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# ASTR101_L20_post - Reminders HW#7(Ch 11 is due Friday Night...

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3/31/09 Lecture 20 Dr. Silverstone Astr101 Spring 2009 1 Lecture 20 Announcements Reminders: HW #7 (Ch 11) is due Friday Night April 3 (at midnight) Midterm #2 in one week! Tuesday April 7 Bring ScanTron answer sheet, #2 pencil, scientific calculator Review Session? Finish Reading Chapters 12,13, & 14 (Jovian Planets & moons) TEST YOUR CLICKER ! Today’s Outline: Review of Current Scores on BlackBoard Surface Temperature and Escaping Gases Chapter 15 Asteroids & Comets Kirkwood Gaps Asteroids & Meteorites Comets & Meteor Showers

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3/31/09 Lecture 20 Dr. Silverstone Astr101 Spring 2009 2 Lecture 20 Announcements 2.0 Reminders: HW #7 (Ch 11) is due Friday Night April 3 (at midnight) Midterm #2 in one week! Tuesday April 7 Bring ScanTron answer sheet, #2 pencil, scientific calculator Review Session? Study for your Midterm! Bring Questions about concepts giving you trouble to Thursday’s Class! TEST YOUR CLICKER ! Today’s Outline: Review of Current Scores on BlackBoard Surface Temperature and Escaping Gases Chapter 15 Asteroids & Comets Kirkwood Gaps Asteroids & Meteorites Comets & Meteor Showers
3/31/09 Lecture 20 Dr. Silverstone Astr101 Spring 2009 3 Current Scores on BlackBoard Maximum score = 70 (the remaining 30 comes from the Final Exam) Average = 47.6 / 70 = 68% 20% iClicker , 20% Homework , 30% Midterm(s), 30% Final Exam Red = expected # of 77 students, % in the Syllabus: A: 20%, B: 30%, C: 30%, D: 15%, F: 5%

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3/31/09 Lecture 20 Dr. Silverstone Astr101 Spring 2009 4 Calculating Surface Temperature Calculating Surface Temperature Luminosity = total energy (over all colors) in all directions Flux = energy through a specific surface area = Luminosity / (4 π r 2 ) Stephan Boltzman law (1879): Flux from a Blackbody F = σ T 4 Luminosity of the Sun L Sun = 4 π r Sun 2 σ T Sun 4 What is the “temperature” of the Sun’s light at the distance of the Earth’s orbit? 4 π r Sun 2 σ T Sun 4 = 4 π r 1AU 2 σ T 1AU 4 r Sun 2 T Sun 4 = r 1AU 2 T 1AU 4 (r Sun /r 1AU ) 2 = (T 1AU /T Sun ) 4 T 1AU /T Sun = (r Sun /r 1AU ) 1/2 T 1AU =T Sun (r Sun /r 1AU ) 1/2 T 1AU =5800K(6.86x10 5 km/150x10 6 km) 1/2 =5800K (1/219)
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