Geocentric model

In a geocentric universe (Greek γεοκεντρικό geokentrikó " erdzentriert " ) the Earth was at the center of the universe. Moon, Sun and planets orbit the Earth on geometric curve movements. The homocentric system as one of the varieties of geocentrism this is done in several, arranged concentrically from the inside to the outside spheres. The axes of the orbits go through the center of the earth here. These spheres were partially conceived as a transparent hollow spheres. The outermost sphere is occupied by the fixed stars. After the epicycle the earth is indeed still in the center, the planets describe them, but not a perfect circular orbit more. The geocentric view is not identical with the concept of a flat earth. Since Aristotle, a spherical shape of the Earth has been predominantly represented in the context of a geocentric. It is the result of systematic observations and precise calculations. Until his replacement in the Renaissance it was about 1800 years the prevailing opinion.

• 2.1 The case of Galileo Galilei

Ancient Greece

The earth in the center

The geocentric view was introduced in classical antiquity in Greece and sat down opposite opinions early example Aristarchus of Samos by, the thought, not the earth, but the sun was at the center of the cosmos. By the end of the Middle Ages the geocentric world view in Europe was widespread. In ancient China and in the Islamic world it was taught. Whether it was represented before the Greeks in Mesopotamia, is not certain. The geocentric world view is based on the assumption that the earth and thus indirectly also the man should be in the center of the universe, and that all the movements of the moon, the sun and the planets expired geometrically curve movements around the as dormant or around its axis rotating imaginary world. When homocentric system of Eudoxus of Cnidus this curve motion takes place on circular orbits, whose axes go through the center of the earth and thus appear perfect. Already Apollonius of Perga and Hipparchus took for their models of planetary movements eccentrics and epicycles to help. Ptolemy worked with compensation points are fictional, eccentric location points with the inclusion of eccentrics and epicycles to receive. Heraclides Ponticus is partially attributed to a system in which the planets Mercury and Venus revolve around the sun, in turn, like the moon and the sphere of fixed stars revolves around the preserved in its central position earth. This would represent a compromise between the geocentric and heliocentric world system. In more recent research, the world system of Heraclides, however, highly controversial. The most important justification for the assumption of the geocentric world view was the observation of gravity, which could be explained by the fact that all seriousness its natural location, the center of the world zustrebe. Aristotle, too, was an influential advocate of the geocentric worldview. The Aristotelian physics is compatible but not strictly with the auxiliary assumptions of eccentrics, epicycles and balance points. It's best to harmonize with the homocentric variant. From the sun and the planets they took part in, they were of an unearthly " fifth element ", the quintessence, whose natural motion is the circular path.

Ptolemaic world view

The work of Claudius Ptolemy math Matices syntaxeos biblia XIII has laid down the geocentric view of the world for nearly 1500 years. He used the so-called epicycle, as far as is then spoken by the Ptolemaic worldview. A challenge for the geocentric worldview was the seemingly sudden rearward movement of the outer planets, such as Jupiter, against the star background. She makes at the Erdperspektive to an apparent loop motion of the planet. This also known as " retrograde motion " described phenomenon occurs just when the planet is closest to the Earth. To bring the astronomical observations with the geocentric world view in line, it was necessary to leave a portion of the celestial bodies -widening circles around this track on their tracks. These are the so-called epicycles. Thereafter, the outer planets move in a circular path about an imaginary point which, in turn, orbits the earth. A planet moves initially at a uniform traversed wearing circle ( deferent ). In this rotates uniformly a second circle, the so-called Aufkreis ( epicycles ). The planet itself runs uniformly around on the Aufkreis. The center of the Aufkreises rotates uniformly around the center of the support circle. This raises the observed from Earth orbit planet as a superposition of these movements dar. part way then even more tracks were modeled around these circles. Calculations within this model were very complicated. Through the use of about 80 such webs Ptolemy was able to bring the then possible observations of planetary motion in accordance with the geocentrism. When the sun does not occur retrogression. The Ptolemaic astronomy associated with the planetary motion of the sun circulation under the premise of geocentrism and enabled with its complex model largely accurate predictions. In the heliocentric world view epicycles, however, are unnecessary.

The Christian churches

The geocentric view was close to the everyday experience of the observer and did not contradict the Bible. The Christian churches took over and defended it decided. It first went on the Greek Church Fathers such as Basil the Great ( 330-379 ). He treated in nine homilies exegetical the creation account and drew a picture of nature, which built directly on the antique. His Lenten sermons influenced his friend Ambrose of Milan ( 340-397 ). About this it was also known Augustine of Hippo, who was a pupil of Ambrose. The original texts of Ptolemy were not available in the West in the Middle Ages, and his theories of Aristotle were known mainly by Latin Kompendienliteratur. Few monk scholars dominated at all Greek. The scholastics of the 13th century saw in the absolute center of the earth, with the man's position is defined. Contrast, was in the highest sphere of heaven, the kingdom of God and the saints: the empyrean.

The geocentric view was not questioned in the Middle Ages and in the early Renaissance. Sustainable doubt came up only with Nicolaus Copernicus ( 1543). Galileo Galilei was eventually indicted for his advocacy of the heliocentric system of Copernicus by the Inquisition for heresy.

The case of Galileo Galilei

When Galileo beginning of January 1610 with the first telescope discovered the four largest moons of Jupiter, it seemed shocking. It disagreed with the idea that the earth was the center of all the celestial motions. On the advice of Cardinal Robert Bellarmine, a theological opinion was drawn up on behalf of the Pope, who came to the following conclusions:

" 1 The sun is the center of the world and is completely immobile in space. Criticism: The general opinion this sentence is philosophically foolish and absurd, and formally it is heretical, inasmuch as it contradicts the express opinion of the Scriptures, as appearing in many places, and although its wording itself as well as the accepted interpretations of these posts and the opinions of the fathers of the Church and theology. 2 The earth is not the center of the universe nor immovable, but moves as a whole and is located in a daily movement. Criticism: All say for this set is true philosophically the same as for the previous one, and in terms of theological truth it is at least moderately erroneous belief ".

The Inquisition forced Galileo to recant his theses, with which he had affirmed the finding of Copernicus that the earth revolved around the sun. In the 17th century, followed by the Catholic side, numerous attempts to defend geocentrism. A well-known main representative was there the Jesuit Giovanni Battista Riccioli, who was professor of philosophy, theology and astronomy in Ferrara. Galileo's books were until 1835 on the Index of Forbidden Books ( Index Librorum Prohibitorum ). He was officially rehabilitated until 1992.

Tycho Brahe

Tycho Brahe identified the imaginary point of Ptolemy with the sun, but still remained basically the geocentric worldview. In his system, moon and sun revolve around the earth, the other planets revolve around the sun moving. It is a compromise between the geocentric and heliocentric world system.

Heliocentric world picture

Only through the preparatory work of Nicolaus Copernicus and especially after Johannes Kepler had come by the object of the theory of circular motion to very simple mathematical laws of elliptical planetary motion, the geocentric world view turned out to be outdated. It was ultimately replaced by the simpler and mathematically more easily usable heliocentric world view that with Isaac Newton's theory of gravitation was also excellent theoretically explain a little later. The distinction between terrestrial and celestial matter could thus be omitted.

The Milky Way

Already Galileo Galilei had seen that the fog of the Milky Way - in which our solar system is located - is composed of stars. Born in Hanover in 1738 William Herschel made ​​on the basis of observations by Charles Messier a catalog of 2500 nebulae together. These structures then turned out to be for the most part as galaxies similar to our Milky Way. After the discovery of the structure and rotation of the Milky Way, the sun could no longer be considered as the center of the universe. The center of mass of the Milky Way is called the galactic center. It lies in the constellation Sagittarius. There, the visible band of the Milky Way appears thickest. The galactic center contains the nearest known to us supermassive black hole. The modern cosmology and according to Einstein's theory of relativity can be combined with scientific methods an absolute center of the universe did not identify. Despite these scientific debates vote in polls in Western societies regularly 20-30 % of the respondents agree with the statement that the sun revolves around the earth. In everyday subjective perception of the observer on the earth the sun, moon and planets move further to its relative point of observation: "In the morning the sun rises ".