Ancient Greeks:
Sensitive and long time span astronomical observations made by Babylonians formed the basis of ancient Greek astronomy. The ancient Greeks focused on their causes rather than astronomical events and formed the first models of the universe. In these models, it was accepted that the stars were perfect bodies for the gods and that they made perfect movements.
What the ancient Greeks called this perfect motion is the assumption of uniform circular motion. Until Kepler's time, it remained an indispensable assumption of astronomical thought.
According to Tales, the first natural philosopher we know of the ancient Greeks (640-546 BC) (Picture 8) The earth was a flat disk floating in water. Tales never commented on the movements of planets and stars. Tales' contemporary Anaksimander (611- 547 BC) suggested that the Earth is a floating cylinder in space. B.C. In the 6th century, two independent schools were formed. According to the school of Xenophanes (Senofanes) (570-500 BC), the earth was flat and of infinite dimension, the second Pythagorean (Pythagoras) school (580-500 BC) was mostly based on observations.
Pythagoras, after long journeys on the Earth, believed it to be spherical. Although they believed the earth was round, no one from this school advocated that he had returned. According to this school, the number 10 was perfect as it was 1 + 2 + 3 + 4 = 10. At that time, 9 different celestial bodies (Earth, Moon, Sun, five planets and fixed stars) were observed.
This number should have been 10 because of perfection and symmetry. As the 10th object, they claimed that Earth had a match. Again, according to this school, 10 different celestial bodies were making an orbital movement around an invisible fire center because they were covered by the Earth's partner. According to this view, Earth was considered for the first time as an orbital planet.
B.C. Anaxagoras (Anaxagoras), who thought that the ferrous meteorite that fell in Greece in 467 came from the Sun (M.O. 500-428) thought that the Sun was close and small as a part of Greece, and its substance was molten iron; According to Anaxagoros, the place was flat; The Moon was about the size of the Sun and the Moon reflected the sunlight. Anaxagoras was wanted to be punished with these views and was saved from death by Pericles and sent into exile.
An important school of the later period is named after Plato (Plato) (427- 347 BC). Plato himself was influenced by the Pythagorean school and developed the views of that school. He believed in the existence of a geometric order in the universe and the relative distances he believed for seven celestial bodies (Moon- 1, Sun- 2, Venus- 3, Mercury- 4, Mars- 8, Jupiter- 9, Saturn- 27); He has shown it with two geometric series, 1, 2, 4, 8 and 1, 3, 9, 27.
Plato also believed in and developed the concept of invisible musical crystal spheres carrying celestial bodies that the Pythagorean school believed. Plato believed that the daily visible movements of the celestial bodies were caused by the rotation of the Earth.
The common view of the Plato (Plato) school predicted that the Earth was different from all other celestial bodies and that it should be at the center of the universe. We see that Eudoxus (Eudoksus) (408- 355 BC) proposed the geocentric universe model for the first time in ancient Greece. According to Eudoxus, the Moon, Sun and 5 known planets orbit around the fixed Earth in concentric circles, and it is Eudoxus who introduced the concept of the secondary sphere (epicycle) into the planets theory.
When Eudoxus saw that the model he developed did not fully provide the observations, he thought that there could be other smaller and invisible spheres on the invisible spheres that Philolaos (Filolaus) assumed. According to him, the planets were located on these secondary spheres. The total number of spheres invisible in Eudoxus' model of the universe is 27.
In this geocentric model, which was later supported and developed by Galluppus, Aristotle, Hipparchus (Hipparchus) and Ptolemy (known as Ptolemy in the Arab world), the complex visible motions of the planets could easily be explained, but as the sensitivity of the observations increased, it was necessary to increase the number of secondary spheres to explain the deviations from the model.
Aristotle showed that the Earth is a very large sphere with two important proofs. During a lunar eclipse, the shadow boundary of the Earth on the Moon is a wide arc and new stars are visible as one goes south over the Earth. Aristotle suggested that polar radiation, flowing stars and comets are events in the upper atmosphere of the Earth.
Heraclitus, who lived in Aristotle's period (388-315 BC) claimed that the spherical Earth rotates around an axis and that the universe is infinite Mercury and Venus revolve around the Sun. It continued until the renaissance period. The 5 known planets (Mercury, Venus, Mars, Jupiter and Saturn), Moon and Sun made up the magic number 7 in Aristotelian times.
The earth was not considered a planet at that time and was given a great privilege in all respects. Around the earth, 7 invisible crystal balls of 7 celestial bodies divide the universe into 7 layers. Hence the concept of "7 layers of heaven" which is frequently mentioned in the holy books of monotheistic religions. 7 days a week is also from the same source. Even the source of the musical notes is related to the 7-storey universe model.
According to the belief at that time, 7 large invisible spheres carrying 7 celestial bodies should have been made of crystal and the sound they made while they were spinning could be heard by those who were free from their sins. In ancient Greece, with the imitation of the sounds that such people hear, seven basic musical notes as the sounds of seven crystal spheres and flats and sharps with the sounds of secondary spheres emerged.
About a century after Aristotle, Aristarchus of Samos (312-230 BC) proposed a heliocentric model for the first time. Aristarchus may have advocated the heliocentric model by placing the Sun at the center of the universe because of its size.
At the time of Hipparchus (190-125 BC) (Figure 9), planetary luminosity was known to vary throughout the year. Hipparchus, thinking that the planet-Earth distance should vary throughout the year, argued that the Earth should not be at the center of the invisible spheres in the Earth-centered model.
By comparing the star positions in his star catalog with the previously recorded positions of the same stars, Hipparchus noticed a continuous but very slow change in positions. Hipparchus' main contribution to astronomy was that he developed the measuring system of stellar luminosity used today.
Later, Ptolemy (M.S.100-170) (Figure 10) adopted the Earth-centered universe model, taking Hipparchus as an example in the subject of the universe model. He determined the conjunction periods of the planets and calculated their distances to the Earth in geometrical ways. Ptolemy's most important contribution to astronomy is his 13-volume astronomy book.
Ptolemy collected all the astronomy knowledge of his time in this book, which is called Almagest in the Arab world. Including Hipparchus' star catalog, this book has been used as a basic astronomy book for centuries. Hipparchus' star catalog is important in terms of giving the brightness and coordinates of the stars visible at that time. By comparing the current coordinates of the same stars with the values in the Hipparchus catalog, the core motions of those stars and, if any, very long-term changes in luminosity can be found.
With the rapid spread of Christianity within a few centuries after Christ and the collapse of the Roman Empire, the importance given to science in Europe almost disappeared, and Europe entered a dark period with the establishment of Aristotle's thought in the church.
