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Lecture04

# Lecture04 - Astro Nova Earth and Mars dodge...

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Astro Nova Earth and Mars dodge bullets (politicians don’t) Asteroid 2007 WD5 missed Mars last night Asteroid 2007 TU24 missed Earth on 1/29 1.5 x lunar distance 1,500 megaton potential Explorer I 50 th anniversary RU astronomer announces discovery of baby galaxies E. Gaweiser, C. Gronwall (PSU) 1/10 size, 1/20 mass of Milky Way “fossils” from 12 billion years ago

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Previous Lecture Stellar Brightness Wave nature of light c = f λ Spectrum: intensity as a function of wavelength Photometric filter system: UBVRI Luminosity, Flux, and Inverse-Square Law F = L / (4 π d 2 ) Thermal sources and the blackbody spectrum Wien’s law: λ max 1 / T Stefan-Boltzmann Law: L = 4 π R 2 σT 4
Quiz Question 1 “Roses are Red, Violets are Blue”. What does this mean? A. Roses are hotter than violets. B. Roses are cooler than violets. C. Roses absorb more blue light, violets absorb more red light. D. Roses reflect more blue light, violets reflect more red light. E. It’s poetic license

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Quiz Question 2 Star A has luminosity equal to that of the Sun. Star B has 4 times the luminosity of the Sun. Observed from Earth, the stars have equal apparent brightness. This means that: A. This is impossible Star B must appear 4 times brighter than Star A. B. The two stars are at the same distance. C. Star B is 4 times further away than Star A is. D. Star B is 2 times further away than Star A is. E. Star A is 4 times further away than Star B is.
Quiz Question 3 Suppose that I increase the electrical current flowing through an incandescent light bulb. What will happen? A. Nothing, until the bulb explodes. B. The bulb will get brighter, but remain the same color C. The bulb will remain the same brightness, but its color will become bluer D. The bulb will get brighter, and its color will become redder. E. The bulb will get brighter, and its color will become bluer.

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The Doppler Effect Approaching sources squeeze wavefronts together, producing a blueshift Receding sources stretch wavefronts out, producing a redshift For low speeds: The Doppler shift measures only the radial (line-of-sight) component of velocity http://www.kettering.edu/~drussell/Demos/doppler/doppler.html c v
Homework Question FBQ 2: Use Figure 16.5 to find the number of stars of absolute magnitude 6 compared to those of absolute magnitude 13.

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