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Galaxy_Analysis_lab_03-30-10-1 - Galactic Astronomy with...

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Galactic Astronomy with Citizen Scientists Learning Goals: Students will participate in an online volunteer effort to contribute to galactic astronomy called Galaxy Zoo. They will learn how volunteers, or citizen scientists, can be part of a solution for analyzing large astronomy datasets such as the Sloan Digital Sky Survey. Materials: Galaxy Zoo website and Galaxy Mergers on Galaxy Zoo site Pre-lab activity: Galactic Astronomy with Citizen Scientists pre-lab exercise Introduction: Galaxies are large structures containing a combination of stars, interstellar gas and dust, and dark matter. A single galaxy can have as few as a million (10 6 ) stars for a dwarf galaxy to as many as a trillion (10 12 ) stars for a giant elliptical galaxy. These stars, and the other forms of matter, are all gravitationally bound to the galaxy making it, in one sense, a single structure. The diameter of galaxies ranges from about 1,000 to 100,000 parsecs. The number of galaxies in the visible universe is estimated to be on the order of hundreds of billions (10 11 ). Galaxies are important for many reasons. They form the building blocks for the large-scale structure of the universe. By observing galaxies, astronomers can test theories about how the universe began and how it might evolve in the future. Traditionally, astronomers have categorized, or classified, galaxies according to their shape. This type of scheme is also referred to as morphological. The most widely used is the Hubble Classification Scheme. (see figure below) Hubble Scheme image from NASA - MSU/Bozeman CERES Project In this scheme, various types of elliptical galaxies are on the left. Their shapes change from round spherical types, through more squashed watermelon-like shapes, to a stretched, or prolate, cigar-like shape. These designations all begin with E. In the middle of the diagram is a class of galaxies known as lenticulars and are given the designator S0. These galaxies have a large central bulge that is similar to elliptical galaxies. However,
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they also have a flat disk-like region, which, though it apparently lacks spiral arms, is similar to spiral galaxies. Branching away from the S0 galaxies are the spiral galaxies. The top branch contains spiral galaxies arranged according to the size of their central bulge and the tightness of the spiral arms. These are labeled Sa, Sb, and Sc. The bottom branch contains spiral galaxies that have bars connecting the bulge to the spiral arms. The galaxies are labeled SBa, SBb, and SBc. This scheme as originally proposed by Edwin Hubble in the 1930s classified any other galaxy that did not fit into one of the previous types as simply “irregular”. Other schemes, such as one proposed by de Vaucouleurs, have extended the original one by adding additional spiral categories, a third “fork”, and categorizing dwarf galaxies.
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