AST— Jan 10 Lecture + Chapter Notes

5 Pages

Astronomy & Astrophysics
Course Code
Michael Reid

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ASTEstablishing Our Place in the Universe Tuesday January 10 201211Our Modern View of the Universe y Ancestors believed that heavens revolved around the stationary earth o Earthcentered or Geocentric o Belief only changed when confronted with strong evidenceWhat is our place in the universe y Earth is a planet orbiting the Sun Our Sun is one of more than 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 one small part of the Universe we live on one planet orbiting one star among more than 100 y Our cosmic addressbillion stars in the Milk Way Galaxy which in turn is one of billions of galaxies in the universe y Earth is a planet in our solar systemconsists of the Sun and all the objects that orbit ito Sun and all the collection of stars are called the Milky Way Galaxy o lanet object that orbits the star and shines by reflecting light from its star Object can only be considered a planet if it 1 orbits the star 2 is large enough for its own gravity to make it round 3has cleared most objects from its orbital path y Galaxya great island of stars in space containing millionsbillionstrillions of stars y Milky Way is one of the two largest galaxies among 40 galaxies in the Local Groupy Galaxy clustersgroups of galaxies with more than a few dozen members regions in which galaxies and galaxy clusters are most tightly packed y Superclustersy Together all these structures make up the universeo The sum total of all matter and energy encompassing the superclusters and voids everything within them How did we come to be y The universe began in the Big Bang and has been expanding ever since except in localized regions where gravity has caused matter to collapse into galaxies and stars The Big Bang essentially produced only two chemical elements hydrogen and helium The rest have been produced by stars and recycled within galaxies from one generation of stars to the next which is why we are star stuff y The Big Bang and the Expanding Universe o Observations show the universe is expandingaverage distances between galaxies are increasing with timeTherefore galaxies must have been close together y If we go back far enough we must reach the point at which 14 billion years ago expansion beganBig Bango Universe has continued to expand but on smaller size scales the force of gravity has drawn matter togethergalaxies and galaxy clusters and objects within them such as planets and stars do not expand
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