Early Models of the Universe
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The document summarizes several historical models of the universe: 1) Eudoxus of Cnidus proposed a geocentric model in the 4th century BC with concentric spheres and the first systematic explanation of planetary motion. 2) Aristotle also proposed a geocentric model, believing Earth was stationary at the center and composed of four elements. 3) Aristarchus proposed the first heliocentric model in the 3rd century BC, placing the Sun at the center with the Earth and planets orbiting it. 4) Ptolemy proposed a refined geocentric model in the 2nd century AD explaining planetary motions with epicycles and deferents. 5) Copernicus published his he
Early Models of the Universe
- 3. Eudoxus Of Cnidus One of the best mathematicians and astronomers of the Plato era, EUDOXUS OF CNIDUS around 400 B.C devised the system o concentric spheres and gave the first systematic explanation of the movements of the sun, the moon and the planets, emphasizing once again the ancient Greek’s insistence in the spherical perfection .
- 5. Aristotle Aristotle somehow patterned his model to the model of Eudoxus. Aristotle’s model of showed that the universe was spherical and finite. Just like Eudoxus, he perceived Earth was at the center of the universe and was stationary. He believed so because Earth is too big to move; thus, it could not rotate. Aristotle believed that Earth was composed of four elements; Earth, Water,Air and Fire. TAKE NOTE: Both models of Eudoxus and Aristotle were considered Geocentric. This means that both astronomers believed that Earth was at the center of the universe.
- 7. Aristarchus Aristarchus (BCE-230 BCE) was a Greek astronomer who made the first attempt to create a Heliocentric Model, which places the sun at the center of the Universe. He proposed that the sun and the fixed stars were at rest, while Earth revolve around the sun in a circular path.
- 9. The only work of Aristarchus that survived was entitled On The Sizes And Distances Of The Sun And The Moon. In this book, Aristarchus calculated the sizes of the sun and the moon and their distances from Earth by estimating the relative angles of the moon and the sun from the Earth. He had three assumptions a) Earth was Spherical b) It is far from the sun c) Moon passes through Earth’s shadows when they align
- 10. Claudius Ptolemaeus (Ptolemy) In this model, it is assumed that Earth was at the center of the universe, while the other celestial bodies revolved around Earth in perfect circles with constant velocity. Ptolemy’s model was considered more refined than the previous Geocentric models because his model could explain the motion of the celestial bodies accurately. Ptolemaic Universe
- 11. Ptolemy (100-AD-178 AD) assumed that the planets revolve on epicycles (small spheres) which moved around the deferent (large sphere). He added that the stars belonged to the celestial sphere which was located beyond the planetary spheres.
- 12. The center of the deferent is called the eccentric. What Ptolemy did next was to “move” Earth from its original position to a position below the center of the system that is still inside the deferent.
- 13. Nicolaus Copernicus During the 16th Century, Copernicus (1473-1543), a polish astronomer, received the heliocentric model of Aristarchus. He was afraid of condemnation. Because of this, it took him a long time to publish his work. His works were only published a year before his death. Copernicus strongly believed in the heliocentric model because there were loopholes in the Ptolemaic model in terms of predicting the positions of the planets. a. Heavenly bodies exhibited constant circular and perpetual motion along their epicycles b. The sun was at the center of the universe c. The order of the planets from the sun is Mercury, Venus, Earth (and moon) Mars, Venus, Saturn and beyond the planets were the fixed stars.
- 15. Tycho Brahe Tycho Brahe (1546-1601) was a Danish astronomer who also made planetary observation. Unlike Copernicus, Brahe believed in a geocentric universe, but his idea of the geocentric universe is slightly different from Ptolemy’s.
- 16. In Brahe’s model of the universe, called the Tychonic System, earth was at the center and the sun and the moon revolve around it, and all the other planets orbited the sun. Such a model was a type of the geoheliocentric system.