Ancient astronomy

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The astronomy developed in ancient Greece is on the one hand the basis of today's celestial science , on the other hand it represents the beginning of natural science in general.

Although it is based on the ideas and data of Mesopotamian astronomy , it goes far beyond them through a real scientific interpretation of the celestial phenomena and the development of special measuring instruments .

There are few direct sources from ancient astronomers, but many works are cited in the writings of Greek natural philosophers, while others were preserved through translations into Arabic .

Ionic natural philosophy

The beginnings of Greek astronomy can be traced back to the research of the Ionian natural philosophers . Its most famous representative was Thales of Miletus (Θαλῆς ὁ Μιλήσιος, approx. 624-547 BC). The mathematician and astronomer is considered to be the first philosopher and scientist of the occidental tradition.

He probably acquired his astronomical knowledge on a study trip to Mesopotamia and / or Egypt . Because one of his outstanding achievements was the precise prediction of the solar eclipse of May 28, 585 BC. BC in Asia Minor, during which the forewarned Lydian army won the long war against the Medes . The Saros cycle , with which eclipses are repeated every 18.03 years, was probably already discovered by ancient Babylonian or at least Chaldean (neo-Babylonian) priest astronomers.

Early Greek astronomy also included Mesopotamian dates for other celestial cycles, such as the synodic month with 29.53062 days (true value 29.53059 days), the exact length of the year and ecliptic inclination and the orbital times of the 5 known planets. For Venus and Mars they were accurate to an impressive 0.2 hours and 1 hour, respectively. The high precision of these numerical values ​​is based on measurement data over 25 centuries, of which thousands of clay tablets have been found. Mediated by Greece, Europe also adopted the Egyptian 24-hour counting, the 360 ​​° of angle measurement and mathematical methods for the advance calculation of lunar and planetary words (see ephemeris ).

Thales' student and successor Anaximander had the revolutionary idea that the earth floats freely in space, whereas it was previously thought of as an island on the primordial sea. This and the spherical shape of the earth postulated by Pythagoras opened up the possibility of developing a first geocentric view of the world . The earth stands in the center of the universe and is orbited by the moon, the sun and the five planets visible to the naked eye on concentric, transparent spheres . The outermost spherical shell with the starry sky rotates evenly in 23 hours 56 minutes. In the popular imagination this is done by a deity (see myth of the sun chariot ), while later for the polymath Aristotle (384–322 BC) it is the action of the world creator ( immobile mover ).

Geocentric world system

In the homocentric system of Eudoxus from Knidos (approx. 395-340 BC) all movements take place on circular orbits around the center of the earth. But while the sun is still circling the earth relatively evenly (albeit at an angle of 23.5 ° to the celestial equator ), three noticeable inequalities must flow into the calculation model for the lunar orbit (later even 12 additional parameters were introduced for this). It gets even more difficult with the planets, because every year they describe a loop of several months under the stars . In the case of the outer planets, it can be explained by the faster earth orbit around the sun, as Copernicus recognized in 1543. For these additional movements, Apollonios von Perge (262–190 BC) and Hipparchus von Nikaia (190–120 BC) used eccentric circular orbits with attached epicycles .

The highest precision of geocentrics , however, was only achieved 300 years later by Claudius Ptolemy (approx. 100–160 AD). He introduced further inclinations of the orbit of the auxiliary circles as well as compensation points around fictitious, eccentric points and determined the lunar orbit as an express line at an average of 60 earth radii away. This standard model could explain all freely measurable celestial movements and was unchallenged until the 16th century - which makes Ptolemy the most important astronomer of all time. The heliocentric world system published by Copernicus in 1543 could not be definitively proven until 1838 by Friedrich Wilhelm Bessel . Because that behind the orbit of Saturn there should be an enormous emptiness of more than 4 light years , many scientists of the modern age also seemed implausible.

An early predecessor of Copernicus was Aristarchus of Samos (310–230 BC), who made the earth orbit the sun. He was accused of godlessness and atoned for his tenacity with several years of exile. An intermediate model goes back to Herakleides Pontikos (approx. 390-320 BC), in which the inner planets Mercury and Venus orbit the sun, which in turn rotate around the central earth like the moon and the sphere of fixed stars. A similar compromise between geocentric and heliocentric systems was also represented by Tycho Brahe around 1590 .

More theories and findings

In the school of the Pythagoreans , instead of the rotating starry sky, there was speculation about a possible earth rotation . This theory of the Hiketas of Syracuse arose out of philosophical and mechanistic considerations, but did not gain general acceptance.

Philolaos imagined the movement of the earth together with a counter- earth , the sun and all planets around a mythical central fire . The counter-earth is invisible because it conceals the earth's body from our view. This pyrocentric system was founded by Philolaos et al. a. with the sacred ten for the number of heavenly bodies involved.

Plato formulated a divine world creation based on the ideal of a circle and sphere . It had an impact far beyond antiquity - and gave Johannes Kepler long-standing doubts as to whether the planetary orbits could really be ellipses . Plato and the Neoplatonists also philosophized about light and a possible mysticism of light .

His student Aristotle developed the fundamentals of ancient physics , which prevailed until the beginning of the modern era . The universe possesses two physically different areas - the sublunar of the four elements and the supralunar of the ether . The heavy materials naturally sink to the center of the world (i.e. tend towards the geocenter ), the light materials rise. Every force causes movement (instead of acceleration ). This physical system was only revolutionized by Galileo .

Physical aspects

It would be an exaggeration to attribute the beginning of an astrophysics to ancient Greece . Nevertheless, essential considerations were raised:

literature

Individual evidence

  1. ^ John M. Steele: A Brief Introduction to Astronomy in the Middle East. Saqi, London 2008, ISBN 978-0-86356-428-4 .
  2. ↑ Jürgen Mittelstrass, Art. Geocentric, geocentric world system , in: HWPh vol. 3, p. 329 ff.
  3. ↑ O.Becker 1957: The mathematical thinking of antiquity , p.80 ff
  4. ↑ Because of these movements, which were puzzling until the Middle Ages, the Babylonians assigned a deity to each planet, to which today's Latin planet names correspond