MESOPOTAMIAN
AND EGYPTIAN COSMOLOGY
1.
Babylonian-Egyptian Civilizations
- Stable village communities
involved in agriculture, artistic, administrative, and trade activities developed
around
- 6000 B.C. in Tigris-Euphrates
valley in fertile crescent
- 4500 B.C. in Nile
valley in Egypt
- 3000 B.C. in Indus
valley in India
- Urban centers followed
rapidly; organized for
- Agriculture and market
distribution
- Defense
- Community projects,
such as dikes, canals for irrigation
- Nile communities more
stable than fertile crescent or Indus
2.
Babylonian-Egyptian Astronomy
- Babylonians-Egyptians,
5000 years ago, identified groupings of stars, constellations
- Purpose: calendars,
navigation
- As possibly memory
aid: imagined likenesses of mythological beings or animals (asterisms)
- Greeks inherited constellations
from Babylonians-Egyptians
- Greeks identified
48 constellations
- Remaining 40 (present
88) added by Europeans
- Constellations (asterism)
today, 88 areas with north-south and east-west boundaries covering entire
sky
- Babylonians, 2000 B.C.,
recorded motions of planets
- Greeks, 1000 B.C.,
inherited Babylonian astronomical knowledge
- Greeks, developed
geometry and trigonometry, sought geometrical explanation of motions rather
than numerical relationships
- Babylonians-Egyptians
identified Sun's yearly path through constellations (ecliptic)
- Moon and planets move
along 16o-wide band, centered on ecliptic, zodiac
- Divided into 12 constellation
divisions, or signs
- Babylonians, 200 B.C.,
predicted lunar eclipses and to some extent solar eclipses
- Prediction method
derived from numerical relations (numerical algorithm) in tabulated observations
- Did not devise geometrical
relationships as did Greeks
- Size and Shape of Earth
- Earth and Moon widely
known to be spherical in Greek world by 5th century B.C.
- Aristotle (384-322
B.C.) stated such was old knowledge; probably inherited from Babylonians
and Egyptians; three arguments
- Circular shadow projected
by Earth when it eclipses Moon
- Ships disappear sailing
away from shore by sinking below horizon with mast last visible; Earth's
curvature visible over 13 mile distance
- When traveling north,
new stars appeared above northern horizon, while stars previously seen along
southern horizon no longer visible; reverse true traveling south
- Eratosthenes (273-193
B.C.) measured circumference
3.
Modern Formulation of Babylonian-Egyptian Concepts in Horizon Astronomy
- Celestial sphere
- Imaginary sphere containing
stars
- Rotates east-to-west
- Sun, Moon, Mercury,
Venus, Mars, Jupiter, Saturn move relative to background stars
- Zenith and nadir:
point directly over observer's head and under observer's feet
- Astronomical horizon:
great circle cut by plane tangent to Earth; north, east, south, west points
- Celestial meridian:
great circle running through north, zenith, south, nadir, north; divides
visible sky into rising (eastern) and setting (western)
- Celestial equator:
projection of geographic equator; great circle running from east through
west and back to east point; intersects celestial meridian at right angles
- North and south celestial
poles: intersection of Earth's axis of rotation with celestial sphere
- Diurnal (daily) motions:
rising of celestial objects above horizon, movement across sky (east to
west), and setting below horizon
- Recognized cyclic celestial
phenomena
- Sun and the seasons
- Precession of equinoxes
- Phases of Moon
- Configurations of
planets
- Lunar and solar eclipses
- Sun and the seasons
- Cause: tilt of Earth's
rotation axis by 23.5o relative to orbital plane and annual revolution
- Ecliptic: annual apparent
path of Sun on celestial sphere; inclined 23.5o to celestial equator
- Zodiac: 16o band centered
on ecliptic; Moon and planets paths; divided into 12 constellations
- Consequence: Sun moves
eastward 1o per day relative stars; stars rise 4m earlier each night, or
2h per month
- Period for annual
revolution is about 365.242d; solar year not an integral number of solar
days
- Egyptian star tables,
rising and setting
- Egyptian applied geometry
- Cardinal points on ecliptic
- Vernal equinox
- Intersection of
celestial equator and ecliptic
- Sun arrives about
March 21
- Sun rises due east
and sets due west
- 12h of daylight
and 12h of darkness
- Summer solstice
- Sun maximum distance
north of celestial equator (23.5o)
- Sun arrives about
June 21
- Sun rises far north
of east point
- Maximum hours of
daylight for northern hemisphere
- Autumnal equinox
- Second intersection
of celestial equator and ecliptic
- Sun arrives about
September 22
- Sun rises due east
and sets due west
- 12h of daylight
and 12h of darkness
- Winter solstice
- Sun maximum distance
south of celestial equator (23.5o)
- Sun arrives about
December 22
- Sun rises far south
of east point
- Minimum hours of
daylight for northern hemisphere
- Precession of equinoxes
- Precession clearly
recognized by Egyptians and Babylonians by 2nd century B.C.
- Observe that vernal
equinox shifts westward; or Earth's axis of rotation describes cone about
pole of ecliptic
- Period 25,800y or
annually 50"
- Cause: Earth's equatorial
bulge attracted gravitationally by Sun and Moon
- Consequence: north
and south celestial poles move through 47o-diameter circles on celestial
sphere every 25,800y
- Phases of the Moon
- Rotation period revolution
period
- Moves 0.5o per hour
or 13o per day relative to stars; period 27.3d for 360o revolution (sidereal
month)
- Phases: new moon,
1st quarter moon, full moon, 3rd quarter moon; Period 29.5d (synodic month)
- Angular distance from
Earth-Sun line (elongation) at each phase
- 0o new
- 90o east 1st quarter
- 180o full
- 90o west 3rd quarter
- Lunar calendar 12
to 13 synodic months; not an integral number of lunar month in solar year
- Configurations of the
planets
- Inferior planets:
Mercury and Venus with orbits smaller than Earth's
- Configurations relative
Earth-Sun line
Configuration
Elongation
|
inferior conjunction
|
0o
|
greatest western
elongation
|
48o Venus
|
superior conjunction
|
0o
|
greatest eastern
elongation
|
48o Venus
|
inferior conjunction
|
0o
|
|
- Superior planets:
Mars, Jupiter, Saturn (Uranus, Neptune, and Pluto) with orbits larger than
Earth's
- Configuration relative
Earth-Sun line
Configuration
Elongation
|
opposition
|
180o
|
eastern quadrature
|
90o east
|
conjunction
|
0o
|
western quadrature
|
90o west
|
opposition
|
180o
|
|
- Synodic period: time
for planet to move through successive configurations
- Sidereal period: time
for 360o revolution
Planet
Synodic
Period
|
Sidereal
Period
|
Mercury
|
116d
|
0.24y
|
Venus
|
584d
|
0.62y
|
Mars
|
780d
|
1.9y
|
Jupiter
|
399d
|
12y
|
Saturn
|
378d
|
29y
|
Uranus
|
370d
|
84y
|
Neptune
|
368d
|
165y
|
Pluto
|
367d
|
248y
|
|
- Babylonians continuous
observations of planetary configurations from at least 2000 B.C. onward
- Babylonian mathematical
astronomy reaches peak around 300 B.C.
- Lunar and solar eclipses
- Cause
- Sun 400 times larger
than Moon
- Also 400 times farther
away
- Sun and Moon each
have 0.5o angular size seen from Earth
- Solar eclipse occurs
when shadow of Moon falls on Earth's surface
- Lunar eclipse occurs
when Earth's shadow falls on Moon's surface
- Solar eclipse criterion
- 5o angle between
orbital planes of Moon and Earth
- Moon must be near
new phase and near line of intersection between orbital planes (nodal
line)
- Lunar eclipse criterion
- Moon must be near
full phase and near nodal line
- Types of solar eclipses:
total, annular, partial
- Types of lunar eclipses:
total, partial
- Frequency: typically,
2 solar and 2 lunar eclipses per year
- Saros, 18.6y-period
or 223 lunations between repetition of lunar and solar eclipses
- Assyrian observations
of eclipses from 700 B.C. onward
4.
Egyptian and Babylonian Cosmology
- Organization of world
as fit place for human occupation told in heroic myths
- Myth-making view of
world: "...imagery of myth is...nothing less than a carefully chosen cloak
for abstract though representing the form in which experience has become conscious."
H. Frankfort and H. A. Frankfort
- Astronomical accomplishments
for utilitarian purposes, not necessarily leading to world view
- Mathematical accomplishments
again for practical purposes and not a world view
- Are these not really
more technological - survival - accomplishments than science as we view science?
by J. C.
Evans (1995) All rights reserved to Author. Text reproduced here for
aid in studies and research.
Physics & Astronomy Department, George Mason University
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