ASTRON C12 Study Guide - Gravitational Energy, Milky Way, Apparent Retrograde Motion
12 Oct 2013
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Document Summary
Chapter 1; our modern view of the universe. Our place in the universe: earth orbits the sun. The sun is one of over 100 billion stars in the milky way galaxy. Our galaxy is one of about 40 galaxies in the local group. The local group is one small part of the local supercluster: which is a small part of the universe. The universe began with the big bang and has been expanding ever since, except in localized regions where gravity caused matter to collapse into galaxies and stars. The big bang produced hydrogen and helium, the rest of the elements have been produced by stars and recycled within galaxies from one generation of stars to the next i. e. we are star stuff . The age of the universe limits the extent of the observable universe. The universe is about 14 billion years old and so the observable universe extends to about 14 billion light years.
