Astronomy Test #3 IMPORTANT THINGS Crossword
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
                                                          
 
 
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Down: 2) Days of the week were named for the Sun, Moon, and visible planets. (study power point as well)3) • Tycho thought he had measured stellar distances, so lack of parallax seemed to rule out an orbiting Earth. • Galileo showed stars must be much farther than Tycho thought—in part by using his telescope to see that the Milky Way is countless individual stars. • If stars were much farther away, then lack of detectable parallax was no longer so troubling. 4) The most sophisticated geocentric model was that of Ptolemy (A.D. 100–170)— the Ptolemaic model: • Sufficiently accurate to remain in use for 1500 years • Arabic translation of Ptolemy’s work named Almagest (“the greatest compilation”)5) Copernicus proposed the Sun-centered model (published 1543). • He used the detailed model to determine the layout of the solar system (planetary distances in AU). But . . . • The model was no more accurate than the Ptolemaic model in predicting planetary positions, because it still used perfect circles. 9) 1. As a planet moves around its orbit, it sweeps out equal areas in equal times. 2. This means that a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.10) Measures the size of the Earth (c. 240 B.C.) MEASUREMENTS: Syene to Alexandria: 1. Distance= 5000 stadia 2. Angle: 7D. Calculate Circumference of Earth: 7/360 x (circum. Earth)=5000 stadia ---> circum. Earth = 5000 x 360/7 stadia = 250,000 stadia Compare to modern value (= 40,100km): Greek stadium = 1/6 km => 250,000 stadia = 42,000 km 11) An ellipse looks like an elongated circle. Across: 1) Galileo’s experiments showed that objects in air would stay with a moving Earth. • Aristotle thought that all objects naturally come to rest. • Galileo showed that objects will stay in motion unless a force acts to slow them down (Newton’s first law of motion).6) STUDY VIA POWER POINT (GVOKTL)7) • The word theory has a different meaning in science than in everyday life. • In science, a theory is NOT the same as a hypothesis. • Ascientifictheorymust: — Explain a wide variety of observations with a few simple principles — Be supported by a large, compelling body of evidence — NOT have failed any crucial test of its validity8) = circles upon circles 12) • Tycho’s observations of comet and supernova already challenged this idea. • Using his telescope, Galileo saw: — Sunspots on the Sun (“imperfections”) — Mountains and valleys on the Moon (proving it is not a perfect sphere)13) 8 years14) • Brahe compiled the most accurate (1 arcminute) naked eye measurements ever made of planetary positions. • He still could not detect stellar parallax, and thus still thought Earth must be at the center of the solar system (but recognized that other planets go around the Sun). • He hired Kepler, who used Tycho’s observations to discover the truth about planetary motion.15) • Kepler first tried to match Tycho’s observations with circular orbits. • But an 8-arcminute discrepancy led him eventually to ellipses.16) Science progresses through the creation and testing of models of nature that explain the observations as simply as possible. (Simplicity = “Occam’s razor”)17) Modern science seeks explanations for observed phenomena that rely solely on natural causes. (A scientific model cannot include divine intervention.)18)  Solar day = 24 hours (rotation + orbit about the Sun) • Sidereal day (Earth’s rotation period) = 23 hours, 56 minutes 19) The orbit of each planet around the Sun is an ellipse with the Sun at one focus. (1. Perihelion 2. Aphelion) (look at it via power point)20) More distant planets orbit the Sun at slower average speeds, obeying the relationship p2 = a3 p = orbital period in years a = average distance from Sun in AU 21) of all phases of Venus proved that it orbits the Sun and not Earth (Venetian’s view of Earth?). 22) a generally well established scientific theory or set of theories 23) Galileo (1564–1642) overcame major objections to the Copernican view. Three key objections rooted in the Aristotelian view were the following: 1. Earth could not be moving because objects in air would be left behind. 2. Noncircular orbits are not “perfect” as heavens should be. 3. If Earth were really orbiting Sun, we’d detect stellar parallax.
 

 

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