Chapter 34 WInter 2011

Chapter 34 WInter 2011 - Chapter 34 Cosmology: The history...

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Unformatted text preview: Chapter 34 Cosmology: The history of the Universe Did you read Chap. 34? a) Yes b) No Cosmology: The History of the Universe This semester I attended ___ of lectures A. 100% B. 90-99% C. 75-89% D. 50-74% E. Less than 50% This semester I read the chapter before lecture ___ of the time A. 100% B. 80-99% C. 60-79% D. 30 - 59% E. 0 29% A red star is brighter than a blue star. Assuming they are both main sequence stars, you can conclude that a) The blue star is closer to the Earth b) The red star is closer to the Earth c) The blue star is bigger d) The red star is bigger e) Red and blue make purple Elliptical Galaxies Old, dying stars. Little new star formation . Spiral Galaxies Mature, vital stars. Lots of star formation. Barred Spirals Its thought that our Milky Way is one of these. Irregular/Peculiar But how might one measure distance when you cant use triangulation? Distances s Locating objects in the sky is easy. Finding their distances is a nightmare! Star: 10 light yrs Galaxy: 500,000,000 light yrs Quasar: 5,000,000,000 light years How far away are all these things? s Radar and Laser Ranging Useful for things in the Solar System s Triangulation Useful for stars within ~100 light years of Earth s Brightness Comparisons Christian Huygens experiment How far away was the star called Sirius? Huygens measured the diameter of Sirius to be 1/28,000 the size of the Sun Imagine: s You have two light sources: A single white Christmas tree light A 250 Watt halogen flood light s If the flood light is far enough away, it can look like the nearby Christmas tree light. s The amplitude or intensity of the light decreases with distance. s So, unless I know something else about the light sources (i.e. how far away they are, what produces their light, the kind of bulbs they are, etc), I can only measure their apparent brightness. In the context of astronomy s Are these stars the same distance away but differ in brightness? s Are these stars of the same brightness (intensity) but at different distances from me? s Absolute brightness: How bright the star really is. It is a measure of how much energy the star puts out. s Apparent brightness: How bright the star appears to us on earth. It is a measure of the intensity of the light as it reaches earth....
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Chapter 34 WInter 2011 - Chapter 34 Cosmology: The history...

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