Digital Universe Guide - Hayden Planetarium

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156 4. THE EXTRAGALACTIC ATLAS than dimmer ones. Only 11 galaxies are bright enough to make this cut. They include the Milky Way, Andromeda, M33, M81, and the giant elliptical Centaurus A. Within a galaxy, the luminous stars are few and far between compared with the number of dimmer stars. Galaxies appear to follow this trend, as most of the nearby galaxies have low luminosities. This picture of the nearby galaxies is the best science has to offer. Of course, there are many small, dimmer galaxies that we cannot see, even in our own backyard. Let’s look at other galaxy surveys that map galaxies out to greater distances. 4.2.3 Tutorial: Local Large-Scale Structure Goals: Explore the local structure of the Universe. Before starting, turn on: galaxy, local, Tully You will be using: clipbox, polysize commands In the previous sections, we described the Local Group of galaxies and the groups of galaxies that surround the Local Group. Now you will explore the structure of the local Universe and see what lies beyond the surrounding galaxy groups. Fly out of the local galaxies (local) and turn on the Tully Galaxy Catalog (Tully). Tully’s multicolored points now occupy the rest of your view. Look only at the nearest galaxies by setting a clip box for these data. Run the command clipbox 0,0,0 30,30,30 This shows only the galaxies within 30 megaparsecs, about 100 light-years. Now fly outside of this box so that you have a view of the entire data set. Brighten the galaxies if necessary. The most dominant feature is the dense red cluster near the center. Fly to this galaxy cluster. This dense cluster could be considered “downtown” for our region of the Universe, the center of our local supercluster. This is the Virgo Cluster. The Virgo Cluster Sixteen of Messier’s galaxies are members of the Virgo Cluster, but this is a mere fraction of Virgo’s 2,000-plus galaxies. While it is about 50 million light-years away, the immense gravity of the cluster affects our Local Group galaxies and pulls other galaxies toward it.
4.2. EXTRAGALACTIC ATLAS TUTORIAL 157 Now turn off the points and labels and turn off the local data group. If you fly right into the cluster, you may notice the faint glow of a few bright galaxies. In fact, the Tully Catalog has images placed on each point that represents the type of galaxy it is. These images are given the proper size and orientation, and the luminosity of the points is accurate. If you wish to see these images more prominently, increase their polysize. Because their slum value is fixed according to the galaxy’s size, you will have to use the polysize command to increase the size of the polygons. Choose polysize from the Slider Menu and adjust the slider to your liking. Turn on the labels for the Tully data set. You may see labels like M31, which refer to the Messier Catalog, or NGC 4429, which refer to the New General Catalog. At the center of the Virgo Cluster is M87, a massive elliptical galaxy extending out more than half a million light-years. Its most peculiar feature is the long, knotty jet of material streaming out from its center. Reduce the polysize back to normal (the Polysize Slider should be at its left-most setting) and turn the points back on. If you orbit the Milky Way with the Virgo Cluster in sight, you will notice a stream of light-blue galaxies extending up toward the Virgo Cluster. This is the Ursa Major filament that, in the 2-D sky, traces a path from the constellation Virgo up to Ursa Major. The scientist who compiled these data sets into one consistent catalog, Brent Tully of the Institute for Astronomy in Hawaii, color-coded the galaxies according to a group membership. All galaxies belonging to dense clusters are red, while the galaxies in the Local Group and other nearby groups are green. Galaxies belonging to the Ursa Major Filament are light blue. Many more clusters, filaments, and spurs are out there. Within this 100-light-year box are more than 6,800 galaxies. Let’s look at the entire data set by typing cb off removing the clip box and revealing the remaining 20,000 or so galaxies. We discuss this larger view of the Universe in the next section. 4.2.4 Tutorial: Tully’s Nearby Galaxies Goals: Discuss the structure of the nearby Universe. Before starting, turn on: galaxy, local, Tully You will be using: see command
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The Digital Universe Guide Brian Ab
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Contents Contents 3 List of Tables
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List of Tables 2.1 Log and Linear F
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1.2. GETTING HELP 7 1.2 Getting Hel
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1.5. ACKNOWLEDGMENTS 9 1.5 Acknowle
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2.2. LAUNCHING THE MILKY WAY ATLAS
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2.3. LEARNING TO FLY PARTIVIEW 13 T
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2.3. LEARNING TO FLY PARTIVIEW 15 M
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2.4. PARTIVIEW’S USER INTERFACE 1
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2.5. DIGITAL UNIVERSE FILES 23 File
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3.1. MILKY WAY ATLAS OVERVIEW 25 3.
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3.2. MILKY WAY ATLAS TUTORIAL 27 3.
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3.2. MILKY WAY ATLAS TUTORIAL 51 to
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3.3. MILKY WAY DATA GROUPS 67 Earth
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3.3. MILKY WAY DATA GROUPS 69 Data
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3.3. MILKY WAY DATA GROUPS 73 3.3.3
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3.3. MILKY WAY DATA GROUPS 79 lumin
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3.3. MILKY WAY DATA GROUPS 101 3.3.
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Page 145 and 146: 4 The Extragalactic Atlas The word
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Appendix A Light-Travel Time and Di
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Appendix B Parallax and Distance On
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absolute magnitude M, can be calcul
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discovered that there was a linear
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Appendix D Electromagnetic Spectrum
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Appendix E Constants and Units In a
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Metric Prefixes These prefixes are
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INDEX 221 center command, 50, 61 cl
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INDEX 223 Earth’s radio signals,
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INDEX 225 irregular galaxy, 147, 17
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INDEX 227 entering, 21 every, 206 j
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INDEX 229 stellar distance uncertai
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