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TAMU ASTR 101 - Lecture02

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Copyright © 2009 Pearson Education, Inc.Doing Science“Science is figuring out stuff and not foolingyourself in the process.”Richard FeynmanCopyright © 2009 Pearson Education, Inc.What is our place in the universe?Our “cosmic address”Insert ECP 5e Figure 1.1Copyright © 2009 Pearson Education, Inc.A large, glowing ball of gas that generates heat andlight through nuclear fusionStarCopyright © 2009 Pearson Education, Inc.PlanetA moderately large object that orbits a star; itshines by reflected light. Planets may be rocky,icy, or gaseous in composition.MarsNeptuneCopyright © 2009 Pearson Education, Inc.Moon (or satellite)An object that orbitsa planetGanymede (orbits Jupiter)Copyright © 2009 Pearson Education, Inc.Asteroid A relatively smalland rocky objectthat orbits a starIdaCopyright © 2009 Pearson Education, Inc.Comet A relativelysmall and icyobject thatorbits a starCopyright © 2009 Pearson Education, Inc.Solar (Star) SystemA star and all the material that orbitsit, including its planets and moonsCopyright © 2009 Pearson Education, Inc.Solar (Star) SystemCopyright © 2009 Pearson Education, Inc.NebulaAn interstellar cloudof gas and/or dustCopyright © 2009 Pearson Education, Inc.GalaxyA great island of stars in space, all heldtogether by gravity and orbiting acommon centerM31, the Great Galaxy in AndromedaCopyright © 2009 Pearson Education, Inc.UniverseThe sum total of all matter and energy;that is, everything within and betweenall galaxiesCopyright © 2009 Pearson Education, Inc.How did we come to be?Copyright © 2009 Pearson Education, Inc.How did we come to be?Copyright © 2009 Pearson Education, Inc.How did we come to be?Copyright © 2009 Pearson Education, Inc.How did we come to be?Copyright © 2009 Pearson Education, Inc.How can we know what the universe waslike in the past?• Light travels at a finite speed (300,000 km/s).• Thus, we see objects as they were in the past:The farther away we look in distance,the further back we look in time.2.5 million yearsAndromeda Galaxy8 yearsSirius8 minutesSun1 secondMoonLight travel timeDestinationCopyright © 2009 Pearson Education, Inc.Example:This photo shows the Andromeda Galaxy as it looked about1/2 million years ago.Question: When will we be able to see what it looks like now?M31, the Great Galaxy in AndromedaCopyright © 2009 Pearson Education, Inc.Definition: Light-Year• The distance light can travel in 1 year• About 10 trillion kilometers (6 trillionmiles)Copyright © 2009 Pearson Education, Inc.• At great distances, we see objects as they were when the universe was much younger.Copyright © 2009 Pearson Education, Inc. Can we see the entire universe?Copyright © 2009 Pearson Education, Inc.Thought QuestionA. Because no galaxies exist at such a greatdistance.B. Galaxies may exist at that distance, but theirlight would be too faint for our telescopes to see.C. Because looking 15 billion light-years awaymeans looking to a time before the universeexisted.Why can’t we see a galaxy 15 billion light-yearsaway?(Assume the universe is 14 billion years old.)Copyright © 2009 Pearson Education, Inc.Thought QuestionA. Because no galaxies exist at such a greatdistance.B. Galaxies may exist at that distance, but theirlight would be too faint for our telescopes tosee.C. Because looking 15 billion light-years awaymeans looking to a time before the universeexisted.Why can’t we see a galaxy 15 billion light-yearsaway?(Assume the universe is 14 billion years old.)Copyright © 2009 Pearson Education, Inc.What have we learned?• What is our place in the universe?— Earth is part of the solar system, which is theMilky Way Galaxy, which is a member ofthe Local Group of galaxies in the LocalSupercluster.• How did we come to be?— The matter in our bodies came from the BigBang, which produced hydrogen and helium.— All other elements were constructed from Hand He in stars and then recycled into newstar systems, including our solar system.Copyright © 2009 Pearson Education, Inc.What have we learned?• How can we know what the universe waslike in the past?— When we look to great distances, we areseeing events that happened long agobecause light travels at a finite speed.• Can we see the entire universe?— No. The observable portion of the universe isabout 14 billion light-years in radius becausethe universe is about 14 billion years


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