Digital Universe Guide - Hayden Planetarium

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164 4. THE EXTRAGALACTIC ATLAS Bring back all the Abell clusters by typing see all. The gray points, which are the majority of points, are not connected to any major supercluster, but remain as a nexus between the filaments and galaxies that must be present, but remain invisible in these data sets. Next, we explore two partial galaxy surveys, the Two Degree Field Survey and the Sloan Digital Sky Survey. 4.2.7 Tutorial: Galaxy Surveys Goals: Understand the extragalactic data from Earth’s perspective; begin exploring the 2dF and Sloan galaxies. Before starting, turn on: galaxy, stars, constel, mwVis, galac You will be using: 2dFgals, SloanGals, 1Gly, 20Gly If you’re continuing from a previous tutorial, quit Partiview and restart the Extragalactic Atlas for a fresh start. Once the Atlas appears, turn off the local group. You should be left with the Point of Interest marker. Fly toward it until it disappears. Now you should see nothing. We’re first going to look at these surveys from Earth. Turn on the stars, constel, mwVis, and the galac groups so that you see the stars, constellations, visible all-sky image, and the constellations for reference. Viewing Galaxy Surveys from Earth Turn on the 2dF Galaxy Redshift Survey (2dFgals). As you pan around the sky, you will see one strip of yellow toward the northern Galactic latitudes and another strip surrounded by circular patches in the south Galactic polar region. Each of these patches of galaxies shows the actual telescope footprint on the sky. If you look at each closely, you will see they are two degrees wide and contain many galaxies. Now turn on the SloanGals group to see the Sloan Digital Sky Survey galaxies. You will see more coverage on the sky, particularly in the northern Galactic hemisphere. These are two major galaxy surveys that astronomers have completed. As you can see, they cover only a portion of the entire sky, often in narrow strips. Now turn off the Sloan galaxies so that you’re left with only the 2dF survey. Position yourself so you’re looking toward the random fields (circular patches) in the south Galactic pole. Begin flying away and, as you do, notice the random fields appear to be pulled in toward the Milky Way. You may also
4.2. EXTRAGALACTIC ATLAS TUTORIAL 165 notice that the stars, Milky Way all-sky, constellations, and coordinates all lie on a fixed sphere. Because the distance to the stars would be extremely small on this scale (megaparsecs), we placed the stars and related data groups on a fixed sphere with a radius of 1 Mpc (1 million parsecs). Flying Away from Earth As you pull back, you’ll be out of the data set in no time. Once you see most of the galaxies, stop and orbit. From out here, you can see the large-scale structure of the Universe: dense clusters of galaxies connected by strands of galaxies, and areas where there are fewer galaxies, called voids. Turn on the 1-billion-light-year grid, 1Gly, and the 20-billion-light-year grid, 20Gly, to see the scale of these galaxies. The random pointings now appear as pencil beams that extend out billions of light-years from the Milky Way. The bow-tie shape of these data indicates the patches of sky that were surveyed. Imagine if the entire sky were surveyed, you would see similar data surrounding the Milky Way in a spherical distribution. The Sloan Digital Sky Survey’s original goals were to do just that. Let’s turn the SloanGals back on and see them in 3-D. You may want to adjust their brightness using the Slum Slider. The Sloan galaxies also show the large-scale structure, that pattern of clusters, filaments, and voids. This is the structure of the local Universe. Remember, for a galaxy 3 billion light-years away, the light traveled for about 3 billion years to reach the lens of the observing telescope. Does the evolution of the Universe affect this view? How far do you have to look before the large-scale structure you see currently is nonexistent or is in an unrecognizable phase? We will continue exploring these questions in subsequent tutorials. For this scale, we are still looking at objects generally in the same cosmic era. Yes, when we look at a galaxy 3 billion light-years away, we’re seeing it as it was 3 billion years ago. However, this is a relatively short time, cosmically. Next we’ll discuss quasars, objects that we see at greater distances. 4.2.8 Tutorial: Quasar Surveys Goals: Explore the characteristics of the quasar surveys. Before starting, turn on: 2dFgals You will be using: 2dFQSOs, SloanQSOs, 20Gly, alpha 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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3.3. 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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Page 145 and 146: 4 The Extragalactic Atlas The word
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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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Digital Universe Guide - Hayden Planetarium

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