Ian Ridpath’s Star TalesCHAPTER ONE
Stars and storytellers
Every night, a pageant of Greek mythology circles overhead. Perseus flies to the rescue of Andromeda, Orion faces the charge of the snorting bull, Boötes herds the bears around the pole, and the ship of the Argonauts sails in search of the golden fleece. These legends, along with many others, are depicted in the star patterns that astronomers term constellations.
Constellations are the invention of human imagination, not of nature. They are an expression of the human desire to impress its own order upon the apparent chaos of the night sky. For navigators beyond sight of land or for travellers in the trackless desert who wanted signposts, for farmers who wanted a calendar and for shepherds who wanted a nightly clock, the division of the sky into recognizable star groupings had practical purposes. But perhaps the earliest motivation was to humanize the forbidding blackness of night.
Newcomers to astronomy are soon disappointed to find that the great majority of constellations bear little, if any, resemblance to the figures whose names they carry; but to expect such a resemblance is to misunderstand their true meaning. The constellation figures are not intended to be taken literally. Rather, they are symbolic, a celestial allegory. The night sky was a screen on which human imagination could project the deeds and personifications of deities, sacred animals and moral tales. It was a picture book in the days before writing.
Each evening the stars emerge like magic spirits as the Sun descends to its nocturnal lair. Twentieth-century science has told us that those twinkling points scattered across the sky in their thousands are actually glowing balls of gas similar to our own Sun, immensely far away. A star’s brightness in the night sky is a combination of its own power output and its distance from us. So far apart are the stars that light from even the nearest of them takes many years to reach us. The human eye, detecting the faint spark from star fires, is seeing across unimaginable gulfs of both space and time.
Such facts were unknown to the ancient Greeks and their predecessors, to whom we owe the constellation patterns that we recognize today. They were not aware that, with a few exceptions, the stars of a constellation have no connection with each other, but lie at widely differing distances. Chance alone has given us such familiar shapes as the ‘W’ of Cassiopeia, the square of Pegasus, the sickle of Leo or the Southern Cross.
The constellation system that we use today has grown from a list of 48 constellations published around AD 150 by the Greek scientist Ptolemy in an influential book called the Almagest. Since then, various astronomers have added another 40 constellations, filling the gaps between Ptolemy’s figures and populating the region around the south celestial pole that was below the horizon of the Greeks. The result is a total of 88 constellations that all astronomers accept by international agreement. The tales of these constellations are told in this book – along with nearly two dozen others that fell by the wayside.
Ptolemy did not invent the constellations that he listed. They are much older than his era, although exactly when and where they were invented is lost in the mists of time. The early Greek writers Homer and Hesiod (c.700 BC) mentioned only a few star groups, such as the Great Bear, Orion, and the Pleiades star cluster (the Pleiades was then regarded as a separate constellation rather than being incorporated in Taurus as it is today).
The major developments evidently took place farther east, around the Tigris and Euphrates rivers in what is now Iraq. There lived the Babylonians, who at the time of Homer and Hesiod had a well-established system of constellations of the zodiac, the strip of sky traversed by the Sun, Moon and planets. We know this from a star list written in cuneiform on a clay tablet dated to around 700 BC. Scholars call this list the mul-Apin series, from the first name recorded on the tablet. The Babylonian constellations had many similarities with those we know today, but they are not all identical. From other texts, historians have established that the constellations known to the Babylonians actually originated much earlier, with their ancestors the Sumerians before 2000 BC.
If the Greeks of Homer and Hesiod’s day knew of the Babylonian zodiac they did not write about it. The first clear evidence we have for an extensive set of Greek constellations comes from the astronomer Eudoxus (c.390–c.340 BC). Eudoxus reputedly learned the constellations from priests in Egypt and introduced them to Greece, which makes his contribution to astronomy highly significant. He published descriptions of the constellations in two works called Enoptron (Mirror) and Phaenomena (Appearances). Both these works are lost, but the Phaenomena lives on in a poem of the same name by another Greek, Aratus (c.315–c.245 BC). Aratus’s Phaenomena gives us a complete guide to the constellations known to the ancient Greeks; hence he is a major figure in our study of constellation lore.
Aratus was born at Soli in Cilicia, on the southern coast of what is now Turkey. He studied in Athens before going to the court of King Antigonus of Macedonia in northern Greece. There, at the king’s request, he produced his poetic version of the Phaenomena of Eudoxus around 275 BC. In the Phaenomena Aratus identified 47 constellations, including the Water (now regarded as part of Aquarius) and the Pleiades. Aratus also named six individual stars: Arcturus, Capella (which he called Aix), Sirius, Procyon (which formed a constellation on its own), Spica (which he called Stachys) and Vindemiatrix (which he called Protrygeter). This last star is a surprise, since it is so much fainter than the others, but the Greeks used it as a calendar star because its rising at dawn in August marked the start of the grape harvest.
Neither the Greeks nor the Egyptians actually invented the constellations that are described in the Phaenomena. The evidence for that statement lies not just in written records, but in the sky itself.
Surprisingly, it is not too difficult to work out roughly where and when the constellations known to Eudoxus and Aratus were invented. The clue is that Aratus described no constellations around the south celestial pole, for the reason that this area of sky was permanently below the horizon of the constellation makers. Since the constellation-free zone has a radius of about 36 degrees, the constellation makers must have lived at a latitude of about 36 degrees north – that is, south of Greece but north of Egypt.
A second clue comes from the fact that the constellation-free zone is centred not on the south celestial pole at the time of Aratus but on its position over 1500 years before him, at a date of about 2000 BC. (The position of the celestial pole changes slowly with time because of a wobble of the Earth on its axis, an effect known as precession.) Therefore we can conclude that the constellations described by Aratus were invented around 2000 BC by people who lived close to latitude 36 degrees north.
The 48 constellations of the Greek astronomer Ptolemy, illustrated on a pair of woodcuts made by Albrecht Dürer in 1515, one showing the northern sky (top) and the lower one the southern sky. The figures are depicted from the rear, as on a celestial globe.
Note the large blank area of the southern sky that was below the horizon to the people who invented the constellations. The size of this blank zone is a clue to the latitude at which the constellation inventors lived. (© The National Maritime Museum, London)
This date is too early for the Greeks and the latitude is too far south; Egyptian civilization is sufficiently old, but the required latitude is well north of them. The time and the place, though, ideally match the Babylonians and their Sumerian ancestors who, as we have already seen, had a well-developed knowledge of astronomy by 2000 BC. Hence two independent lines of evidence point to the Babylonians and Sumerians as the originators of our constellation system.
But why had the constellation system introduced by Eudoxus not been updated by its makers to take account of the changing position of the celestial pole? As we have seen, the constellations introduced by Eudoxus and described by Aratus in the Phaenomena refer to the position of the celestial pole over 1500 years earlier. By the time of Aratus, the shift in position of the celestial pole meant that certain stars mentioned in the Phaenomena were now permanently below the horizon from latitude 36 degrees north, while others not mentioned by Aratus had by then come into view. Oddly, Eudoxus himself seems not to have been bothered by these anomalies, if he even noticed them; but the great Greek astronomer Hipparchus (fl.146–127 BC) recognized the differences and was understandably critical.
A new twist to the tale of the constellations has been added by Professor Archie Roy of Glasgow University, who has argued that the Babylonian constellations must have reached Egypt (and hence Eudoxus) via some other civilization; he proposes that they were the Minoans of Crete. Professor Roy notes that the Phaenomena of Aratus embodies much nautical weather lore associated with the appearance of various star groups. He interprets this as evidence that the constellations were intended as a navigational aid for seamen.
Accurate knowledge of the sky would have been vital to navigators, who would set their course at night from the rising and setting points of various stars and constellations. These seafarers could have been completely different people from the constellation makers. Professor Roy concludes that the seafarers concerned were the Minoans who lived on Crete and the surrounding islands off the coast of Greece, including Thera (also known as Santorini). Crete lies between 35 and 36 degrees north, which is the right latitude, and the Minoan empire was expanding between 3000 and 2000 BC, which is the right date.
What’s more, the Minoans were in contact with the Babylonians through Syria from an early stage. Hence they must have been familiar with the old Babylonian constellations, and they could well have adapted the Babylonian star groups into a practical system for navigation.
But the Minoan civilization was wiped out in 1450 BC by the explosive eruption of a volcano on the island of Thera about 120 km north of Crete. It was one of the greatest natural catastrophes in the history of civilization, the probable origin of the legend of Atlantis. Professor Roy supposes that Minoan refugees brought their knowledge of the stars to Egypt after the eruption, where it was eventually encountered by Eudoxus in unchanged form over a thousand years later.
During the writing of this book I visited Crete. The stars seem to hang lower there; you feel that you could strip them from the sky in handfuls like grapes from a vine. The Milky Way arches overhead like a tangled skein of phosphorescent wool. As the Earth turns you cannot fail to notice stars gradually sink into the placid sea on one horizon while others emerge from the deep on the other horizon.
Professor Roy’s thesis is an attractive one, for it is easy to imagine the Minoans utilizing the Babylonian constellation system in the way that he describes. In addition, many star myths are centred on Crete. In the face of Mount Dikte overlooking the Lassithi plateau is the cave where the infant Zeus, king of the Greek gods, was reputedly reared. However, it must be admitted that there is no direct evidence, such as wall paintings or star lists like those of the Babylonians, to demonstrate any Minoan interest in astronomy. So, for now, the theory that the Minoans were middlemen to our constellation system remains nothing more than an appealing speculation.
The Phaenomena of Aratus was an immensely popular poem and was later translated several times into Latin. For our purposes the most useful version is a Latin adaptation of Aratus attributed to Germanicus Caesar (15 BC–AD 19), which has more information about the identification of certain constellations than Aratus’s original. According to the scholar D. B. Gain, this Latin version of the Phaenomena could have been written either by Germanicus himself or by his uncle (and adoptive father) Tiberius Caesar, but in this book I refer to the author simply as Germanicus.
© Ian Ridpath. All rights reserved
read more....