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Astronomy & Astrophysics
Clifford Orwin

Our place in the Universe(Chapter 1) Geocentric - Cannot feel the constant motion of Earth as it rotates on its axis and orbits the sun Cosmic Address - Our place in the universe Solar System (e.g.. Earth) - Consist of the sun and all the objects that orbit it (planets, their moons and smaller objects including rocky asteroids and icy comets). Milky Way Galaxy - disk shaped collection of stars (100 billion stars) - 1 of the 2 largest among the 40 galaxies in the LOCAL GROUP Galaxy - island of stars (few 100 million to trillion or more stars) Galaxy Clusters - galaxies with more than a few dozen members (very dense) - arranged in giant chains with huge voids between them SuperClusters - area where galaxies and galaxy cluster are most tightly packed Asteroid - small rocky object that orbits a star. Part of a category called small solar system bodies Comet - Small ice rich object that orbits a star. Part of a category called small solar system bodies - Our solar system is located a little more than halfway from the galactic center to the edge of the galactic disk. Denition of of OUR UNIVERSE: - Sum total of all matter and energy, encompassing the supercluster and voids and everything within them. Our Place in the UNIVERSE: - We live on a planet orbiting and avg. star among more then 100 billion stars in the Milky Way Galaxy. Big Bang (the rate at which galaxies are moving apart) and Expanding Universe - The Universe is expanding----the avg. distance between galaxies is increasing in time - Expansion began 14 billion years ago - Force of gravity has drawn matter together causing matter within to clump together resulting into galaxies and galaxy clusters Stars and planets are formed by: - collapse of clouds of gas and dust
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