INST 2403 The Expanding Universe

Dr. Uwe Trittmann Office: Science 106 Phone: Secretary: Celina Chou ( ), Science 308 Office Hours: MW 2-3pm or by appointment.

Course Materials Textbooks: –Astronomy: A Beginner’s Guide to the Universe, 7th Edition, by Chaisson and McMillan (Addison-Wesley 2012) –Lecture Tutorials for Introductory Astronomy, 3rd ed., by Edward E. Prather, Tim P. Slater, Jeff Adams, and Gina Brissenden (Benjamin Cummings) –Need to buy WebAssign access, too!WebAssign Course Web Page: Observatory schedule, lecture notes, study guides, the syllabus, notices, online resources, …

Assignments and Grading Rooftop Visit + Essay2% Activities8% (total) Participation5% Constellation quiz6% Just-in-time responses5% Homework12% iSkylab12% (total) 3 in-class tests10% each30% Final exam (comprehensive!)20%

Daily Homework & Warm-Ups Before class (8am): answer warm-up questions online about reading for the day – ls/WarmupDB/Astronomy_Section_1http://neutrino.otterbein.edu/~tagg/Courses/Too ls/WarmupDB/Astronomy_Section_1 After Class: use WebAssign, an online homework system daily!WebAssign –Password & username: first initial plus last name all lowercase, e.g. utrittmann

iSkylab Equivalent of a term paper, but more experimental 4 different stages Start early - weather is always a factor Ask questions! Due Feb 26, March 31, April 23, May 9

Keep in mind that this course … –is part of your quest for education –costs (you) a lot of money –is a university, not high school, course –can qualify you for getting an interesting job

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; 2hrs out of class per class 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?

Teaching Philosophy Teaching is merely an invitation to learn You have to learn yourself! Operational instead of Declarative Knowledge Peer instruction Class discussions Participation (Credit!) –Must engage with the material

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 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 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 kg  Sun’ mass = 300,000 Earth masses –Mass of Jupiter: 2.4 x kg  300 Earth mass = 1 Jupiter mass –Mass of Venus: 4.7 x kg  1 Venus mass =1 Earth mass Relevant Scale: 1 EM = 1 Earth mass

Example II The radius of the Earth is 6 x 10 6 m Convert to miles (1mile = 1600m): 3800 miles That is something we can fathom Now: use it to get insight!

Insight from Numbers We know ANY volume scales like the radius to the third power Volume of Earth: 6 3 x (10 6 ) 3 m 3 = 216 x10 18 m 3 = 1 EV Sun (radius 7 x10 8 m): 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!

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!

Example: How many people live in Australia? No idea. But: Need to 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?

Don’t be fooled by what you see! 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 YOU could be upside down! The apple COULD attract the Earth with the same force  Expand your universe!

Top Down The Universe is accelerating its Expansion –How do we know? Supernovae are dimmer than they should be in a standard expanding universe –What is a supernova? What is a standard universe? SN are massive stars exploding at the end of their lives –How do we know?

Top Down Stars are hot gas balls that fuse H to He; they run out of fuel –How do we know? Can measure spectra, compare to the sun –What is a spectrum? How does the sun “work”? The sun is 300,000 more massive than the earth, consists of H & He, produces a lot of energy  must be fusion –How do we know?

Top Down Measure distance to sun, use Newton gravity to obtain mass, measure H & He spectra in lab –How do we measure distance to sun? –What is Newton gravity? –What are spectra in the lab? Use Kepler’s laws, observe special configuration of planets from different positions on earth –What are Kepler’s laws? How big is Earth?

Top Down Planets go around the sun in ellipses –How do we know? The observer’s view is different for different places on Earth  radius –How do we know? Go out and look at the sky!