lecture14 - Astronomy 3 The Nature of the Universe...

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Astronomy 3: The Nature of the Universe Professor Alice Shapley Lecture 14: Stellar Life Cycles (NGC 1499 Image credit: Markus Noller, Deep Sky Images)
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Logistics Quiz #7: due Monday, May 23rd, 10 pm. Available at CCLE website https://ccle.ucla.edu/course/view/11S-ASTR3-2 Structure and Motion of Spiral Galaxies.” Issue with lab #5 grading for people in Cory’s sections (2D and 2E). Please come see me or one of the other TAs.
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Midterm #2 Results Exam graded out of 50 points. • Median score (i.e. halfway point): 39/50 (78%), mean=38.6 (77.2%). • Midterm scores and solutions posted on-line after class. Come to me with questions.
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Midterm #2 Results 3 Hardest questions: We’ve talked about how many Suns could fit within the distance separating Earth and the Sun (i.e. within one astronomical unit). How many Earths could fit within 1 astronomical unit? a) ~10 b) ~100 c) ~1000 d) ~10,000 e) ~10 6 The radius of Earth is ~0.01 x the radius of the Sun.
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Midterm #2 Results 3 Hardest questions: Which internal energy source produces heat by converting gravitational potential energy into thermal energy? a) accretion b) differentiation c) radioactivity d) both (a) and (b) e) all of the above
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Midterm #2 Results 3 Hardest questions: A sphere with a radius of 2 meters has a surface-area-to-volume that is times as large as the surface-area-to-volume of a sphere with a radius of 4 meters. a) 1 b) 2 c) 4 d) 1/2 e) 1/4 Recall: SA=4 π r 2 . V=(4/ 3) π r 3 . SA/V=3/r. So, SA/V(2)= 3/2, while SA/V(4)=3/4. So, SA/V for 2-meter radius sphere is twice as large as that for 4-meter radius sphere.
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Review from Last Time Measurements of stars: Luminosity, flux, distance – Temperature Mass (use binary stars to weigh them!), masses range from 0.08 to ~100 times the mass of the Sun.
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1) Hotter objects emit more light at all wavelengths Stefan-Boltzmann Law: Luminosity per square meter = constant x T 4 2) Hotter objects emit light at shorter wavelengths (higher frequencies) Wien’s Law: T (K) = 2,900,000/ wavelength (nm) Laws of Thermal Radiation
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Lines in a star’s spectrum correspond to a spectral type that reveals its temperature. Spectral type (letter/number) is shorthand for temperature. (Hottest) O B A F G K M (Coolest) STELLAR SPECTRA Hottest stars Coolest stars Letters (A-O) assigned over 100 years ago before temperatures were known. Had to be re-ordered to make sense. Still a useful aid to memory. Hottest stars: ~50,000 K Coolest stars: ~3,000 K
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Types of Binary Star Systems Visual Binary Eclipsing Binary Spectroscopic Binary NOTE : About half of all stars are in binary systems GRAVITATIONALLY BOUND STARS. • Two stars orbiting each other = BINARY. • Binary Stars yield Stellar Masses by Newton’s form of Kepler’s 3 rd Law. (Animation courtesy Richard Pogge, OSU)
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Review from Last Time Measurements of stars: Luminosity, flux, distance – Temperature Mass (use binary stars to weigh them!), masses range from 0.08 to ~100 times the mass of the Sun.
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