CHAPTER ONE continued...
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
around 1000 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.
Professor Archie Roy of Glasgow University
has argued that the Babylonian constellations reached Egypt
(and hence Eudoxus) via some other civilization; he proposes
that they 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
around 1700 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.
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.
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.
After Aratus, the next landmark in our
study of Greek constellation lore is Eratosthenes
(c.276–c.194 BC), to whom an essay called the Catasterisms is
attributed. Eratosthenes was a Greek scientist and writer who
worked in Alexandria at the mouth of the Nile. The Catasterisms gives the
mythology of 42 separate constellations (the Pleiades cluster
is treated individually), with a listing of the main stars in
each figure. The version of the Catasterisms that survives is only a summary of the original,
made at some unknown date, and it is not even certain that the
original was written by the real Eratosthenes; hence the author
of the Catasterisms is usually referred to as pseudo-Eratosthenes.
The antiquity of his sources is certain, though, because he
quotes in places from a long-lost work on astronomy by Hesiod
(c.700 BC).
Another influential source of constellation
mythology is a book called Poetic
Astronomy by a Roman author named
Hyginus, apparently written in the second century AD. We do not know who
Hyginus was, not even his full name – he was evidently
not C. Julius Hyginus, a Roman writer of the first century BC. Poetic Astronomy is based on
the constellations listed by Eratosthenes (Hyginus differs only
by including the Pleiades under Taurus), but it contains many
additional stories. Hyginus also wrote a compendium of general
mythology called the Fabulae. In medieval and Renaissance times many
illustrated versions of Hyginus’s writings on astronomy
were produced.
Marcus Manilius, a Roman author of whom
virtually nothing is known, wrote a book called Astronomica around the
year AD
15, clearly influenced by the Phaenomena of Aratus. Manilius’s book deals
mostly with astrology rather than astronomy, but it contains
numerous insights into constellation lore and I have quoted him
a number of times.
The names of three other mythologists
appear frequently on the following pages, and although they are
not astronomers they must be introduced before we return to the
history of the constellations. Foremost among them is the Roman
poet Ovid (43 BC–AD 17), who recounts many famous myths in his books the Metamorphoses, which
deals with transformations of all kinds, and the Fasti, a treatise on
the Roman calendar. Apollodorus was a Greek who compiled an
almost encyclopedic summary of myths known as the Library some time in
the late first century BC or in the first century AD. Finally there is the
Greek writer Apollonius Rhodius (Apollonius of Rhodes) whose Argonautica, an epic
poem on the voyage of Jason and the Argonauts composed in the
third century BC, includes much mythological information. These are the
main sources for the stories in this book.
Greek astronomy reached its pinnacle with
Ptolemy (c.AD 100–c.178) who worked in Alexandria, Egypt.
Around AD
150, Ptolemy produced a summary of Greek astronomical knowledge
usually known by its later Arabic title of the Almagest. At its heart
was a catalogue of 1022 stars arranged into 48 constellations
(see Table 1), with estimates of their brightness, based
largely on the observations of the Greek astronomer Hipparchus
three centuries earlier.
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Ptolemy did not identify the stars in his
catalogue by means of Greek letters, as astronomers do today,
but described their position within each constellation figure.
For instance, the star in Taurus which Ptolemy referred to as
“the reddish one on the southern eye” is known
today as Aldebaran. At times, this system became cumbersome:
“The northernmost of the two stars close together over
the little shield in the poop” is how Ptolemy struggled
to identify a star (now called Xi Puppis) in the obsolete
constellation of Argo.
The tradition of describing stars by their
positions within a constellation had already been established
by Eratosthenes and Hipparchus. Clearly, the Greeks regarded
the constellations not merely as assemblages of stars but as
true pictures in the sky. Identification would have been easier
if they had given the stars individual names, but Ptolemy added
only four stars to those named by Aratus four centuries earlier:
Altair (which Ptolemy called Aetus, meaning eagle); Antares;
Regulus (which he called Basiliscus); and Vega (which he called
Lyra, the same name as its constellation).
It would be difficult to overemphasize the
influence of Ptolemy on astronomy; the constellation system we
use today is essentially Ptolemy’s, modified and
extended. Mapmakers in Europe and Arabia used his constellation
figures for over 1500 years, witness this passage from the
preface to the Atlas Coelestis by the first Astronomer Royal, John
Flamsteed, published in 1729:
“From Ptolemy’s time to ours
the names that he made use of have been continued by the
ingenious and learned men of all nations; the Arabians always
used his forms and names of the constellations; the old Latin
catalogues of the fixed stars use the same; Copernicus’s
catalogue and Tycho Brahe’s use the same; so do the
catalogues published in the German, Italian, Spanish,
Portuguese, French and English languages. All the observations
of the ancients and moderns make use of Ptolemy’s forms
of the constellations and names of the stars so that there is a
necessity of adhering to them, that we may not render the old
observations unintelligible by altering or departing from
them.”
After Ptolemy, Greek astronomy went into
permanent eclipse. By the eighth century AD the centre of astronomy
had moved east from Alexandria to Baghdad where Ptolemy’s
work was translated into Arabic and received the name Almagest by which we
still know it. Al-Sufi (AD 903–86), one of the greatest Arabic
astronomers (also known by the Latinized name of Azophi),
produced his own version of the Almagest called the Book of
the Fixed Stars in which he
introduced many star names.
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From the tenth century onwards, the works
of Ptolemy were reintroduced into Europe by Islamic Arab
incursions and the Greek books were translated from Arabic into
Latin, the scientific language of the day. Through this
roundabout route we have ended up with a polyglot system of
Greek constellations with Latin names containing stars with
Arabic titles.
© Ian Ridpath. All rights reserved