exam3reviewp - Today Exam#3 Review Exam #3 is Thursday...

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ISP209s8 Exam3 Review -1- Today – Exam#3 Review • Exam #3 is Thursday April 24th in this room, BPS 1410; Extra credit is due 8:00 am Tuesday April 29 • Final Exam is 3:00pm Monday April 28 in BPS 1410 • The exam is 40 multiple choice questions. There are two or three questions where you will have to use a formula. There are several “number” questions, like what was the initial temperature of the Big Bang (10 35 Kelvin) • Bring your student ID • You will have the full 80 minutes for the exam. • You can bring one 8.5x11 inch sheet of notes (front and back) ISP209s8 Exam3 Review -2- Relative Sizes of Stars Blue – hot Red - cooler ISP209s8 Exam3 Review -3- Hertzsprung-Russell Diagram ISP209s8 Exam3 Review -4- Blackbody Radiation All objects emit a spectrum of photons. A perfect black body has the spectrum shown at the left. The emission spectrum depends on temperature, T. The amount depends on surface area, A and temperature T. 4 2 8 4 10 67 . 5 ; K m W AT L × = = σ
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ISP209s8 Exam3 Review -5- How do stars do it? • The color of a star depends on its Temperature (blue, more hot – red, more cool) • In 5 billion years, the Sun will become a red giant and then, later, a white dwarf • Stars generate energy by fusing lighter elements into heavier elements. This is where most atoms in our bodies were made. ISP209s8 Exam3 Review -6- How did the Universe Begin? • Evidence points to the Universe beginning in a hot fireball 13.7 billion years ago. We call this the Big Bang • Evidence for the Big Bang – Expansion of the Universe – The Big Bang model correctly predicts the formation of the light elements observed to be present in the early universe (mostly hydrogen and helium). – The cosmic microwave background radiation ISP209s8 Exam3 Review -7- The structure of our local set of galaxies ISP209s8 Exam3 Review -8- Sloan Digital Sky Survey of Galaxies Earth 2000 Mly Structure: vast clusters and voids
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-9- Variable Stars – standard candles Once you find a variable star, you know how luminous it is. RR Lyrae Cepheids ISP209s8 Exam3 Review -10- A Sample Problem • Suppose star A and star B have the same luminosity. • If star A is 5 times brighter than star B, what can we say about their relative distances? • Star B is farther away a b a b b b a a b a d d d d d L d L b b d L brightness = = = = = = 5 5 4 4 4 (distance) 4 luminosity 2 2 2 2 2 2 π ISP209s8 Exam3 Review -11- Hubble Expansion • Hubble observed that on average all galaxies seem to be moving away from us. • The speed is related to distance. Galaxies farther away are moving faster • Hubble Law: • If a galaxy is observed to be moving away at 2000 km/s, we expect the galaxy is v/H 0 =100 Mly away Mly s km / 20 H distance; H velocity 0 0 = = ISP209s8 Exam3 Review -12- The Universe as we know it now Us Sun 1.6E-8 ly Nearest Star 3 ly Expand by 1,000,000 Us Local Group 3 Mly Us Edge of Universe Farthest Quasars and Galaxies 13 Bly
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exam3reviewp - Today Exam#3 Review Exam #3 is Thursday...

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