Transcript The Egyptians through the Romans

The Egyptians through the Greeks
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The Practical Sky
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Probably before there was civilization there was a
need to keep track of days
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Migration of prey animals
Rutting season for domesticated animals
Agriculture: planting and harvesting (8000 years ago)
The phases of the Moon, the rising position of the
Sun, and prominent constellations provided clues
for the time of year
Timeline
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Dates in some cases are approximate; some
civilizations achieved various milestones at later
times. The dates cited are generally the earliest
verifiable dates.
Prehistoric Civilizations
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Clockwise from top: Varna 4400BC, Mesopotamia 3100 BC, Tell
Hamoukar 4000BC, Tell Qaramel 9600 BC, Minos 2700 BC
Dangers in Interpreting Ancient
Structures
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We must take care not to
superimpose our
understanding of the sky
onto ancient builders
One way to avoid this
error is to look at many
supposedly astronomically
inspired structures
Why do you think the
preferred orientation is
slightly south of east?
Orientation of Late Stone Age communal
tombs on the Iberian peninsula.
M. Hoskins
Egyptian Astronomers
• Constructed by
nomadic cattle herders
• ~ 7000 years old
• Covers an area of 2.9
km by 1.2 km
• 10 slabs about 2.7
meters high, bovine
burial mounds, and a
calendar circle
Goseck Circle
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Oldest Solar
Observatory
Discovered in Germany
2002
Bronze Age (7000
years ago)
Reconstructions on
upper, middle right
Nebra disk (bottom)
found nearby but not
nearly so old
Sumerian Planosphere
Stonehenge
Solstice Sunrise at Stonehenge
Carhenge (not so ancient)
Babylon
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Ziggurat (Ur, Iraq; 2000 BCE)
Celestial Observatory and temple
Cuneiform citing lunar eclipse
Centuries of recorded
planetary observations
Thirteen Towers of Chankillo
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Peru, 2300 years old
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Towers stand 6 to 13 feet, extending 1,00 feet
away, marking positions of the Sun over a year
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Oldest Solar Observatory in the Americas
From central position the arc of the rising Sun is
subtended
Ceremonial buildings in the rings
Observers stood here
Mayan Observatories circa 900 AD
El Caracol
Chichen Itza
The Antikythera
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An instrument, not an
observatory
1st Century BCE
Named for the Greek
island near the
shipwreck from which
this was discovered,
circa 1900
A mechanical
computer for celestial
positions
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Similar to Byzantine sundial
calendar, 500 AD
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Perhaps made by Archimedes of
Syracuse, Sicily
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Known for great inventions
Between 29 and 70 gears wheels
for more complicated calculations
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But this is much simpler
(some gears missing)
Tower of the Winds in Athens
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Sebius water clock inside
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Egyptian inventor
Antikythera mechanism
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A computer for horoscopes
Perhaps every town had a tower, a
water clock, and a mechanism
The Greeks: First Millennium BCE
Greek Reason
• Thales ~700BCE
– Lodestone
– Amber
• Anaximander ~ 650 BCE
– Attempted to describe the
mechanics of celestial bodies
• Socrates ~400 BCE
– “The Cave”
– We see reality as shadows on
the cave wall
• Plato: student of Socrates
Plato’s Republic: The Myth of Er
• Er was a character in
Republic
• Whorl (spindle) Of
Necessity
• Celestial Spheres
Eudoxus of Cnidus ( 408-355 BCE)
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Colleague of Plato
Originator of scientific
astronomy
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No works survive
Envisioned a system of
20 concentric spheres
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Spheres because of
their symmetry and
unity
Earth centermost
Rotational axis fixed to
next largest sphere
Introduction of epicycles
First Principles
To account for:
stability in the
world.
find what is fundamental, constant
and unchanging..
diversity in the
world.
find what is different, what changes,
and how it changes; this will reveal
the rules or agencies that control
the change process.
use these rules to organize the
fundamentals into a "neat
array".
pattern in the
world..
which the
Greeks called:
arché
physis
cosmos
Timeaus:
• 2 Circles Split
• Circle of the Same
– Celestial Equator
• Circle of the Different
– Ecliptic
Quadrivium: Greek Learning
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Arithmetic:
Geometry:
Music:
Astronomy:
number
number in space
number in time
number in motion
Five Perfect Solids (Things to come)
Terrestrial Elements
Qualities
Earth
Cold and Dry
Water
Cold and Wet
Air
Warm and Wet
Fire
Warm and Dry
Celestial Element
Quintessence, or aether
quintessence is perfect and
immutable
Aristotle 384-322 BCE
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Student at Plato’s Academy / Teacher for
Alexander
Each terrestrial element (earth, water, air,
fire) has a natural place or state; some
amount of each element is present in every
body
Gravity/Levity
If a body (animate or inanimate) is removed
from the natural place or state of its
predominant element (violent change), it will
naturally strive to return where it belongs
(natural change)
physis
Metaphysics
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For Aristotle, his “First Philosophy”, coming after
physis
For us, the study and doctrine of internal, active
principles in things
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Intrinsic properties or qualities
Examples
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The intrinsic nature of rock is ‘heavy’, and it seeks the
center of the Earth
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The intrinsic nature of fire is ‘not heavy’ and it reaches
upward
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NOT that Earth’s mass pulls it down
NOT that convection currents steer the flames
Not until the 17th century will these ideas be
challenged
Influence felt for almost 2000 years
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Adopts (and adapts) Eudoxus’ spherical model
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Geocentrism
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Not a mathematician
Simplifies model
Calls the outermost sphere the “Prime Mover”
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Earth at the center because it’s heavy
And spherical (!) contrary to myths of a flat world
Remember, each axis fixed to the next outer sphere
Adopted later by the Roman Church as God
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Earth where man lives
The Underworld of fire and brimstone
The Hellenistic Era
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The time right after the death of Alexander
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323 - 31 BCE, when Rome emerges
Commerce flourishes
Greek culture had been spread over a wide area
Museum at Alexandria: 400,000 scrolls
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Center of learning for hundreds of years
Burned by zealots in 415 AD
Librarian and Philosopher Hypatia killed for heresy
The Hellenistic World
Aristarchos 310-230 BCE
• Had a different cosmological view than Aristotle:
Heliocentrism
• Found the ratio of the Earth to Moon diameter
Erastosthenes
276 - 194 BCE
• Determined the
size of the
Earth, the
distance to the
Moon, and the
size of the
Moon, all very
accurately.
Apollonius of Perga 190 – 120 BCE
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Mathematician
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Conic sections
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Math 80
Introduced eccentric
orbits
Hipparchus of Rhodes 190-120 BCE
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Precession of the equinoxes
Devised the Magnitude Scale for his catalog
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Clumsy but still in use (modified heavily) today
Then, brightest star (Sirius) = 1, dimmest = 6
Now Vega is labeled zero, brighter objects are
negative, very dim objects are 20-30
Took centuries of Babylonian observations and
tried to reconcile the data with a combination of
epicycles and eccentric orbits
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In sexigesimal!
He made it work for the moon…
Retrograde Motion
• Apparent backwards motion of planētēs in the sky
• Wanderers; not the Sun or Moon
• Difficult to reconcile with Aristotle - geocentrism
*Ptolemy (Claudius) 90-168AD
• Mathematician,
Astronomer, and
Astrologer
• Star catalog of 1000 stars
in 48 constellations
• Maybe Hipparchus’
catalog
• Tetrabiblios: Astrology
text
• Scornful of previous 3
centuries of
astronomy/astrology
*Ptolemy I was one of Alexander’s generals. He was given
governorship of Egypt by Alexander and the Ptolemys ruled
the country for centuries.
Note the cross-staff
The Mathematike Syntaxis
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“The Mathematical Compilation”
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…that the heavens are spherical and move spherically;
…that the earth, in figure, is sensibly spherical also
when taken as a whole
…[that the earth] in position, lies right in the middle
of the heavens, like a geometrical center;
…[that the earth] in magnitude and distance, has the
ratio of a point with respect to the sphere of the fixed
stars, having itself no local motion at all.
Incorporates Hipparchus’ equinox precession for
accurate for predicting planetary positions for
many centuries
Epicycles, Eccentrics, and now the
Equant
deferent
Equant point
Planetary
Hypothesis
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Ptolemy reasoned that
longer period planets are
closer to the stars, furthest
from Earth
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Saturn, Jupiter, Mars far,
Moon closest
Sun, Mercury, Venus a
problem
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Since Mercury and Venus
are solar companions, he
put the Sun nearer than
Mars, then Venus and
Mercury with little
evidence
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Distances:
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Moon: 64 Rearth
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~256,000 miles; 
Stars: 19,865 Rearth
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~ 75 million miles 