December 13 1963 - Legends of the Stars

Everyone must be fascinated by the old myths associated with the star- patterns, and the Christmas season seemed to be a good time to present a programme about them. With me was Colin Ronan, who has made a special study of the ancient star-legends.

The first astronomers had no real idea about the nature of the stars. Since no star appeared as anything but a point of light, it was natural to suppose that they were small; since they showed no relative motions, it was equally natural to assume that they were fixed, revolving round the Earth once in twenty-four hours. It was thought, too, that all the stars lay at the same distance from us, probably fixed to some sort of solid sphere.

This sounds far-fetched today, when it is known that the stars are suns and that many of them are much larger and more luminous than the Sun we know. Yet we still have a legacy from the old sky watchers, since the constellation patterns which they formu­lated have never been changed.

Ptolemy of Alexandria, last of the great astronomers of Classical times, died about a.d. 180. In his best-known book, which has come down to us by way of its Arab translation, he virtually summarized the astronomical knowledge of his period. Altogether he enumerated forty-eight constellations; some were named after mythological gods and heroes (Orion, Hercules), while others were supposed to represent everyday creatures and inanimate objects (the Swan, the Fishes, the Cup). All Ptolemy's groups are still accepted, though their boundaries have been modified. Of course, the sky was not completely covered, since the far southern stars were never visible from the Mediterranean area, so that some of the groups near the south celestial pole have strangely modern names - the Microscope and the Octant, for instance.

Astronomers of the seventeenth and eighteenth centuries were not slow to form new constellations, often by 'stealing' areas from the older groups. Some of these have been accepted, and the total number of constellations is now almost ninety, but others were tacitly rejected. Perhaps this is just as well, since the names were cumbersome and the proposed groups totally unworthy of separate recognition. Typical examples are Sceptrum Brandenburgicum (the Sceptre of Brandenburg), Officina Typographica (the Printing Press) and Telescopium Herschellii (Herschel's Telescope - not to be confused with the modern Telescopium), all of which, together with others, are to be found on the star-maps drawn up by the German astronomer Bode about 1780.

Thirty years ago, a commission of the International Astrono­mical Union took the whole matter in hand, and fixed the boundaries of the various constellations with great precision. Even so, it cannot be said that the system is logical, and one is tempted to agree with Sir John Herschel, the great nineteenth-century astronomer, who said that 'the constellations seem to have been almost purposely named and delineated to cause as much confusion and inconvenience as possible. Innumerable snakes twine through long and contorted areas of the heavens, where no memory can follow them; bears, lions, and fishes, small and large, northern and southern, confuse all nomenclature.'

Neither do the constellations, in general, have outlines which correspond even remotely with the objects after which they are named. It takes a highly fertile imagination to make a hunter out of Orion, a bear out of the Great Bear, or a ship out of Argo Navis. Only in a few minor cases, such as the Triangle and the Northern Crown, are the names reasonably appropriate.

Another point of considerable importance is that there is no such thing as a 'constellation' in the real sense of the word. In most cases the various stars in any particular group are not associated with each other, and simply happen to lie in more or less the same direction as seen from the Earth. To show what is meant it will be best to consider Orion, the Hunter, which is among the most spectacular of all the constellations, and which dominates the evening sky during winter and early spring.

Orion is so distinctive that it can hardly be overlooked. It has seven bright stars of which two (Betelgeux and Rigel) are particu­larly prominent. The most casual glance shows that Betelgeux and Rigel are entirely different. Rigel is almost pure white, and exceptionally luminous; a recent estimate makes it about 50,000 times as powerful as the Sun, and its distance from us in the region of 900 light-years. Betelgeux has a strongly orange-red hue, and is not so luminous, but to compensate for this it is of immense size; its diameter is thought to be 250,000,000 miles, so that it is large enough to contain the entire orbit of the Earth round the Sun. It is 520 light-years away, so that the real distance between Betelgeux and Rigel is comparable to the distance between Betelgeux and ourselves. On the other hand Kappa Orionis or Saiph, the star in the lower left-hand corner of the Orion figure, has a distance of more than 2,000 light-years, and is not truly associated in any way with either Betelgeux or Rigel.

An even more graphic case is provided by Aldebaran, in Taurus - 'The Eye of the Bull', a brilliant orange-red star almost in line with Orion's belt. Extending from it may be seen a pattern of several much fainter stars, making a rough 'V', and comprising the Hyades cluster. It looks, at first sight, as though Aldebaran were situated in the Hyades, but this is not so; Aldebaran lies about half-way between the cluster and the Sun. The diagram makes this clear.

The same principle may be applied to the planets, which are relatively very close. When we say that a planet is 'in' a parti­cular constellation, such as Capricornus or Aquarius, what we really mean is that the planet is seen against a background of totally unrelated stars making up a chance pattern which has been given an arbitrary name. The pseudo-science of astrology, which is built around the planetary positions, is therefore totally without scientific basis.

Yet although the constellations are mere line-of-sight effects, and although few of them bear any resemblance to their chosen names, the old myths and legends are fascinating. Orion, for instance, was said to be the son of Neptune and Euryale, and boasted that he could conquer any creature which Earth could produce - whereupon Juno, who was jealous of him, caused a giant scorpion to appear out of the ground and bite Orion in the foot, killing him. Some say the pleadings of Diana, goddess of hunting, led to his being placed in the heavens directly opposite the scorpion (Scorpio), so that he should suffer no further harm from it. Orion and Scorpio may never be seen together; when one is above the horizon, the other is below. Another legend relates how Diana fell in love with Orion, and thus angered Apollo, who persuaded her to try her skill at archery by shooting at a certain object in the sea. She aimed, and hit the distant mark - which proved to be the head of Orion, who had been wading in the waters. Diana's arrow having killed him, the goddess placed him among the stars.

Orion, as befits a mighty hunter, has his retinue around him. In particular there are two Dogs, Canis Major and Canis Minor. The first contains Sirius, the brightest star in the sky; in point of fact it is much less luminous than a giant such as Rigel, and is a mere twenty-six times as brilliant as the Sun, but it is also one of our nearest stellar neighbours, and lies at a distance of eight and a half light-years. There are various other moderately bright stars in the group, but the outline of the Dog is not well marked. Canis Minor has one bright star, Procyon. The rather barren area between the Dogs is filled by Monoceros, the Unicorn, which has nothing to do with Orion and was added to the sky by Hevelius in 1690. On the other hand another small constellation, Lepus (the Hare), is one of Ptolemy's original forty-eight, presumably because the legends tell us that Orion was particularly fond of hunting hares. Lepus is found aptly enough, below the Hunter's feet.

Not far from Orion lies the constellation of Gemini, the Twins. The Twins themselves, Castor and Pollux, are represented by two bright stars unusually close together in the sky, though once more there is no real connection, since Castor is a full ten light-years farther away from us. The two may be found by using an extended line from Rigel through Betelgeux as a pointer, while the rest of Gemini is made up of several lines of stars extending roughly from Castor and Pollux in the general direction of Betelgeux.

In mythology, the Twins were heroes, sons of the Spartan king Tyndarus and his queen Leda. Many legends are associated with them, and they are said to have taken part in Jason's expedition to obtain the Golden Fleece. Pollux was immortal, while Castor was not. When the inevitable happened, and Castor was killed, Pollux was so heartbroken that he was allowed to share his immortality with his brother, so that both were placed in the heavens. It is worth noting, incidentally, that while Pollux is now appreciably the brighter of the two, Ptolemy ranked it inferior to Castor, so that it has been suggested that Castor has faded appre­ciably during the past 2,000 years.

Jason's ship, the Argo, is also to be found in the sky, but unfortu­nately it lies so far south that little of it rises in Britain. Its leading star, Canopus, is the brightest star in the heavens apart from Sirius, but it can never be seen in our latitudes, and only just rises above the horizon in Ptolemy's home-town of Alexandria. Argo is so huge that it has been convenient to divide it into several parts, of which the most important are Carina (the Keel), Vela (the Sails) and Puppis (the Poop).

Another of Ptolemy's original groups is Auriga, the Charioteer or Wagoner. It is marked by one particularly bright star, the yellow Capella, which is almost overhead in Britain during winter evenings, so occupying the zenith position taken during summer evenings by the equally bright, bluish Vega. Close to Capella are three fainter stars arranged in a triangle, known collectively as the Haedi or Kids. Epsilon Aurigae, at the apex of the triangle, is an exceptionally interesting object; it is a binary, and the fainter component is the largest star known, since its diameter is about 2,000,000,000 miles. Epsilon Aurigae is more than 3,000 light-years distant, whereas Capella, at only forty-five light-years, is relatively close to us.

The mythological Auriga was Erechthonius, son of Vulcan, the Olympian blacksmith. Erechthonius was born deformed, and was reared by Minerva without the knowledge of the other gods. When he reached manhood he became King of Athens, and invented the four-horse chariot, for which Jupiter rewarded him by placing him in the sky.

Turning now to the northern groups, we must say something about the two Bears, Ursa Major and Ursa Minor. The famous pattern of seven stars making up the Plough is only part of Ursa Major, though the rest of the constellation is inconspicuous; Ursa Minor contains the Pole Star, Polaris, which is highly luminous and which lies at a distance of nearly 700 light-years.

Ursa Major was originally Callisto, attendant to the goddess Juno and daughter of King Lycaon of Arcadia. Her beauty sur­passed Juno's own, and the jealous goddess was enraged as a result. To protect Callisto, Jupiter changed her into a bear. Unfortunately Gallisto's son, Areas, saw the bear while he was out hunting, and was about to kill it with his spear when Jupiter intervened, turning Areas into a bear also and placing both animals among the stars.

Most celebrated of all, perhaps, is the legend of how Perseus killed the terrible Gorgon, Medusa, and then rescued the princess Andromeda from a sea-monster. All the characters are to be found in the sky; Perseus and the Gorgon's head are there, together with Andromeda and her royal parents, Cepheus and Cassiopeia, while the sea-monster (Cetus) sprawls down toward the southern horizon Constellations added since the days of Ptolemy have no legends attached to them; such are the Lizard (Lacerta), the Little Lion (Leo Minor) and even the famous Southern Cross. However, other 'modern' groups, such as Phoenix (the Phoenix) retain mytho­logical associations.

From time to time it has been suggested that the constellations should be drastically revised, the old figures being abandoned in favour of some easily-remembered and convenient system. Yet the present groupings have been in use for so long that to alter them would mean immense work and inconvenience, since all star-maps and catalogues would have to be amended, and to engage in such a task seems to be pointless. At this stage it would not even be desirable to reject the smallest and least distinctive constellations, such as Leo Minor, which contain no bright stars or important objects, and which really have no claim to separate identity.

Apart from this, it would be a great pity to throw tradition over­board. Though astronomy has long since become an exact science, it still retains its aura of mystery, and the old legends are too fascinating to be forgotten.