StudyGuide1 - Astronomy 309R Spring 2009 Please read Hawley...

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1 Astronomy 309R – Spring 2009 3. Important ideas and concepts will be on the test, but minor facts, such as the years of birth and death of a specific historical person discussed on the textbook, will not be. Please also read the slides of Lecture 1 containing an introduction to the subject of cosmology, Lecture 2 on the early history of cosmology, Lecture 3, on momentum and gravity, and Lecture 4, on energy, stability, and the virial theorem. Particularly general and important concepts are underlined. What is cosmology? Provide and explain a descriptive definition cosmology. What are some of the questions that modern cosmology aspires to answer? What do we mean by “universe”? Our notion of what the universe is like is constrained by our technical ability to observe, measure, and quantify physical and celestial phenomena, and by our intellectual intuitions and preferences. Be prepared to give examples of what “universe” meant to thinkers and scientists in the ancient Mediterranean and in the 16 th and 17 th century Europe. (Hint: define and explain the geocentric and the heliocentric pictures of the universe.) Identify the main themes in ancient Greek (or “Hellenistic”) cosmology. Here is an outline of the main themes that we discussed in class: 1. Starting with Pythagoras, the Greeks developed the notion that simple mathematical relations describe the universe. 2. Plato thought that our perceptual experience is a shadow of reality. The true reality is composed of abstract “forms” and it can be reached by an intelligent mind, but is not directly accessible to the senses. 3. The Greeks debated what are the basic constituents of the universe: is it made of water, earth, fire, air, ether, or atoms? The Greeks contemplated how the basic constituents mixed and interacted with each other. These were philosophical arguments, without quantitative (i.e., scientific) content. 4. The Greeks discussed the origin of motion. An example is Aristotle’s idea that motion requires force and resistance. 5. The Greeks developed mathematical models for the motion and arrangement of celestial bodies (the moon, the sun, the planets, and the stars). Examples of these models are the spheres of Eudoxus, and the epicycles of Ptolemy. 6. Because of the democracy and intellectual freedom in ancient Athens, ancient Greek philosophers were able to hold different points of view and to disagree and debate with each other. What were the observations that ancient astronomers hoped to explain? Explain the origin of the apparent retrograde motion of planets. (Some planets like Mars occasionally reverse the direction of motion on the sky, when viewed against the background of distant stars. The planet appears to make a U-turn, backtrack for a while along its original orbit, make another U-turn, and continue where it had been moving on the sky prior to the first U-turn. This apparent retrograde motion is a consequence of the fact that
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This note was uploaded on 09/14/2009 for the course AST 309 taught by Professor Johnlacy during the Spring '08 term at University of Texas.

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StudyGuide1 - Astronomy 309R Spring 2009 Please read Hawley...

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