Heliocentrism and Geocentrism
- ≈ 350 BC, Aristotle
- Aristotle, a pupil of Plato, becomes the tutor of Alexander the Great.
Aristotle's views of the world shape science for centuries. His influence lasts
until the enlightenment. In his book On the Heavens (part 14),
From these considerations then it is clear that the earth does not move and does not lie elsewhere than at the centre.
- ≈ 250 BC, Aristarchus
- Aristarchus estimates the size of the sun to be much larger than the size of the earth. Based on this observation he then presents the heliocentric model.
- ≈ 250 BC, Archimedes
- In The Sand-Reckoner, Archimedes estimates the number of sand corns in the universe using the heliocentric model of Aristarchus.
- ≈ 150 AD, Ptolemy
- In his book Almagest, Ptolemy introduces so called epicycles to explain planetary motions, based on the assumption that the earth is at the centre and does not move. Almagest is considered to be one of the most influential scientific works in history.
- 1543, Nicholaus Copernicus
- Just before his death, Copernicus publishes the book De Revolutionibus Orbium Coelestium (On the Revolutions of the Heavenly Spheres) in which he places the sun rather than the earth at the centre of the universe. This book is the beginning of the Copernican Revolution.
- 1572, Tycho Brahe
- Tycho Brahe observes a star being born and publishes his observation in De nova stella. Brahe's observation refutes the commonly held view at the time, a view which dates back to Aristotle, that the stars are fix and never changing at the outskirts of the universe. Since Brahe couldn't observe a stellar parallax, he concluded that the earth did not move. He proposed a model where the planets move around the sun, and the sun moves around the earth. (It was later shown that it wasn't a star being born Brahe had observed, but the supernova SN 1572, i.e. a star exploding.)
- 1609, Johannes Kepler
- Using the observational data collected by Tycho Brahe, Johannes Kepler introduces his first two laws of planetary motion in Astronomia nova. The first law: the planets move in elliptical orbits with the sun at one focus.
- 1616, Roman Inquisition
- On 24 February 1616 a team of eleven consultants for the Roman Inquisition condemns the Copernican System, stating that the heliocentric system is “foolish and absurd in philosophy” and “formally heretical”.
- 1633, Galileo Galilei
- Galileo Galilei stands trial on suspicion of heresy "for holding as true the false doctrine taught by some that the sun is the centre of the world". At the trial he is found guilty and sentenced to formal imprisonment. Galileo spends the rest of his life under house arrest.
- 1687, Isaac Newton
- Sir Isaac Newton publishes Philosophiae Naturalis Principia Mathematica (Principia). In Principia, Newton explains Kepler's laws of planetary motion in terms of universal gravitation. Newton doesn't consider the sun to be at rest, instead he uses the center of gravity of the solar system.
- 1838, Friedrich Bessel
- Friedrich Bessel is the first to accurately measure a stellar parallax. In 1838 he announces that the star 61 Cygni has a parallax of 0.314 arcseconds.
- 1992, Roman Catholic Church
- Pope John Paul II closes a 13-year investigation into the church's condemnation of Galileo in 1633 by
declaring that Galileo was right:
Thanks to his intuition as a brilliant physicist and by relying on different arguments, Galileo, who practically invented the experimental method, understood why only the sun could function as the centre of the world, as it was then known, that is to say, as a planetary system. The error of the theologians of the time, when they maintained the centrality of the earth, was to think that our understanding of the physical world's structure was, in some way, imposed by the literal sense of Sacred Scripture.
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by Malin Christersson under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 Sweden License