Astronomical picture of the world
For centuries, man has sought to unravel the mystery of the great world “order” of the Universe, which the ancient Greek philosophers called Cosmos (translated from Greek – “order”, “beauty”), in contrast to Chaos, which, they believed, preceded the appearance of Cosmos.
The first natural science ideas that came to us about the Universe surrounding us were formulated by ancient Greek philosophers in the 7-5 centuries. BC e. Their natural-philosophical teachings relied on previously accumulated astronomical knowledge of the Egyptians, Sumerians, Babylonians, Aryans, but were distinguished by a significant role of explanatory hypotheses, a desire to penetrate the hidden mechanism of phenomena.
Observation of the circular disks of the Sun, the Moon, a rounded horizon, as well as the border of the Earth’s shadow crawling on the moon during its eclipses, the correct repeatability of day and night, seasons, sunrises and sunsets – all this suggested that the structure of the universe is at the core the principle of circular forms and movements, “cyclicality” and uniformity of changes lies. But up to the 2nd century. BC e. there was no separate doctrine of heaven, which would combine all the knowledge in this area into a single system. Representations of celestial phenomena, as well as phenomena “in the upper air” – literally about “meteor phenomena”, have long been included in general speculative teachings about nature in general. These teachings were later called physics (from the Greek word “fusis” – nature – in the sense of periods, the essence of things and phenomena). The main content of this ancient semi-philosophical “physics”, or, in our understanding, rather of natural philosophy, which included almost the main elements of cosmology and cosmogony, was the search for that invariable beginning, which was thought to underlie the world of mutable phenomena.
All the knowledge of nature accumulated over centuries, right up to the technical and everyday experience, was combined, systematized, logically extremely developed in the first universal picture of the world, which he created in the 4th century BC. e. the greatest ancient Greek philosopher (and, in fact, the first physicist) Aristotle (384 – 322 BC) spent most of his life in Athens, where he founded his famous scientific school. This was the doctrine of the structure, properties and movement of everything that is included in the concept of nature. At the same time, Aristotle for the first time separated the world of earthly (or rather, “moonlit”) phenomena from the heavenly world, from the Cosmos proper with its supposedly special laws and the nature of objects. In a special tract “about the sky” Aristotle painted his natural philosophical picture of the world.
By the Universe, Aristotle meant all existing matter (consisting, according to his theory, of four ordinary elements – earth, water, air, fire and the fifth – celestial – ever moving ether, which also differed from ordinary matter in that it had no lightness, no severity). Aristotle criticized Anaxagoras for identifying the ether with the ordinary material element – fire. Thus, the universe, according to Aristotle, existed in the singular.
In the world picture of Aristotle, the idea of the interconnectedness of the properties of matter, space and time was first expressed. The Universe seemed finite and limited to a sphere beyond which nothing material was thought, and therefore there could not be space itself, since it was defined as something that was (or could be filled with matter). Outside the material universe there was no time, which Aristotle with brilliant simplicity and clarity defined as a measure of motion and connected with matter, explaining that “there is no movement without a physical body.” Outside the material universe, Aristotle placed the intangible, spiritual world of the deity whose existence was postulated.
The great ancient Greek astronomer Hipparchus (c. 190-125 BC) was the first to try to reveal the mechanism of the observed movements of the bodies. To this end, he first used in astronomy the geometric method for describing non-uniform periodic motions as a result of adding simpler – uniform circular ones, proposed a hundred years before by the famous mathematician Apollonius of Perga. Meanwhile, it was Plato who called for the disclosure of the simple essence of the observed complex astronomical phenomena. Uneven periodic motion can be described using a circular motion in two ways: either by introducing the concept of an eccentric – a circle along which it is displaced relative to the observer, or by decomposing the observed motion into two uniform circular ones, with the observer in the center of the circular motion. In this model, it is not the body itself that moves around the observer in a circle, but the center of the secondary circle (epicycle), along which the body moves. The first circle is called the deferent (carrier). Subsequently, both models were used in ancient Greek astronomy. Hipparchus used the former to describe the movement of the sun and moon. For the Sun and the Moon, he determined the position of the centers of their eccentrics, and for the first time in the history of astronomy he developed a method and compiled tables for predicting the moments of eclipses (accurate to 1-2 hours).