Sections 3.3-3.5.docx

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University of Toronto St. George
Astronomy & Astrophysics
Michael Reid

Reading Sections 3.3, 3.4, 3.5 Section 3.3 Copernican Revolution Section 3.4 Nature of Science -Type of tentative explanation, or hypothesis, is sometimes called an educated guess -Pseudoscience, which literally means “false science” -Science ultimately provides a means of bringing people to agreement -When a powerful yet simple model makes predictions that survive repeated and varied testing, scientists elevate its status and call it a theory Section 3.5 Astrology -Basic tenet of astrology is that the apparent positions of the Sun, Moon, and planets among the stars in our sky influence human events Copernican Revolution -Is the story of origin modern science Copernicus -Decided to try Aristarchus’ Sun-centered idea -He discovered simple geometric relationships that allowed him to calculate each planet’s orbital period around the Sun and its relative distance from the Sun in terms of the Earth- Sun distance -He had held fast to the ancient belief that heavenly motion must occur in perfect circles- this incorrect assumption forced him to add numerous complexities to his system to get it to make decent predictions Tycho -Proved that the nova was much farther away than the Moon -He was convinced that planets must orbit the sun -He set about compiling careful observations of stellar and planetary positions in the sky -He was convinced that the planets must orbit the sun but his inability to detect stellar parallax led him to conclude the Earth must remain stationary Kepler -Believed that planetary orbits should be perfect circles -His key discovery was that planetary orbits are not circles but instead are a special type of oval called an ellipse -The locations of the two tacks are called foci of the ellipse -The long axis of the ellipse is called major axis, each half of which is called a semimajor axis -The short axis is called the minor axis -Eccentricity is a quantity that describes how much an ellipse is stretched out compared to a perfect circle- a circle ellipse with zero eccentricity a
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