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AS09_Galaxies.docx - Old Dominion University Physics 104N,...

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Old Dominion University Physics 104N, At Home Lab1GalaxiesExperiment AS09NameLab SectionObjectivePart A: Classifying GalaxiesPart B: The Hubble Deep Field: Counting GalaxiesPart C: Measuring the Mass of the Milky Way: Arguing for Dark MatterMaterialsComputer with internet accessHubble Deep Field ImagesCalculatorProcedurePart A: Classifying GalaxiesGalaxy morphological classificationis a system used byastronomersto dividegalaxiesinto groupsbased on their visual appearance.One of the more widely used systems, the Hubble sequence, is amorphological classification scheme for galaxies invented by Edwin Hubble in 1936. It is oftenknown colloquially as the “Hubble tuning-fork” because of the shape in which it is traditionallyrepresented. Hubble’s scheme divides galaxies into three broad classes based on their visualappearance:Elliptical galaxieshave smooth, featureless lightdistributions and appear as ellipses in images. They aredenotedbytheletterE,followedbyanintegerηrepresenting their degree of ellipticity on thesky.Spiralgalaxiesconsistofa flatteneddisk,with stars forminga(usuallytwo-armed) spiral structure, and a central concentration ofstars known as the bulge, which is similar in appearanceto an elliptical galaxy. They are given the symbol "S".Roughly half of all spirals are also observed to have a bar-like structure, extending from the central bulge.These barred spirals are given the symbol "S.B.".Lenticular galaxies(designated S0) also consist of a bright central bulge surrounded by anextended, disk-like structure but, unlike spiral galaxies, the disks of lenticular galaxies have novisible spiral structure and are not actively forming stars in any significant quantity.Don’t be overly concerned if you have not previously considered the many shapes which a galaxycan take; we will learn about them in this laboratory exercise. We will study the appearances ofgalaxy images and spectra, and consider how best to describe and to quantify (define withnumbers) key properties that shed light on the evolutionary state of galaxies.
2Experiment AS09:GalaxiesThe primary goal of this lab is to realize that the Universe is made up of billions of galaxies, somewith properties quite similar to those of our own Milky Way galaxy and some which are quitedifferent. We will explore galaxy luminosities, colors, sizes, and morphologies, and realize that theevolution over the last fourteen billion years of the stars and gas which make up these galaxies, andinteractions between galaxies, have created these variations in1.Visit this website:2.Your first activity is to inspect a small set of galaxies, and to group them according to thefeatures which seem most important to you. There are no “wrong answers” in this process, sotake your time, carefully observe shapes, color variations, and subtle differences between thegalaxies, and have fun.

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