AST101 - Chapter 1 Study Notes

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Astronomy & Astrophysics
Michael Reid

11 Our Modern View of the Universe Milky Way Galaxycontains more than 100 billion starsour solar system is located half way from the galactic enter to the edge of the galactic diskour Milky Way is one of the largest among 40 galaxies in the Local group o Our local group is located in the outskirts of the local supercluster Illustration of the UniverseEarthSolar System GalaxyLocal GroupLocal Supercluster The Big Bang and the Expanding UniverseAverage distance between galaxies are increasing but individual galaxies and planets and stars occupy regions where gravity has won out against the overall expansion and do NOT expandPoint where expansion began The Big Bang14 billion years ago estimated by rate of expansion Our Cosmic Origins Starslives when it shines with energy from fusion and dies when it exhausts its usable fuelborn when gravity compresses clouds of gas and dust to the point where the center becomes dense and hot enough to generate energy by nuclear fusion planets may form in surrounding disksmassive stars die in titanic explosions called supernovae Early universecontained only the simplest chemical elements hydrogen and helium and a trace of lithiumwe and Earth are made primarily of other elements such as carbon nitrogen oxygen and ironthese other elements were manufactured by stars some through the nuclear fusion that makes stars shine and others through nuclear reactions accompanying the explosions that end stellar livesby the time our solar system formed about 4billion years ago earlier generations of stars had converted about 2 of our galaxys original hydrogen and helium into heavier elements2 may sound small but it made the small rocky planets of our solar system including Earth Basic Astronomical Objects Units and Motions Basic Astronomical Objects Star a large glowing ball of gas that generates heat and light through nuclear fusion in its corePlanet a moderately large object that orbits a star and shines primarily by reflecting light from its starAn object can be considered a planet only if it 1 orbits a star 2 is large enough for its own gravity to make it round 3 has cleared most other objects from its orbital path Dwarf planet object that meets the first two criteria but has not cleared its orbital path ie Pluto Moon or satellite an object that orbits a planet Satellite can refer to any object orbiting another object Asteroid a relatively small and icerich 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 Collections of Astronomical objects Solar system the Sun and all the material that orbits it including planets dwarf planets and small solar system bodiesStar system a star sometimes more than one star and any planets and other materials that orbit it Galaxy a great island of stars in space containing from a few hundred million to over a trillion stars all held together by gravity and orbiting a common center Billions are scattered throughout space some are fairly isolated but many are found in groups Galaxy clusters or groups a collection of galaxies bound together by gravity Small collections up to a few dozen galaxies are generally called groups while larger collections are called clusters They are arranged in giant chains and sheets with huge voids between them Supercluster a gigantic region of space where many individual galaxies and many groups and clusters of galaxies are packed more closely together than anywhere else in the universe Universe or cosmos the sum total of all matter and energythat is all galaxies and everything between them Observable universe the portion of the entire universe that can be seen from Earth The observable universe is probably only a tiny portion of the entire universe
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