1To Do TodayFinish up the worksheet from last time: 15 minutesClass prep & discussionOverview: Galaxies and DistancesWriting Exercise: Strength on the Sentence Level5 Minutes: Prep for Class Discussion How do you feel about the idea in the reading that the Big Bang model can do nothing to say what caused or came before the Big Bang? The diagram at right shows the different forms of energy in the Universe. What do you think about this information? Are you surprised? What was one topic in this reading that you would like to know more about (including specific questions)?2Class DiscussionHow do you feel about the idea in the reading that the Big Bang model can do nothing to say what caused or came before the Big Bang?Class DiscussionThe diagram shows the different forms of energy in the Universe. What do you think about this information? Are you surprised?3Class DiscussionWhat was one topic in this reading that you would like to know more about (including specific questions)?What is a Galaxy?The Wikipedia Definition: “A galaxy is a massive, gravitationally bound system consisting of stars, an interstellar medium of gas and dust, and dark matter.”M31, from Hubble4Spiral GalaxiesAndromeda Galaxy or M31.Our nearest large neighbor“Grand Design” Spirals5“Grand Design” SpiralsThe Whirlpool Galaxy (M51) and an interacting neighborBarred Spiral GalaxiesBarred Spiral Galaxy NGC 1300.The Milky Way is also barred6Elliptical GalaxiesM87 in the Virgo Cluster.Ellipticals look like smooth, featureless “blobs” and show no ordered rotation.How Galaxies Form It turns out dark matter is so much more prevalent than “regular” matter, that the gravity of dark matter has a bigger influence on the development of the Universe than the “normal stuff” does.7How far away are galaxies?Astronomers measure distances in light years. Does anyone know what a light year is?How far away are galaxies?Astronomers measure distances in light years. A light year is the distance that a beam of light can travel in a year.Since light moves at 670 MILLION miles per hour, this is a very long distanceThat’s 186,000 miles per second, so in everyday life you never notice that light has a speed.8…It takes light ___seconds to go from the Earth to the Moon: 238,000 miles1.3 …It takes light ___ minutes to travel from the Sun to the Earth, 93 million miles away8.39It takes light _____ years to travel from our Sun to the nearest star Proxima Centauri, 2.5 x 1013miles awayIf the Sun were scaled down to the size of a period on a printed page, then Alpha Centauri would be around 8 miles away.4.25It takes light _______ years to travel from the center of our own galaxy to the Earth, 1.5 x 1017miles25,50010It takes light ____________ years to travel from Earth to the Andromeda Galaxy, located on the other side of our Local Group of galaxies, 1.7 x 1019miles away2.89 millionIt takes light _________ years to reach the Virgo cluster of Galaxies, which is the most massive portion of the Supercluster our Local Group belongs to, 3.5 x 1020miles away60 million11So galaxies are MILLIONS or BILLIONS of light years away!These numbers are big and clumsy to work with, so usually we use a different system . . .What is a parsec?A parsec is about 3 light years.1 kiloparsec is ______ parsecs12What is a parsec?A parsec is about 3 light years.1 kiloparsec is 1000 parsecsA megaparsec is 1 million parsecs (mega stands for million)A gigaparsec is 1 billion parsecs (gigastands for billion)Why parsecs?Parsecs are a handy length scale:A galaxy can be measured in kiloparsecs(kpc)The Milky Way is about 20 kpc across, and we’re about 10 kpc from the centerDistances between galaxies can be measured in megaparsecs (Mpc)The scale of the whole Universe is measured in gigaparsecs (Gpc)13Distribution of GalaxiesStructures in the Universe: The best place to find a galaxy is next to another one!GroupsClustersSuperclustersFilaments and VoidsDistribution of GalaxiesStructures in the Universe: The best place to find a galaxy is next to another one!GroupsClustersSuperclustersFilaments and VoidsThe local group includes two dominant spiral galaxies, the Milky Way & Andromeda, and about 30 dwarf galaxies14Distribution of GalaxiesStructures in the Universe: The best place to find a galaxy is next to another one!GroupsClustersSuperclustersFilaments and VoidsThe Virgo Cluster is the closest nearby cluster, at about 17 Mpc. It contains about 1500 member galaxies!Distribution of GalaxiesStructures in the Universe: The best place to find a galaxy is next to another one!GroupsClustersSuperclustersFilaments and VoidsSuperclusters are “clusters of clusters” and can extend for hundreds of millions of light years.15Distribution of GalaxiesStructures in the Universe: The best place to find a galaxy is next to another one!GroupsClustersSuperclustersFilaments and VoidsThis simulation contains more than 10 billion particles, and attempts to trace galaxy, cluster & superclusterformation.Essay 1 . . . We’ve still got one more thing to do today!16Essay 1 . . . Find your “starred” sentence and write it down (including any errors you notice!)With your partner, discuss what would make the sentence stronger.Variation? Clauses? Rearrangement?Word choice? Precision? Easy to understand?Work together to rewrite both of your sentences.Check out the “Writing Style” section of Easy Writer for tipsReading AssignmentHooper, Chapter 2Ferreira, Chapter 3Check out the reading questions online!Please BRING these 2 books with you to class next week17Essay 1 Exercise: Be concise!Find your longest sentence and write it on a piece of paperWe’ll pass the papers around the room and shorten each sentence that comes our way by ONE WORD.Tip for conciseness from Easy Writer:Eliminate redundant wordsEliminate “empty” wordsReplace wordy phrasesSimplify sentence structureTry using the active
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