| • Science | • People | • Locations | • Timeline |
To anyone who stands and looks at the sky, it is apparent that the earth stays in one place while everything in the sky goes around once every day. Observing over a longer time, one sees more complicated movements. The Sun makes a slower circle over the course of a year; the planets have similar motions, but they sometimes turn around and move in the reverse direction for a while ( retrograde motionThis article is about retrograde motion. For the musical term retrograde see Counterpoint, Musical set theory, Operation, Permutation, and Transformation. Retrograde motion is the orbital motion of a body in a direction opposite that which is normal to sp). As these motions became better understood, they required more and more elaborate descriptions, the most famous of which was the Ptolemaic systemThe Ptolemaic system was a model to explain the motions of the heavens, espoused by Claudius Ptolemaeus in his work, the Almagest some time around the 2nd century, C. and accepted for over 1,000 years by the vast majority of Europeans to be the correct co, formulated in the 2nd century1st century 2nd century 3rd century other centuries) Events Roman Empire governed by the Five Good Emperors' ( 96 180) Nerva, Trajan, Hadrian, Antoninus Pius, Marcus Aurelius. Significant persons Cai Lun, Chinese inventor Galen, medical writer Saint Irena.
The strange idea that it is the other way around—a heliocentric theory— was suggested at least as early as the 4th century BC- In chapter 13 of book two of his On the Heavens, AristotleAristotle ( Greek Αριστοτλης Aristotelēs) ( 384 BCE March 7, 322 BCE) was a Greek scientist and philosopher. Along with Plato, he is often considered to be one of the two most influential philo wrote that "At the centre, they [the PythagoreansThe Pythagoreans were an Hellenic organization of astronomers, musicians, mathematicians, and philosophers; who believed that all things are, essentially, numeric. The group strove to keep the discovery of irrational numbers a secret; and legends tell of say, is fireFire is one of the four classical elements in ancient Greek philosophy and science. Fire is considered to be both hot and dry, and according to Plato is associated with the tetrahedron. Fire is often an image of passion and creativity, its consuming tende, and the earth is one of the stars, creating night and day by its circular motion about the centre." The reasons for this placement were philosophicClassical (or "early") Greek philosophy focused on the role of reason and inquiry. In many ways it paved the way both to modern science and to modern philosophy. Clear unbroken lines of influence lead from early Greek philosophers, through early Muslim ph based on the classical elementSeveral ancient classical element ideas exist. The Greek version of these ideas persisted throughout the Middle Ages and into the Renaissance, deeply influencing European thought and culture. Classical elements in Greece The Greek classical elements are fs rather than scientific- fire was more precious than earth in the opinion of the Pythagoreans, and for this reason the sun (representing fire) should be central. Aristotle dismissed this argument and advocated geocentrism.
Later, heliocentrism was again proposed by Aristarchus (c. 270 BC). By the time he was writing, the size of the Earth had been calculated accurately, and he himself measured the size and distance of the Moon and Sun; his figures were not accurate by modern standards, but a serious start. Perhaps, as many people have suggested, paying attention to these numbers led him to think that it made more sense for the Earth to be moving than for the huge Sun to be moving around it. Some people in his own time, though, considered the idea to be against religion.
Aristarchus' heliocentric model was countered by Archimedes, who argued in The Sand Reckoner that the world (universe) was of large but finite size, and based on his set of initial assumptions he calculated an upper limit to the diameter of the universe to be 10,000,000,000 stadia. Given this number for the size of the universe, it followed that there was maximum distance that stars could be from the center. In a heliocentric system, the earth would move twice the earth-sun distance each year, and given this distance to stars should see visible parallax as it got closer or farther to various stars. As no parallax was observed, heliocentrism was dismissed because it would require the stars to be an implausible (to Archimedes) distance away.
In the 5th century AD (apparently independently of Aristarchus) the Indian astronomer Aryabhata also proposed a heliocentric Universe. As his work was not translated into Latin until after Copernicus had written De revolutionibus orbium coelestium, his theories were generally ignored in the West.
For many centuries, Heliocentrism was countered with the apparent common sense view that, if the Earth were spinning and moving around the Sun, people and objects would tend to fall off.
In the 16th century the theory was revived by Nicolaus Copernicus, in a form consistent with then-current observations. This theory resolved the issue of planetary retrograde motion by arguing that such motion was only perceived and apparent, rather than real: it was a parallax effect, as a car that one is passing seems to move backwards against the horizon. This issue was also resolved in the geocentric Tychonian system; the latter, however, while eliminating the major epicycles, retained as a physical reality the irregular back-and-forth motion of the planets, which Kepler characterized as a " pretzel."
Heliocentrism was notably advanced by Galileo, Kepler, and Newton. It was vigorously resisted, though, by elements in the Roman Catholic Church, who prevailed in showdowns in 1616 and 1633 and officially suppressed heliocentrism. The favored system had been that of Ptolemy, in which the Earth was the center of the universe and all celestial bodies orbited it. (The Catholic support for geocentricism should not be confused with the idea of a flat earth, which the Church never supported.) When prominent Catholic astronomers, including Clavius, became dissatisfied with the Ptolemaic system, many moved to the rival Tychonian system, a geocentric compromise; after 1633, the use of this system was almost mandatory. For advancing heliocentric theory Galileo was put under house arrest for the last several years of his life.
Archimedes' objection to Heliocentrism that, if it were true, parallax should be observed in the apparent positions of the fixed stars was finally put to rest when stellar parallax was observed with the greatly improved instruments of the 19th century, by which time the model of a heliocentric solar system in a very big universe was accepted by almost everyone.