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## INST 2403 The Expanding Universe

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**INST 2403The Expanding Universe**Dr. Uwe Trittmann Utrittmann@Otterbein.edu Office: Science 106 Phone: 823-1806 Secretary: Sandy Sallee (823-1316), Science 308 Office Hours: M 3-4pm, W 4-5pm or by appointment.**Course Materials**• Textbooks: • Astronomy: A Beginner’s Guide to the Universe, 6thEdition, by Chaisson and McMillan (Prentice Hall) • Lecture Tutorials for Introductory Astronomy, 2nd ed., by Edward E. Prather, Tim P. Slater, Jeff Adams, and Gina Brissenden (Benjamin Cummings, 2007) • Need to buy WebAssign access, too! • Observatory schedule, lecture notes, study guides, the syllabus, notices, online resources, …**Assignments and Grading**• Homework (20%) • Skylab (13%) • Rooftop Visit + Essay (2%) • Group discussions & Activities (8%) • Constellation Quiz (7%) • Three In-Class tests (each 10%) • Final exam (20%) [comprehensive!]**Homework**• We will use WebAssign, an online homework system • Procedure different than described in syllabus • You need/have already a WebAssign access card**Skylab**• Equivalent of a term paper, but more experimental • 5 different experiments, or one simulated experiment • You can work in groups of up to 4 on the Skylab • Start early - weather is always a factor • Ask questions! • Due May 7, first draft February 24 (strict deadlines!)**A Glance at this Class**• The whole universe in 14 weeks! • Expect to work at least as hard for this course as for your major classes • The focus is on concepts, not facts; on the methods and tools of science: • How do we know? • How can we measure it? • How can we predict it?**Science and Quantitative Reasoning**• Without quantitative reasoning there is no progress in science (Galileo) • However, (quantitative) reasoning is also very useful in everyday life • Interest rate, gas mileage, buying a used car, that guy from Nigeria…**Making Sense of Numbers**• Need to know how to read graphs, functions • Want to compare to relevant scale choose convenient units • Underlying concepts have to be clear • There is evidence that the disconnect between scientists and the public starts at simple concepts, like area, volume, ratios and graphs • We’ll start there and we’ll move up to the stars!**Example: Relevant Scales**• The mass of the Earth is 6 x 1024 kg • This number can be used in equations easily • Nobody has a sense of how heavy that is • Need to compare to relevant scales • Mass of Sun: 2 x 1030 kg Sun’ mass = 300,000 Earth masses • Mass of Jupiter: 2.4 x 1027 kg 300 Earth mass = 1 Jupiter mass • Mass of Venus: 4.7 x 1024 kg 1 Venus mass =1 Earth mass • Relevant Scale: 1 EM = 1 Earth mass**Example II**• The radius of the Earth is 6 x 106 m • Convert to miles (1mile = 1600m): 3800 miles • That is something we can fathom • But: use it to get insight!**Insight from Numbers**• We know ANY volume SCALES like the radius to the third power • Volume of Earth: 63 x (106) 3 m3 = 216 x1018 m3 = 1 EV • Sun (radius 7 x108m): 1.5 million Earth Volumes • But: only 300,000 times the Earth mass! • Conclusion: the Sun is made from material that is 5 times lighter than the stuff the Earth is made of!**Getting a sense of how things are working by using**(quantitative) analysis • Analyzing things meaning breaking down complicated stuff we cannot understand into smaller and smaller pieces, until we can solve the little problems, then piece them together again.**Asking questions to ask questions**• Scientists often come off as pretending to know everything (Sheldon) • In fact, they have a healthy self-confidence that they can at least say something about everything • Why? They simplify things enough to make a rough estimate, then compare to reality • Correct? Hah! I was right! • Not correct? How interesting! We can explore more!**How many people live in Australia?**• No idea. • Say something: • Can get size of this continent • Know size & inhabitants of USA • Proportionality tells us there should be XX million Australians • Conclusion: there are much fewer! • Next Question: Why?**Chase the Demons Away (Sagan)**• The uninitiated tends to thinks things are much more complicated than they are • Tip of the iceberg • There is nothing mysterious about the natural world! You can! …understand it, do it, calculate it, ask relevant questions**The most important graph: 1/r2**• Force of gravity (and EM) falls off like that • Brightness of stars goes down like that • Simple reason: • things spread out over a sphere • dilutes over the surface of the sphere • surface scales like r2**Example: Two 100W light bulbs**• One APPEARS nine time brighter than the other. How far away is it? • We can’t compute how far away it is in absolute terms, but it must be √9=3 times farther than the other one. • Which one is brighter?**Appearances**• Don’t be fooled by appearances! • The sun and the moon appear to be the same size in the sky (0.5 degrees) • Alpha Centauri appears to be much dimmer than the Sun • Alpha Centauri and Vega appear to be equally bright**Think!**• The moon and the sun COULD be at different distances • Alpha Centauri and Vega COULD be different types of stars**Find out = Measure!**• How? • That’s where the game of science starts!**The most important measurement in Astronomy: Distance!**• The distances are astronomical! • The distance scales are very different • Solar system: light minutes • Stars: light years • Galaxies: 100,000 ly • Universe: billions of ly • Need different “yardsticks”**Yardsticks and the Expanding Universe**• Realizing (measuring) the distances to objects means realizing how big the universe is: • We realized that the solar system is not the universe • We realized that our galaxy is not the universe • We realized that the universe is not static