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Chapter 1

Chapter 1 - Our Place in the Universe

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Astronomy 1021
Carol Jones

September 12, 2011 Chapter 1-Our Place in the Universe 1.1O URM ODERNV IEW OF THUNIVERSE What is Our Place in the Universe? Solar System- A star and all of the objects that orbit around it The planets and their moons as well as asteroids and comets orbiting around the sun. Galaxy- A great island of stars in space, containing from a few hundred million to a trillion or more stars bound together by gravity. Milk Way Galaxy- Huge, disk-shaped collection of more then 100 million stars Local Group- The group of approximately 40 galaxies to which Milky Way Galaxy belongs. Cluster of Galaxies- A collection of a few dozen or more galaxies bound together by gravity Group of Galaxies- A few to a dozen galaxies bound together by gravity. Supercluster- The region in which galaxies and galaxy clusters are most tightly packed. (Clusters of galaxy clusters) Universe- The sum total of all matter and energy, encompassing the superclusters and voids and everything within them. How did We Come to Be? The big bang is the point when expansion began, 14 million years ago. The entire universe is still expanding while gravity pulls matter together to make galaxies. The average distance between galaxies is increasing with time. The early universe contained only two chemical elements (hydrogen and helium). Other elements were made by stars and recycled from one stellar generation to the next within galaxies. 1) Gravity compresses material in a cloud to a high enough density and heat that there is enough energy to generate nuclear fusion, the process in which lightweight atomic nuclei smash together to fuse to make heavier nuclei. 2) Stars live as long as it can shine with energy from nuclear fusion. 3) Stars die when the usable fuel is used up. Early universe only contained hydrogen, helium and a trace of lithium. Elements were created by: – the nuclear fusion that makes stars shine – through nuclear reactions accompanying the explosions that end stars’ lives Discovering the historical universe Looking at light from distant stars and galaxies is looking into the past The farther away we look in distance, the further back we look in time. Light travels 300 000km per second Light from the stars takes years to reach us Measure distance to stars in light-years (1 year = 10 trillion kilometers) We will never be able to see beyond the observable universe: the portion of the entire universe that we can potentially observe Anything beyond 14 bill
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