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PHYS 183 (51)
Tracy Webb (12)
Chapter 1

Chapter 1

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PHYS 183
Tracy Webb

1: Our Place in the Universe 1.1 Our Modern View of the Universe  star: a large, glowing ball of gas that generates heat & light through nuclear fusion in its core  planet: a moderately large object that orbits a star & shines primarily by reflecting light from its star  moon (satellite): an object that orbits a planet  asteroid: a relatively small and rocky object that orbits a star  comet: a relatively small and ice-rich object that orbits a star  small solar system body: an asteroid, comet or other object that orbits a star but is too small to qualify as a planet or dwarf planet  natural to assume we live in an earth-centred (geocentric) universe  orbits the sun (a star)  solar system: the sun and all objects that orbit it (planets, their moons, other smaller objects ie/ asteroids & comets)  star system: a star and any planets and other materials that orbit it  galaxy: a great island of stars in space containing a few hundred million to a trillion stars all held together by gravity and orbiting a common centre; scattered throughout space; some isolated, others in groups  Milky Way Galaxy: relatively large galaxy containing more than 100 billion stars; the galaxy that we live in; one of the two largest among 40 galaxies in the local group  galaxy cluster: groups of galaxies with more than a few dozen members bound together by gravity  supercluster: regions in which galaxies and galaxy clusters are most tightly packed  clusters of galaxy clusters  universe: sum total of all matter and energy  The Big Bang and the Expanding Universe o entire universe is expanding  average distances between galaxies are increasing with time o galaxies must have been closer together in the past o occurred 14 billion years ago o universe continues to expand since Big Bang  on smaller scale since gravity pulling objects together o universe continues to expand but individual galaxies & galaxy clusters do not o as the universe expanded, matter clumped into galaxies & galaxy clusters  stellar lives and galactic recycling o gravity collapses clouds of gas & dust to form stars & planets o stars not living but go through life cycles o born when gravity compresses material in a cloud to point where centre dense enough & hot enough to generate energy by nuclear fusion o nuclear fusion: process in which lightweight atomic nuclei smash together and fuse to make heavier nuclei o star “lives” as long as it can shine with energy from fusion & dies when fuel exhausted o massive stars die in titanic explosions (supernovae) o returned matters mixes with floating matter to become new clouds that stars can form from  stars manufacture the elements of earth & life o early universe only contained hydrogen & helium + traces of lithium o other elements (carbon, nitrogen, oxygen, iron) manufactured by stars  nuclear fusion or nuclear reactions accompanying explosions that end stellar lives o solar system formed 4.5 billion years ago & earlier generations of stars had already converted 2% of H & He into heavier elements  enough to make small rocky planet  know stuff about the past by studying light from distant stars & galaxies o light travels 300 000 km/s  takes more than 1 second to reach earth from the moon; 8 minutes from the sun
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