Part 2

THE CONSTELLATIONS OF THE SOUTH: MODERN GROUPS

When we speak of the southern constellations, everyone thinks of the Southern Cross, and every traveller coming south for the first time is eager to see it. Some are disappointed because it is small and irregular, but it is very brilliant, and lies in an extremely rich region of the Milky Way. Very beautiful, too, is the way in which it is seen rising on its side and gradually becoming upright as it reaches its greatest height above the horizon, then sloping again as it glides westward.

The Cross seems to have been first so named by the Spanish explorer Amerigo Vespucci, at the beginning of the sixteenth century, and it was also described in letters by the Florentine Andrea Corsali, who says it is so beautiful that in his opinion no other constellation in the sky is worthy to be compared with it. Some think, however, that the stars had already been recognised as forming a Cross as early as the thirteenth century, because Dante in his Purgatory speaks of four stars which glorified the southern sky; but he does not say they were in the form of a cross, and he tells us that they had never been seen before by mortal man except by our first parents, whose original dwelling-place he sets in the southern hemisphere. This negatives the suggestion that some traveller had described them to him.

About the same time as the Cross, other groups were named by sailors and travellers in the part of the sky round about the south pole, for this region had been left a blank by the framers of the ancient constellations, doubtless because they lived too far north to see it. Some students of astronomy in the Middle Ages concluded that there really were no stars in this part, and Ristoro of Arezzo gravely argued that this proved the absence of any land further south than India and Ethiopia; for where there are no stars to pour down influences on the earth no animals can live, and therefore no vegetation is needed for their food, and no land for it to grow on.

The new constellations were mostly named after strange birds and fishes seen by explorers in their southern voyages, and they were admitted to scientific astronomy by Bayer, who made a map of the skies in 1604. He also introduced the plan of naming each star in a constellation by a Greek letter, the brightest of each constellation usually being called Alpha, the next brightest Beta, and so on. One of these constellations is Grus, the Crane (originally called the Flamingo), and it is convenient to be familiar with it, because from it we may easily identify several others. The chief stars of Grus form a striking curve with a bright star close beside it. This bright star is Alpha Gruis, and the brightest in the curve is Beta. A line through Alpha and Beta leads in one direction to the brightest star of the Phoenix, in the other direction to the brightest of the Indian; a line through Alpha and the little naked-eye double Delta takes one to Pavo, the Peacock; a line through Gamma (at one end of the curve) and Alpha goes to the brightest star in the Toucan. And these are all the modern groups containing bright stars except the Southern Triangle, near the Pointers to the Cross (see p. 6), and Columba, the Dove, not far from Sirius, each of which has one star brighter than third magnitude. We may, however, also notice Alpha Hydri, the brightest star in the small Water-Snake, close to the bright star Achernar, and Alpha Doradūs, the brightest of the Sword-Fish, between Canopus and Achernar.

Stars are classified by astronomers in “magnitudes,” i.e. degrees of brightness, those of first magnitude being the brightest. Stars below sixth magnitude cannot be seen with the naked eye.

In the eighteenth century the French astronomer Lacaille, who did much excellent work in the southern hemisphere with a tiny telescope of only half an inch aperture, had the unhappy idea of filling up the spaces still left empty with scientific instruments. It is easy to make Birds of Paradise and Flying Fishes out of the stars, but such things as telescopes, easels, and sextants do not lend themselves to irregular groups, and they are very much out of place among the mythical beasts and heroes which we are accustomed to see on our star-maps. Fortunately the beginner need not learn to recognise these intruders, for there are no bright stars in them, although there are many interesting objects for telescopic study. We need only note that Octans, the Octant, occupies the region in which the south pole is situated, which is quite bare of bright stars. The pole itself may be found by drawing a line from head to foot of the Cross and carrying it on about four times as far again; or if the Cross is invisible, the pole may be found near the middle of a line from Canopus to Alpha Pavonis.

THE CONSTELLATIONS OF THE SOUTH: ANCIENT GROUPS

Let us turn once more to the Southern Cross to find the ancient constellations. It is both ancient and modern itself, for its stars were known to the Greeks of Alexandria, but were included in the Centaur. The latter, like all those shown in the accompanying illustration, is of great antiquity, and probably of Babylonian origin. The two stars which we call the Pointers to the Cross are Alpha and Beta of the Centaur, and mark his forefeet. Another conspicuous pair, Delta and Gamma, are on his horse’s body, while his man’s shoulders are marked by many bright stars, and the head is formed by a little group. His arm stretches out through bright Eta to Kappa, which is very close to Beta Lupi. For the Centaur and Lupus form one large and very brilliant group, and were perhaps connected with the little constellation of Ara, the Altar, upon which the Centaur seems to have been imagined as offering the creature which we now know as the Wolf, though its older name was simply the Beast. Aratus, a Greek poet of about 300 B.C., to whom we owe the earliest description extant of the ancient constellations, says of the Centaur:

“His right hand he ever seems to stretch Before the Altar’s circle. The hand grasps Another creature, very firmly clutched, The Wild Beast,—so the men of old it named.”

On the other side of the Cross is another splendid constellation, the Ship Argo, which covers a large space of the sky with many bright stars, among them Canopus, the brightest in the whole heavens except Sirius. For convenience this large constellation has been divided into four—the Keel, the Poop, the Mast, and the Sails.

Sirius is north of Canopus, in the constellation of the Great Dog—Orion’s Dog, as it is often called, for Orion is a hunter with two dogs; but the Little Dog is in the northern hemisphere, and Orion himself has his head in the north and his feet in the south, his famous belt and sword lying just south of the equator. Thus he is visible all over the world, and only at the poles would his feet or his head never rise above the horizon. Beneath his feet is the little Hare, as Aratus says:

“And ceaselessly beneath Orion’s feet The Hare is ever chased.”

Four stars of the Hare (α, β, γ, δ), which form a small square, were called by the Arabs the “Throne of the Giant” (i.e. of Orion); or sometimes “those which quench the thirst of the camel,” in allusion to the river of the Milky Way which flows close by. Orion is mentioned in the books of Job and Isaiah, and also by Hesiod and Homer.

Above the Centaur and the Ship Argo stretches the long straggling constellation of Hydra, the Water-Snake. Its head reaches beyond the equator into the northern hemisphere, but the beautiful red star Alphard is in our hemisphere. This Snake is oddly connected with a Crow and a Cup, which are somehow perched on its back. (I have seen a snake pursued by an Indian crow, which kept pecking at its tail until the snake found refuge in a stream.) Crater, the Cup, has no bright stars; Corvus, the Crow, is an irregular little square which sailors call Spica’s Spanker, a spanker being a sail of this shape, and two stars of the four point to Spica, the bright star of the Virgin.

Virgo, the Virgin, is one of the constellations of the Zodiac, that zone of stars which marks the apparent pathway of sun, moon, and planets in the sky. All the twelve zodiacal constellations can be seen in both hemispheres, but those south of the equator, which are least well seen in northern countries, are of course the best seen in the south. These are the Scales, Scorpion, Archer, Sea-Goat, and Water-carrier, with a very small part of the Fishes, and the part of Virgo which contains her brightest star, Spica, the Ear of Corn held in her hand. The Romans called her the Goddess of Justice, but these constellations were invented long before Rome was a great power, and the ear of corn shows that she was rather a goddess of the fields. They added that the Scales were her balance wherein she weighed the deeds of men, but this constellation was of much later origin than the Virgin: its place was earlier held by the Claws of the Scorpion. In some old books we find a compromise between the two ideas, for a pair of tiny scales is hung on the great claws of Scorpio.

Compare Aratus:

“The Virgin and the Claws, the Scorpion, The Archer and the Goat.”

Scorpio is a magnificent constellation as seen in the south. In England it merely creeps along the southern horizon in the pale summer skies, but in southern countries its whole splendid length rises high and shines, from the bright stars in its head and the ruby Antares on its back to the sting in its tail, represented by two stars close together.

Close behind Scorpio is Sagittarius, the Archer, also a brilliant constellation, with his bow strung ready to shoot the Scorpion; he is a centaur, like the figure near the Southern Cross. He is followed by Capricornus, a very strange animal, for it has the head and horns of a goat and the tail of a fish. As a modern writer quaintly says:

“A startling monster’s hybrid form Your eyes will there assail; That sign so often dubbed the Goat, Yet with a fish’s tail.”

Capricorn has very few bright stars. There are two in his goat’s head, of which the brightest, Alpha, is a beautiful naked-eye double, and there are two in his fish’s tail. These three figures—a Scorpion, Centaur-archer, and Capricorn—are carved on old Babylonian boundary-stones belonging to the second millennium B.C.

Following these is Aquarius, the Water-carrier, his shoulder marked by the star β, and his pot by four stars (α, γ, ζ, η), from which fall splashes and streams of faint stars, aptly representing the water which he is pouring out. He is a familiar figure to those who have lived in some countries of the East where water is all carried by hand.

From a Babylonian Boundary Stone now in the British Museum.]

This is a very watery part of the heavens, for the zodiacal pair of Fishes follows the Water-carrier (their only bright star in the northern hemisphere), and there is also a solitary Fish, Piscis Australis, swimming in the water poured out; while a little further east is the great Sea-Monster, which belongs to the northern group of Perseus and Andromeda and her parents Cepheus and Cassiopeia. Only the head of Cetus, the Sea-Monster, is in the northern hemisphere, but that contains its brightest star. Between the dim Sea-Monster and the bright Orion flows the winding River Eridanus: it rises near Orion’s foot, and now ends very far south in the bright star Achernar; but this star was not visible to Ptolemy when he drew up his star-catalogue in Alexandria, and the original Achernar, or Last-of-the-River, seems to have been what we now call Theta Eridani, which was much brighter some centuries ago than it is now. Al-Sufi, an Arab writer of the tenth century A.D., calls it a star of first magnitude.

To complete our survey of the constellations south of the equator we must add the tip of the Eagle’s wing, the legs of the Unicorn, and part of Ophiuchus with the Serpent he is strangling as he treads the Scorpion under foot (a gallant hero, to contend with both these enemies at once).

It is worth noting that just as the three stars of Orion’s belt mark the celestial equator in one part of the sky, so the three bright stars of the Eagle mark it in the opposite part (Altair, with β and γ on either side); but they are just north of it, and Orion’s belt is just south. As it is often interesting to know where the ecliptic lies, we may point out that the following southern stars lie near it: Spica, α Librae, Antares, α and β Capricorni (and in the north the Pleiades, Aldebaran, Regulus). It is also convenient to remember the positions of a few constellations as a guide to right ascension. Thus, Achernar is in the Ist hour, Canopus and Sirius are in the VIth, the Cross and Corvus in the XIIth, and the Bow of Sagittarius is in the XVIIIth.

Right ascension in the skies corresponds with longitude on earth, but is more often reckoned in time than in degrees. For instance, R.A. 1 hour 35 minutes, the right ascension of Achernar, means that this star will be on the meridian 1 hour 35 minutes later than the “first point of Aries”—that is, the point at which the equator cuts the ecliptic at the spring equinox, the fundamental point corresponding with Greenwich in earthly longitude.