Chapter 2
Greek cosmology
The rst cosmologies" were based on creation myths in which one or
more deities made the universe out of sheer will, or out of their bodily
uids, or of the carcass of some god they defeated, etc. A few examples
of such heories" of the universe are provided in this chapter. These are
hardly scientic theories in the sense that they have almost no support form
observation and in that they predict very few things outside of the fact that
there is a world (if everything is due to the whims of the Gods then there
is very little one can predict). It is an interesting comment on the workings
of the human mind that quite dierent cultures produced similar creation
myths.
The rst scientic cosmology was created by the Greeks more than 2000
years ago, and this chapter also describes these ideas and their origin. The
Greeks used some of the knowledge accumulated by earlier civilizations,
thus this chapter begins with a brief description of the achievements of
the Egyptians and Babylonians. We then consider the highlights of Greek
cosmology culminating with Ptolemy's system of the world.
2.1 Egypt and Babylon
2.1.1 Babylon
The Babylonians lived in Mesopotamia, a fertile plain between the Tigris
and Euphrates rivers (see Fig. 2.1). They developed an abstract form of
writing based on cuneiform (wedge-shaped) symbols. Their symbols were
written on wet clay tablets which were baked in the sun; many thousands
of these tablets have survived to this day; an example is shown in Fig. 2.1.
1
2
Figure 2.1: Left: Region dominated by the Babylonian civilization. Right:
example of a cuneiform tablet containing Pythagorean triples.
The Babylonian apparently believed the Earth to be a big circular plane
surrounded by a river beyond which lies an impassable mountain barrier,
with the whole thing resting on a cosmic sea. No human may cross the river
surrounding the Earth. The mountains support the vault of heaven, which
is made of a very strong metal. There is a tunnel in the northern mountains
that opens to the outer space and which also connects two doors, one in the
East and one in the West. The sun comes out through the eastern door,
travels below the metallic heavens and then exits through the western door;
he spends the nights in the tunnel.
The creation myth is more lively than the Egyptian version. It imagines
that the cosmic ocean Apsu mixed with chaos Tiamat and eventually generated
life. For a while life was good for the gods but there came a time when
Tiamat felt her domain was too small and made war against the other gods.
All but Marduk were afraid of her, so Marduk, after getting all the powers
from the frightened gods, fought Tiamat. When Tiamat opened her mouth
to swallow him he thrust a bag full with hurricane winds into her so that
she swelled and, taking advantage of her indisposition, Marduk pierced her
with his lance and killed her. Then he split Tiamat's carcass making the
lower half the earth and the upper the heavens. Finally Marduk mixed his
bloodown blood with the earth to make men for the service of the gods.
Babylonians and Chaldeans observed the motion of the stars and planets
from the earliest antiquity (since the middle of the 23rd century B.C.). They
cataloged the motion of the stars and planets as well as the occurrence of
eclipses and attempted to t their behavior to some numerical theories.
Many of these observations were used for astrological prophesying and, in
fact, they were the originators of astrology. They believed that the motions
3
and changes in the stars and planets determine (or so they believed) what
occurs on this planet.
The Babylonians excelled in computational mathematics, they were able
to solve algebraic equations of the rst degree, understood the concept of
function and realized the truth of Pythagoras' theorem (without furnishing
an abstract proof). One of the clay tablets dated from between 1900 and
1600 B.C. contains answers to a problem containing Pythagorean triples, i.e.
numbers a; b; c with a2 + b2 = c2. It is said to be the oldest number theory
document in existence. The Babylonians had an advanced number system
with base 60 rather than the base 10 of common today. The Babylonians
divided the day into 24 hours, each hour into 60 minutes, each minute into
60 seconds. This form of counting has survived for 40 centuries.
2.1.2 Egypt
The anciebloodnt Egyptians conceived the sky as a roof placed over the
world supported by columns placed at the four cardinal points. The Earth
was a
at rectangle, longer from north to south, whose surface bulges slightly
and having (of course) the Nile as its center. On the south there was a river
in the sky supported by mountains and on this river the sun god made his
daily trip (this river was wide enough to allow the sun to vary its path as it
is seen to do). The stars were suspended from the heavens by strong cables,
but no apparent explanation was given for their movements.
There is no unique Egyptian creation myth, yet one of the most colorful
versions states that at the beginning of the world,Nuit, the goddess of the
night, was in a tight embrace with her husband Sib^u, the earth god. Then
one day, without an obvious reason, the god Sh^u grabed her and elevated her
to the sky (to become the sky) despite the protests and painful squirmings
of Sib^u. But Sh^u has no sympathy for him and freezes Sib^u even as he is
thrashing about. And so he remains to this day, his twisted pose generating
the irregularities we see on the Earth's surface (see Fig. 2.2). Nuit is supported
by her arms and legs which become the columns holding the sky. The
newly created world was divided into four regions or houses, each dominated
by a god. Since the day of creation Sib^u has been clothed in verdure and
generations of animals prospered on his back, but his pain persists.
An extended version of this myth imagines that in the beginning the
god Tumu suddenly cried Come to me!" across the cosmic ocean, whence a
giant lotus
ower appeared which had the god Ra inside, then Ra separates
Nuit and Sib^u, and the story proceeds as above. It is noteworthy that
creation did not come through muscular eort, but through Tumu's voiced
4
Figure 2.2: Nuit the sky above Sib^u the Earth after being separated by Sh^u
in a version of the Egyptian creation myth.
command. This later evolved into the belief that the creator made the world
with a single word, then with a single sound (yet the creation through pure
thought was not considered).
After creation the gods, especially Thot (Fig. 2.3), teach the arts and
sciences to the Egyptians. In particular Thot taught the Egyptians how
to observe the heavens and the manner in which the planets and the sun
move, as well as the names of the (36) constellations (though he apparently
neglected to tell them about eclipses which are never referred to).
Figure 2.3: The Egyptian god Thot.
The study of the heavens was not made for altruistic purposes but with
very practical aims: a good calendar was necessary in order to prepare
for the regular
ooding of the Nile as well as for religious purposes. The
Egyptian calendar had a year of precisely 365 days and was used for many
centuries; curiously they never corrected for the fact that the year is 365
Chapter 2Greek cosmologyThe rst cosmologies" were based on creation myths in which one ormore deities made the universe out of sheer will, or out of their bodilyuids, or of the carcass of some god they defeated, etc. A few examplesof such heories" of the universe are provided in this chapter. These arehardly scienti c theories in the sense that they have almost no support formobservation and in that they predict very few things outside of the fact thatthere is a world (if everything is due to the whims of the Gods then thereis very little one can predict). It is an interesting comment on the workingsof the human mind that quite di erent cultures produced similar creationmyths.The rst scienti c cosmology was created by the Greeks more than 2000years ago, and this chapter also describes these ideas and their origin. TheGreeks used some of the knowledge accumulated by earlier civilizations,thus this chapter begins with a brief description of the achievements ofthe Egyptians and Babylonians. We then consider the highlights of Greekcosmology culminating with Ptolemy's system of the world.2.1 Egypt and Babylon2.1.1 BabylonThe Babylonians lived in Mesopotamia, a fertile plain between the Tigrisand Euphrates rivers (see Fig. 2.1). They developed an abstract form ofwriting based on cuneiform (wedge-shaped) symbols. Their symbols werewritten on wet clay tablets which were baked in the sun; many thousandsof these tablets have survived to this day; an example is shown in Fig. 2.1.12Figure 2.1: Left: Region dominated by the Babylonian civilization. Right:example of a cuneiform tablet containing Pythagorean triples.The Babylonian apparently believed the Earth to be a big circular planesurrounded by a river beyond which lies an impassable mountain barrier,with the whole thing resting on a cosmic sea. No human may cross the riversurrounding the Earth. The mountains support the vault of heaven, whichis made of a very strong metal. There is a tunnel in the northern mountainsthat opens to the outer space and which also connects two doors, one in theEast and one in the West. The sun comes out through the eastern door,travels below the metallic heavens and then exits through the western door;he spends the nights in the tunnel.The creation myth is more lively than the Egyptian version. It imaginesthat the cosmic ocean Apsu mixed with chaos Tiamat and eventually generatedlife. For a while life was good for the gods but there came a time whenTiamat felt her domain was too small and made war against the other gods.All but Marduk were afraid of her, so Marduk, after getting all the powersfrom the frightened gods, fought Tiamat. When Tiamat opened her mouthto swallow him he thrust a bag full with hurricane winds into her so thatshe swelled and, taking advantage of her indisposition, Marduk pierced herwith his lance and killed her. Then he split Tiamat's carcass making thelower half the earth and the upper the heavens. Finally Marduk mixed hisbloodown blood with the earth to make men for the service of the gods.Babylonians and Chaldeans observed the motion of the stars and planetsfrom the earliest antiquity (since the middle of the 23rd century B.C.). Theycataloged the motion of the stars and planets as well as the occurrence ofeclipses and attempted to t their behavior to some numerical theories.Many of these observations were used for astrological prophesying and, infact, they were the originators of astrology. They believed that the motions3and changes in the stars and planets determine (or so they believed) whatoccurs on this planet.The Babylonians excelled in computational mathematics, they were ableto solve algebraic equations of the rst degree, understood the concept offunction and realized the truth of Pythagoras' theorem (without furnishingan abstract proof). One of the clay tablets dated from between 1900 and1600 B.C. contains answers to a problem containing Pythagorean triples, i.e.numbers a; b; c with a2 + b2 = c2. It is said to be the oldest number theorydocument in existence. The Babylonians had an advanced number systemwith base 60 rather than the base 10 of common today. The Babyloniansdivided the day into 24 hours, each hour into 60 minutes, each minute into60 seconds. This form of counting has survived for 40 centuries.2.1.2 EgyptThe anciebloodnt Egyptians conceived the sky as a roof placed over theworld supported by columns placed at the four cardinal points. The Earthwas a at rectangle, longer from north to south, whose surface bulges slightlyand having (of course) the Nile as its center. On the south there was a riverin the sky supported by mountains and on this river the sun god made hisdaily trip (this river was wide enough to allow the sun to vary its path as itis seen to do). The stars were suspended from the heavens by strong cables,but no apparent explanation was given for their movements.There is no unique Egyptian creation myth, yet one of the most colorfulversions states that at the beginning of the world,Nuit, the goddess of thenight, was in a tight embrace with her husband Sib^u, the earth god. Thenone day, without an obvious reason, the god Sh^u grabed her and elevated herto the sky (to become the sky) despite the protests and painful squirmingsof Sib^u. But Sh^u has no sympathy for him and freezes Sib^u even as he isthrashing about. And so he remains to this day, his twisted pose generatingthe irregularities we see on the Earth's surface (see Fig. 2.2). Nuit is supportedby her arms and legs which become the columns holding the sky. Thenewly created world was divided into four regions or houses, each dominatedby a god. Since the day of creation Sib^u has been clothed in verdure andgenerations of animals prospered on his back, but his pain persists.An extended version of this myth imagines that in the beginning thegod Tumu suddenly cried Come to me!" across the cosmic ocean, whence agiant lotus ower appeared which had the god Ra inside, then Ra separatesNuit and Sib^u, and the story proceeds as above. It is noteworthy thatcreation did not come through muscular e ort, but through Tumu's voiced4Figure 2.2: Nuit the sky above Sib^u the Earth after being separated by Sh^uin a version of the Egyptian creation myth.command. This later evolved into the belief that the creator made the worldwith a single word, then with a single sound (yet the creation through purethought was not considered).After creation the gods, especially Thot (Fig. 2.3), teach the arts andsciences to the Egyptians. In particular Thot taught the Egyptians howto observe the heavens and the manner in which the planets and the sunmove, as well as the names of the (36) constellations (though he apparentlyneglected to tell them about eclipses which are never referred to).Figure 2.3: The Egyptian god Thot.The study of the heavens was not made for altruistic purposes but withvery practical aims: a good calendar was necessary in order to preparefor the regular ooding of the Nile as well as for religious purposes. TheEgyptian calendar had a year of precisely 365 days and was used for manycenturies; curiously they never corrected for the fact that the year is 365
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Chapter 2
Greek cosmology
The rst cosmologies" were based on creation myths in which one or
more deities made the universe out of sheer will, or out of their bodily
uids, or of the carcass of some god they defeated, etc. A few examples
of such heories" of the universe are provided in this chapter. These are
hardly scientic theories in the sense that they have almost no support form
observation and in that they predict very few things outside of the fact that
there is a world (if everything is due to the whims of the Gods then there
is very little one can predict). It is an interesting comment on the workings
of the human mind that quite dierent cultures produced similar creation
myths.
The rst scientic cosmology was created by the Greeks more than 2000
years ago, and this chapter also describes these ideas and their origin. The
Greeks used some of the knowledge accumulated by earlier civilizations,
thus this chapter begins with a brief description of the achievements of
the Egyptians and Babylonians. We then consider the highlights of Greek
cosmology culminating with Ptolemy's system of the world.
2.1 Egypt and Babylon
2.1.1 Babylon
The Babylonians lived in Mesopotamia, a fertile plain between the Tigris
and Euphrates rivers (see Fig. 2.1). They developed an abstract form of
writing based on cuneiform (wedge-shaped) symbols. Their symbols were
written on wet clay tablets which were baked in the sun; many thousands
of these tablets have survived to this day; an example is shown in Fig. 2.1.
1
2
Figure 2.1: Left: Region dominated by the Babylonian civilization. Right:
example of a cuneiform tablet containing Pythagorean triples.
The Babylonian apparently believed the Earth to be a big circular plane
surrounded by a river beyond which lies an impassable mountain barrier,
with the whole thing resting on a cosmic sea. No human may cross the river
surrounding the Earth. The mountains support the vault of heaven, which
is made of a very strong metal. There is a tunnel in the northern mountains
that opens to the outer space and which also connects two doors, one in the
East and one in the West. The sun comes out through the eastern door,
travels below the metallic heavens and then exits through the western door;
he spends the nights in the tunnel.
The creation myth is more lively than the Egyptian version. It imagines
that the cosmic ocean Apsu mixed with chaos Tiamat and eventually generated
life. For a while life was good for the gods but there came a time when
Tiamat felt her domain was too small and made war against the other gods.
All but Marduk were afraid of her, so Marduk, after getting all the powers
from the frightened gods, fought Tiamat. When Tiamat opened her mouth
to swallow him he thrust a bag full with hurricane winds into her so that
she swelled and, taking advantage of her indisposition, Marduk pierced her
with his lance and killed her. Then he split Tiamat's carcass making the
lower half the earth and the upper the heavens. Finally Marduk mixed his
bloodown blood with the earth to make men for the service of the gods.
Babylonians and Chaldeans observed the motion of the stars and planets
from the earliest antiquity (since the middle of the 23rd century B.C.). They
cataloged the motion of the stars and planets as well as the occurrence of
eclipses and attempted to t their behavior to some numerical theories.
Many of these observations were used for astrological prophesying and, in
fact, they were the originators of astrology. They believed that the motions
3
and changes in the stars and planets determine (or so they believed) what
occurs on this planet.
The Babylonians excelled in computational mathematics, they were able
to solve algebraic equations of the rst degree, understood the concept of
function and realized the truth of Pythagoras' theorem (without furnishing
an abstract proof). One of the clay tablets dated from between 1900 and
1600 B.C. contains answers to a problem containing Pythagorean triples, i.e.
numbers a; b; c with a2 + b2 = c2. It is said to be the oldest number theory
document in existence. The Babylonians had an advanced number system
with base 60 rather than the base 10 of common today. The Babylonians
divided the day into 24 hours, each hour into 60 minutes, each minute into
60 seconds. This form of counting has survived for 40 centuries.
2.1.2 Egypt
The anciebloodnt Egyptians conceived the sky as a roof placed over the
world supported by columns placed at the four cardinal points. The Earth
was a
at rectangle, longer from north to south, whose surface bulges slightly
and having (of course) the Nile as its center. On the south there was a river
in the sky supported by mountains and on this river the sun god made his
daily trip (this river was wide enough to allow the sun to vary its path as it
is seen to do). The stars were suspended from the heavens by strong cables,
but no apparent explanation was given for their movements.
There is no unique Egyptian creation myth, yet one of the most colorful
versions states that at the beginning of the world,Nuit, the goddess of the
night, was in a tight embrace with her husband Sib^u, the earth god. Then
one day, without an obvious reason, the god Sh^u grabed her and elevated her
to the sky (to become the sky) despite the protests and painful squirmings
of Sib^u. But Sh^u has no sympathy for him and freezes Sib^u even as he is
thrashing about. And so he remains to this day, his twisted pose generating
the irregularities we see on the Earth's surface (see Fig. 2.2). Nuit is supported
by her arms and legs which become the columns holding the sky. The
newly created world was divided into four regions or houses, each dominated
by a god. Since the day of creation Sib^u has been clothed in verdure and
generations of animals prospered on his back, but his pain persists.
An extended version of this myth imagines that in the beginning the
god Tumu suddenly cried Come to me!" across the cosmic ocean, whence a
giant lotus
ower appeared which had the god Ra inside, then Ra separates
Nuit and Sib^u, and the story proceeds as above. It is noteworthy that
creation did not come through muscular eort, but through Tumu's voiced
4
Figure 2.2: Nuit the sky above Sib^u the Earth after being separated by Sh^u
in a version of the Egyptian creation myth.
command. This later evolved into the belief that the creator made the world
with a single word, then with a single sound (yet the creation through pure
thought was not considered).
After creation the gods, especially Thot (Fig. 2.3), teach the arts and
sciences to the Egyptians. In particular Thot taught the Egyptians how
to observe the heavens and the manner in which the planets and the sun
move, as well as the names of the (36) constellations (though he apparently
neglected to tell them about eclipses which are never referred to).
Figure 2.3: The Egyptian god Thot.
The study of the heavens was not made for altruistic purposes but with
very practical aims: a good calendar was necessary in order to prepare
for the regular
ooding of the Nile as well as for religious purposes. The
Egyptian calendar had a year of precisely 365 days and was used for many
centuries; curiously they never corrected for the fact that the year is 365
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