Since the first Egyptian farmers discovered the annual reappearence of Sirius just before dawn a few days before the yearly rising of the Nile, ancient civilizations around the Mediterranean have sought to explain the movements of the heavens as a sort of calendar to help guide them conduct earthly activities.
Counting phases of the moon or observing the annual variations of daylength could, after many years' collection of observations, serve as vital indicators for planting and harvesting times, safe or stormy season for sailing, or time to bring the flocks from winter to summer pastures .
With our millenia of such observation behind us, we sometimes forget that seeing and recording anything less obvious than the rough position of sun or nightly change of moonphase requires inventing both accurate observation tools (a stone circle, a gnomon used to indicate the sun's shadow, a means to measure the position of stars in the sky) and a system of recording that could be understood by others (how many fingers' width or degrees is that star from the horizon? Which direction is due north?).
The ancient Greeks struggled with these problems too, using both native technology and inquiry, and drawing upon the large body of observations and theories gradually gleaned from their older neighbors across the sea, Egypt and Babylonia.
Gradually moving from a system of gods and divine powers ordering the world to a system of elements, mathematics, and physical laws, the Greeks slowly adapted old ideas to fit into a less supernatural, hyper-rational universe.
This paper is a short survey of the Greeks' earliest attempts to explain why and how the sky changes.
As ancient peoples began to realize that sun, moon and stars follow certain rhythms in step with the seasons, they made the leap of thought to postulate that some conscious set of rules must be dictating these movements and seasonal changes which, for agrarian or pastoral societies, were a matter of life or starvation. Who or what could be causing these all-important changes to come about? Certainly nothing on earth, no beast or human, had the power. Thus gods were born.
There are hints of the Greek conception of the universe in Homer, who mentions many subjects on his two epics describing war and the perils of trying to come home after long absence. For Homer, heaven is a solid inverted bowl (Od. 15.329 sideron ouranon) straddling the earth, with fiery, gleaming aither above the cloud-bearing air. (Il. 14.288 `fir-tree reached through the aer to aither).
Homer mentions the movements of sun, moon, and many stars by name.
The fact that Hades is on the underside of earth has an important impact on conceptions of heaven: it is unlit by the sun (in Homer and in Hesiod), therefore, the sun--and by extension, other heavenly bodies - must sink only to the level of Ocean, which is conceived as a river circling earth's edge. From it the Sun must also rise -though how it gets back to the eastern bank of Ocean is never explained.
These popular conceptions of sky are more fully explained in Hesiod, whose works on gods and on agriculture and animal-herding are more closely connected to the practical application of astronomy. He clocks spring, summer, and harvest by solstices and the rising and setting of certain stars, and notices that the sun migrates southwards in winter. Night is a substance welling up from under the earth, as if it were a dark flowing mist
Other mythological schemes of the heaven:
One early and popular cult, that of Orpheus, developed its own of gods and universe-creation variant from those in Homer and Hesiod; there, a primeval egg is birthed by the early gods, and the upper half of its broken shell becomes heaven's vault.
Various cults, cities and tribes of Greeks (who were unified only by language and common culture, and both of these had regional variants) probably had different versions of cosmogony and slightly different gods in charge of astronomical movement, but the general physical conception of the sky is alluded to by many authors of plays and other popular works (Eur. Melanippe 484), and was probably held by the majority of people.
The Ionian Revolution: Fiery Clouds and Wheels of the Sky:
Many Greeks settled on the coast of Turkey in the early migrations of the eleventh century BCE, and there enjoyed rich cultural mingling with their neighbors (and sometimes their conquerers) the Lydians and Persians, latest descendents of Mesopotamian civilization.
The freshwater conception of the Ocean river is seen by many scholars as a telltale sign of early adoptations from that ancient `between the rivers' people.
They kept in touch with their western cousins, who began a second wave of settling across the Aegean in the seventh century, as well as with other rich sea-faring cultures like Egypt. It is not surprising that, by the sixth century, these Ionian navigators of the sea began to develop new ideas about the sky they steered by.
The most fundamental of these was that the universe might run, not only by the whim of gods, but by physical, mechanical rules and principles that might, through study, be understood and predicted.
Thales of Miletus (c. 585 BCE): Eclipses and Stellar Studies:
Our sources for all early Greek astronomy are scant, none more so than for Thales, supposedly the first of the philosophers. Various inventions and discoveries are attributed to him, most famous of which is his prediction of an eclipse of 585.
Modern scholars are fairly sure he was able to do this by consulting known Babylonian eclipse and lunar observations going back about 150 years, long enough to notice that eclipses recur after about 18 years.
His activities also seem to have included star-observations and trigonometry, which he is credited with having founded, but the details of his theories are either lost or obscured by later legends about this early thinker who left no written record. He seems to have conceived of earth as flat and water-borne, and to have postulated that there must have been some first substance out of which the world arose, which he guesses is water (Aristot. Met. 983b 6).
Anaximander of Miletus c. 550 BCE: Celestial Fire and Pipes:
The earth for Anaximander is still a cylinder circled by air and then fire "like the bark of a tree" which separated off at an early stage. We still see echoes of the early cosmologies here, but an attempt is made to explain the scheme in purely physical--in fact, in mathematical--terms. The heavenly bodies are all described as wheels of fire (Homerically described as like chariot wheels) enclosed by are via a further separating-off.
Their light which we actually see is only a part of them, described as an axle, pipe, vent, or bellows-nozzle, through which fire jets. Eclipses and lunar variations are accordingly caused by these vents opening or partially closing.
All these ideas are attempt to explain the universe in physical terms, though as yet there is only the vaguest theory as to why these things are so. Anaximander seems to suggest a process of separation and "equilibrium", with the earth suspended in the middle and the various heavenly bodies "balanced" all around it by some unseen rule.
Here, as with all the early thinkers for whom direct quotes are almost non-existent, we must be cautious about later sources who tend to read later theories into ealier philosophers' ideas. Yet with that caution in mind, we can see by Anaximander's "equilibrium" (and the "condensation" of Anaximines and all his successors, next section) that the Greeks were beginning to be aware of gravity but still needed to put two and two together and recognize it explicitly.
Anaximines of Miletus (c. 525 BCE): Condensation of All From Air:
The third of the Ionian thinkers refined the flat-earth idea, suggesting that all things are produced through a process of gradual condensation and "rarification": earth condenses out of air, and fire is "exhaled" from the earth.
The earth and heavenly bodies are flat and loft on infinite air like a leaf. Celestial bodies do not set beneath the earth, just as in mythology, but instead turn at an angle (the axis of rotation, after all, is visible to us in the northern part of the sky) so that many are obscured by the "higher" parts of earth to the north.