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phys0001_chapter04 - Chapter 4 Brief History of Astronomy...

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Chapter 4 Brief History of Astronomy Among other things, history tells us who is right and who is wrong. We will concentrate on the "rights", but the "wrongs" will show us why the "rights" are correct. The Early Development of Astronomy Each culture has its own stories about the sky and the stars. In ancient China, people generally believed that the sky or the heaven was important but mythical. Hence, there were serious and detailed observational records, but no significant models for predictions. In contrast, around 600 B.C., Greek philosopher Thales of Miletus had already proposed the universe is rational and could be understood by humans. Around 400 B.C., Plato claimed that heaven is perfect and circle is the most perfect form. Thus, the heaven is in uniform circular motion with the Earth at the center. This is the beginning of the geocentric model . The simple geocentric model cannot explain the retrograde motion of the planets. Around 140 A.D., Ptolemy proposed his refined geocentric model. (He proposed many refinements. We only talk about the simplest one.) In the Ptolemaic universe, planet moves in a small circle called an epicycle , and the center of the epicycle moves along a larger circle around the Earth. The centers of the epicycles of Mercury and Venus must lie on the line joining the Earth and the Sun. Stars are fixed on an outermost sphere. This model gives predictions on the positions of the planets within a few degrees from the actual positions. This was generally accepted and the Ptolemaic model dominated the western world for about 1500 years.
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Copernicus Nicolaus Copernicus (1473-1543) proposed the heliocentric model
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phys0001_chapter04 - Chapter 4 Brief History of Astronomy...

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