2. PREHISTORIC COSMOLOGY

• an era characterised by a general lack of written records
• knowledge largely passed on by word of mouth - symbolic stories and myths
• fossil records of such oral traditions do exist - for example, the Polynesians knew how to navigate between islands of the Pacific by star watching.

Details of the level of understanding attained by ancient cultures:

2.1 Sun (and its diurnal motion)

- position on the horizon where Sun rose and set observed

- Sun's position relative to the stars followed

It was discovered that these both changed smoothly with time and in a cyclic way - that is, the whole thing would repeat itself a certain time later.

The seasons, also, were correlated with the Sun's position on the horizon and with respect to the stars.

Sun used as a time-keeper for agricultural and ceremonial purposes.

[Stonehenge - most famous example of a horizon calendar (??) built by prehistoric civilisation.]

2.2 Moon

- rapid movement of moon with respect to background stars

- change in apparent shape from night to night

- existence of a lunar cycle where changes in shape repeated themselves every $\sim 30$ days

Provided another `time-piece', in particular defining the period of a month.

2.3 Solar & Lunar Eclipses

- Sun on rare occasions noted to be occulted by the moon

- Moon on rare occasions noted to be dimmed (by earth blocking its view of the Sun)

Solar & lunar cycles understood so well that eclipses could be predicted!

2.4 Planets

- distinguished via their brightness (especially Venus, Jupiter, Saturn) and their disobeying the same cyclic motion as the rest of the stars in the sky. [Greeks called them ``planetai'' meaning ``wanderers'']

- these ``wanderers'' noticed to always move within a narrow band on the sky $\rightarrow$ Zodiac [from the Greek word ``zoidion'' - sculptured animal figure, referring to a circle of animals]

- apparent motion of planet with respect to the stars appeared from time-to-time to change direction $\rightarrow$ RETROGRADE MOTION! Retrograde motion a real spanner in the works for a geocentric universe with everything rotating in the one direction about the earth.

2.5 Stars

- provided a fixed backdrop with always the same fixed patterns seen (=constellations). Thought to be fixed points of light on the inner surface of a geocentric sphere $\rightarrow$ the CELESTIAL SPHERE.

- always rose in the east, travlled westward, and set in the west.

2.6 The Babylonians: A case-study of prehistoric astronomy/cosmology (1600BC)

Astronomy:

- extrenely careful observers as a result of state support for keeping the calendar and practising astrology (=influence of stars/planets on human events)

- actually did record their observations (on clay tablets)

- detailed measurements of the angular size of a planet's retrograde loop & the duration of this motion $\rightarrow$ could predict future positions of planets & retrograde motions

- predicted eclipses

BRILLIANT ON PREDICTION BUT NO EXPLANATION OF WHY!!

Cosmology:

- entirely divorced from their vast bank of astronomical knowledge as a result of their religion

- cosmic picture = a world created, ordered and controlled by various gods; the functions of these gods explained by myths. Example: the world was formed from initial chaos by the god Marduk (identified with Jupiter) with the stars being created from an unordered swirl of primeval waters.

ASTRONOMICAL OBSERVATIONS STRICTLY FOR PREDICTIONS!!