Chapter 14 The Universe: Notes

# Chapter 14 The Universe: Notes - Chapter 14 The Universe:...

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Chapter 14 The Universe: Notes 1. absolute magnitude – Used to calculate the brightness that stats would appear to have if they were all at a defined, standard distance (32.6 light-years). The brightness of a star at this distance is called absolute magnitude. This is an expression of luminosity. The sun has has an absolute magnitude of -26.7 because it is the closest star. If viewed from a standard distance the sun would have +4.8 absolute magnitude, which is about the brightness of a faint star. 2. apparent magnitude – Stars generate their own light, but some appear brighter than others. This could be due to (1) the amount of light produced by the stars, (2) the size of each star, or (3) the distance to a particular star. These combinations are responsible for the brightness of a star as it appears in the night sky. Apparent magnitude is a classification scheme for different levels of brightness. This is based on a system established by a Greek astronomer over two thousand years ago. Hipparchus hub made a catalog of the stars and assigned a numerical value to each to identity its relative brightness. The scale goes from 1-6. 1 being the brightest and 6 being the faintest. 3. big bag theory – This is the current model used to understand how galaxies form and how the universe was created. In this model the universe had an explosive beginning. According to this theory, all matter in the universe was located together in an arbitrarily dense state from which it began to expand, and expansion that continues today. Evidence that supports this (1) present-day microwave radiation from outer space, (2) current data on the expansion o f the universe, (3) the relative abundance of elements that were altered in the core of older stars – this agrees with predictions based on analysis of the big bang and, (4) the Cosmic Background Explorer (COBE) spacecraft which studied diffuse cosmic background radiation to help answer such questions as how matter is distributed in the universe, whether the universe is uniformly expanding, and how and when galaxies first formed. Initial evidence came from Edwin Hubble and his earlier work with galaxies. He was able to determine distances to some of the galaxies that had red shifted spectra. It was known that these galaxies were moving away because of the expansive redshift. This same expansion was seen in all directions meaning that the universe is expanding uniformly. This evidence points to a common beginning, a time when all matter in the universe was together. 4.

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## This note was uploaded on 02/09/2011 for the course PSC 1121 taught by Professor Tulsian during the Spring '11 term at Daytona State College.

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Chapter 14 The Universe: Notes - Chapter 14 The Universe:...

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