Up: Astronomy 9 Lecture Notes

ASTRONOMY 9: HISTORY OF COSMOLOGY

Handout #7

J. E. Baker
UC Berkeley, Spring 2000

Astrology and Ancient Astronomy

1.

Astrology vs. Astronomy

Do not confuse these, or you will offend your friendly neighborhood (modern) astronomer!!
Astronomy: science of the heavens
Cosmology: study of the universe as a whole (incorporates a wide range of physics and astronomy)
Astrology: unfounded superstition

2.

Why discuss astrology in a history of science course?

Until about 1700, little distinction between astrology/astronomy (e.g., Kepler)!
Nearly half of Americans today still believe astrology has some ``scientific'' validity!
Important to understand why, and how to challenge
Astrology is as implausible as ``jetology'' (see Fraknoi article in reader)

3.

History of astrology (Cowling)

Chaldean (Mesopotamian) astrology
- Little concern with individual personal forecasting
- Forecasts for empires, wars, etc.
Ptolemy (2nd century AD, Egypt, Greek Empire)
- Systematizes Sun-sign astrology in Tetrabiblos
- Similar to modern form of astrology
Greek skeptics (e.g., Carneades)
- Why can twins with same horoscope suffer different fates?
- Not all men who fall in the same battle have the same horoscope.
- Personal characteristics more tied to, e.g., ethnicity than time of birth
Christianity
- St. Augustine (5th century AD)
  - Astrology leaves no room for God's will
  - Must be associated with devil
- Degree of repression of astrology varies
Question of free will vs. determinism
- The stars ``tilt but do not compel''?
Some modern arguments against astrology (see also articles in reader)
- Why is time of birth more important than conception?
- Why isn't the astrologer rich(er)?
- The signs (constellations) are illusory: stars at different distances, patterns change completely over millions of years
- Precession of the equinoxes (26,000 yr period)
  - Signs have moved out by one whole place!
  - Astrologers still use old dating system
  - Sun is now in Ophiuchus for several days each year; why isn't it a sign?
- New planets: Uranus, Neptune, Pluto
- Bizarre nature of the implied ``force''
  - If depends on distance (like gravity or EM), cell phones and books should have far greater influence
  - If independent of distance, what about quasars, neutron stars, etc?
- Astrology falsely assigns central importance to humanity, Earth's place in the cosmos
  - Product of an Earth-centered cosmic system
  - Celestial physics thought very different from earthly
  - ``Wanderers'' (visible planets, sun, moon) thought to have divine power, influence over man
- Today we know planets are just big balls of rock and gas!
- No more influence on your personality than the positions of all the world's jets (``jetology'')

4.

Basic motions in the sky visible to naked eye

Daily (diurnal) rotation of ``sphere'' of the heavens
- Really rotation of Earth about its axis
- Axis is inclined by $23.5^\circ$ to orbital plane
Sun, Moon, planets (``wanderers'') confined to a strip around the sky (ecliptic, constellations of the zodiac)
Approximately annual motions of Wanderers along the ecliptic
- Really orbital motion of Earth around Sun, plus planetary orbital motions
Complicated behavior: planets sometimes stop and reverse course for a while (retrograde motion)
At noon, Sun is furthest north on summer solstice, furthest south on winter solstice, crosses celestial equator at spring/fall equinoxes
Monthly motion of Moon, 29.5-day cycle of phases
- Eclipses are rare (not every month) because Moon's orbit is tilted by $5^\circ$ compared to plane of Earth's orbit
Precession of the equinoxes
- 26,000-year circular motion of Earth's axis
- North Pole currently points near Polaris, but not always!
- Motion like a spinning top
Stars seem fixed on timescale of civilization, but really move

5.

Ancient Astronomy

Very old! Lascaux cave paintings, about 17,000 BC!
Celestial events are predictable (if you wait long enough to see the pattern, and/or understand why they occur)
Alone among ``exact'' sciences for thousands of years
Astronomical order tied to social and religious needs
- Time-keeping and calendars
- Agriculture: when to plant or harvest crops
- Religion: gods control heavenly events
Egypt
- Pyramids are monumental feats of engineering
- Celestial alignments accurate to a few arc minutes (1/60th of degree)!
- Used diurnal motions as a clock
Babylonia
- Developed sexagesimal (60) counting system
  - Still used for time (hours, min, sec) and angles (degrees, arc-minutes, arc-seconds)!
- Tables of planetary motion
- Prediction of eclipses and heliacal risings (first appearance after invisible due to being near the sun)
- Predictions made by looking for patterns in the times of events
- No understanding of why events occurred, no pictures of orbits, no geometry!
China
- Well-preserved historical records dating back 3000 years
- Oldest records of comets, eclipses, sunspots, etc.
- Recorded supernovae in 1006 and 1054 (mostly ignored in Europe though as bright as full moon!)
- Astronomy tied to political bureaucracy and functioning of government
- Decline in importance of astronomy after about 1200 AD
Mayans (S. America)
- Complicated, highly accurate calendar system
- Precise tables for motions of Moon and Venus
- Prediction of solar eclipses
Celts
- Stonehenge: impressive stone monument, approx. 2000 BC
- Purpose and function unknown; probably religious, probably not an astronomical calculator
- At least one astronomical alignment: sunrise at summer solstice

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Up: Astronomy 9 Lecture Notes

jonathan baker
2000-03-05