Astro Midterm 1 notes - Midterm 1(lectures 1-3 Pages 1-34...

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Midterm 1 (lectures 1-3) Pages 1-34: Early Greek science: Thales (philosopher) asked: What is the universe made of? - he thought the universe consisted of water and that the earth was a flat disk on an infinite ocean Plato and his student Aristotle carried out studying but Greeks focused more on thought and intuition rather than carrying out experiments Three things that lead to Greeks paving the way for modern science: 1) They worked communally, debating and testing each other’s proposals and challenging every new idea virtually still remains a distinguishing feature. 2) The Greeks used geometry and without it, they would not have gone far in their attempts to make sense of the cosmos and the use of math to explore new ideas is still used today. 3) The Greeks understood that an explanation about the world cant be right if it doesn’t agree with observed facts. Discarding explanations that don’t work is a crucial part of modern science. The Geocentric Model: - The Greeks constructed conceptual models of the universe to explain what they observed - Anaximander said that the heavens must form a sphere (celestial sphere) around the earth - He also discovered that the way the sky varies with latitude, earth is curved - Greek philosophers came up with a geocentric model of the earth with the earth in the middle of a great celestial sphere The Mystery of Planetary Motion: - seven day week is because seven planets are visible - the sun completes a circuit around the celestial sphere each year and the Moon completes a circuit in about a month - apparent retrograde motion: planets go backwards and this can last from a few weeks to a few months - Ptolemaic model: planets moving around Earth on small circles that turned around larger circles An Alternative Model: - Aristarchus suggested that the earth goes around the sun - His ideas were inconsistent with observations of stellar positions in the sky - Stellar parallax: annual shifts in stellar positions are proof that the Earth goes around the sun
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Greeks on the Possibility of Life Beyond Earth - Atomists: earth and heavens were made from an infinite number of individual atoms of each of the four elements - Aristotelians: the four elements were confined to the realm of Earth while heavens were made of a fifth element called aether or the quintessence 1.2 – The Copernican Revolution How did it further the development of science? - 1953, Nicholas Copernicus published De Revloutionibus Orbium Coelestium which revived Aristarchus’s radical suggestion of a sun-centered solar system and described the idea with math detail - the problem came because he believed that heavenly motion must occur in perfect circles and his complete model was not accurate in the end Tycho - he built naked eye observatories and over 3 decades, he used them to measure planetary positions to within in minute of an arc Kepler - Joannes Kepler was hired by Tycho - He believed that planetary orbits should be perfect circles - He discovered his predicted positions differed by Tycho’s by only about 8
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