Constellations—1. In February

In Argo Navis is one of the finest telescopic objects in the heavens, the Keyhole Nebula, as it is usually called, from a peculiar-shaped dark patch in its brightest part. On the border of this nebula is the deep-red Wonder Star of the southern hemisphere, Eta Argus, which varies suddenly and unexpectedly in brightnessbetween the seventh and first magnitudes. In 1843 it burst forth with a splendor rivaling Sirius and maintained this brilliancy for nearly ten years and then slowly waned in brilliancy until it disappeared to the unaided eye in 1886. The surrounding nebula also seems to share in its peculiar fluctuations of brightness. Eta Argus is now a star of the seventh magnitude and since it is still varying fitfully in brightness it is believed that the history of its light-changes is not complete.

Among the constellations of the southern heavens near the meridian in February we see in addition to Argo Navis the constellations of Dorado, The Goldfish; Hydrus, The Serpent, and Tucana, The Toucan. Though insignificant in appearance Dorado contains what was described by Sir John Herschel as one of the most extraordinary objects in the heavens, a worthy rival of The Great Orion Nebula and in some respects very similar to it, The Great Looped Nebula, "the center of a great spiral." In Dorado also is located The Greater Magellanic Cloud which looks like a detached portion of the Milky Way though it is far removed from it. To the naked eye it resembles a small white cloud about 4° in extent. In the telescope it bears a close resemblance to a typical portion of the Milky Way. A similar formation known as The Lesser Magellanic Cloud is located in Hydrus. It has been estimated that the distance of The Lesser Cloud is 80,000 light-years and that it is receding from us.

In Tucana is located one of the finest globular starclusters in the heavens, known as 47 Tucanæ. This cluster and Omega Centauri, a globular star cluster in Centaurus, are the two nearest of all the globular clusters. They are distant from the earth about 22,000 light-years and it is known that the combined light of the thousands of stars of which each cluster is composed is about one million times that of our own sun.

In the western sky in the southern hemisphere in February may be seen the brilliant, white, first-magnitude star Achernar in the river Eridanus, the long, winding constellation that, we recall, starts near the brilliant Rigel in Orion and disappears from the view of northern observers below the southern horizon, extending its course far into the southern hemisphere. Achernar means "The End of the River" and this is nearly its position in the constellation.

Though Argo Navis is the largest and most important constellation of the southern hemisphere, Crux, The Southern Cross, far-famed in story and legend as well as for its historical associations, is beyond a doubt the most popular.

The best time to view the Southern Cross is in June or July when it is near the meridian. It is not seen to advantage in the months of January or February. It then lies on its side and close to the horizon and therefore is dimmed by atmospheric haze so that it almost invariably is a disappointing object to the tourist from the north who usually views it for the first time in one of these months. The Cross is viewed to advantage in the latitude of Rio or Valparaisoand it is best seen from the Straits where it rides high overhead. It is not seen to advantage from the latitudes of Cuba or Jamaica. It is small, only 6° in extent from north to south and less in width and it lies in the most brilliant portion of the Milky Way which is here a narrow stream only three or four degrees wide. Directly below the Cross is the noted Coal Sack, apparently a yawning chasm in the midst of its brilliant surroundings though probably in reality a dark nebula. Viewed with the telescopes a number of stars are to be seen projected on this dark background.

The Southern Cross is to the inhabitants of the southern hemisphere what the Big Dipper is to those who dwell in the northern hemisphere—an infallible timepiece. The upright of the Cross points toward the south pole of the heavens which lies in a region where there is a singular dearth of bright stars, the nearest star to the south pole being a faint fifth-magnitude star called Sigma Octantis. When seen in the southeast or southwest the Cross lies on its side, but when passing the meridian it stands nearly upright. Humboldt, referring to this fact, says:

"How often have we heard our guides exclaim in the savannahs of Venezuela and in the desert extending from Lima to Truxillo, 'Midnight is past, the Cross begins to bend.'"

By the explorers of the sixteenth century the Cross was taken as a sign of heaven's approval of theirattempt to establish the Christian religion in the wilds of the New World. This thought is beautifully expressed in Mrs. Hemans' lines in "The Cross of the South."

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