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

• Superior planets: Mars, Jupiter, Saturn (Uranus, Neptune, and Pluto) with orbits larger than Earth's

 

• Configuration relative Earth-Sun line

• Synodic period: time for planet to move through successive configurations

 

• Sidereal period: time for 360o revolution

• 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

Back to the Introduction Overview

Home