3.1. 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
3.2. 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
3.3. 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
3.4. 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?
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