Digital Universe Guide - Hayden Planetarium

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160 4. THE EXTRAGALACTIC ATLAS mark from where we came. You should see the large labels delineating the Virgo Cluster, Fornax Cluster, and you may possibly see the Centaurus and Hydra Clusters too. These are the nearest galaxy clusters to Earth. Continue moving away from the Milky Way to see the entire data set, then adjust the brightness so the structure of the Universe pops out—the red clusters, orange and yellow filaments, out to the faint blue galaxies. From this vantage point, let’s orbit around the Milky Way. (You will need to adjust the brightness of these data using the Slum Slider throughout this tutorial.) Seeing the Forest Through the Trees First, let’s see the entire 2MASS data set so we know what this picture really looks like without filtering. Type see all and all 1,140,931 galaxies are displayed. Here you have a sense of just how dense the Universe is. And, 2MASS only observed relatively bright galaxies. With this view, we no longer see the structure of the Universe so easily. To return to our filtered view showing the large-scale structure, type see lss The Proximity Factor The lss selection is set using a data variable called the proximity factor. The 2MASS data come with two proximity factors, one for R = 2 Mpc and one for R = 5 Mpc (Mpc means megaparsecs with 1 Mpc = 1,000,000 pc and 1 pc = 3.26 light-years). These factors describe the density of space around a particular galaxy. Specifically, the R = 2 Mpc and R = 5 Mpc factors, called prox2 and prox5, respectively, are high when there are many galaxies within the specified radius, and they are low when a galaxy is by itself in space. The sheer number and density of galaxies in 2MASS demands that we use creative ways to view these data. By default, we use the lss selection set in the extragalactic.cf file with the command only= prox5 > 0.7. This command tells Partiview to display only those galaxies with prox5 > 0.7, resulting in only 15% of total number shown. Removing 85% of the data may not seem logical, but allows us to see structure. Dense Clusters We have also defined a selection expression to display the dense clusters. Type the command
4.2. EXTRAGALACTIC ATLAS TUTORIAL 161 see clusters and you will see the most dense regions of the nearby Universe. This selection is defined using the prox2 proximity factor in the command thresh prox2 1.3 3. Increase the label size to see the names of these clusters. Type see lss to return to the normal view. Color Schemes Type color and Partiview will report that colors are mapped to these galaxies using the prox5 data variable. We have defined a color map file and several color schemes to highlight various aspects of these data. First, and most obvious, we can view the galaxies at a constant color. Type color const and the galaxies will change to an aqua color. Sometimes, a constant color is good for seeing structure and puts all the galaxies on common ground. Of course, you can change this constant color to any red-green-blue values you like, for example, make the points gray by typing or color const .5 .5 .5 The galaxies may also be colored by distance using either color distMly color redshift These set the innermost galaxies to aqua, then continues to green, yellow, orange, and red for the farthest galaxies. Coloring by proximity is the best way to highlight structure in the data set. The default color for the data group is color prox5 which, as mentioned above, sets the color of each point based on the R = 5 Mpc proximity factor. We have also defined a similar color map for the prox2 proximity factor
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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 29 Wi
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3.2. MILKY WAY ATLAS TUTORIAL 31 Yo
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3.2. MILKY WAY ATLAS TUTORIAL 41 li
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3.2. MILKY WAY ATLAS TUTORIAL 45 In
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3.2. MILKY WAY ATLAS TUTORIAL 47 No
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3.2. MILKY WAY ATLAS TUTORIAL 49 Th
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3.2. MILKY WAY ATLAS TUTORIAL 51 to
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3.2. MILKY WAY ATLAS TUTORIAL 55 th
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3.2. MILKY WAY ATLAS TUTORIAL 57 bi
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3.2. MILKY WAY ATLAS TUTORIAL 59 in
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3.2. MILKY WAY ATLAS TUTORIAL 63 mo
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3.2. MILKY WAY ATLAS TUTORIAL 65 fa
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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 71 The l
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3.3. MILKY WAY DATA GROUPS 73 3.3.3
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3.3. MILKY WAY DATA GROUPS 77 If yo
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3.3. MILKY WAY DATA GROUPS 79 lumin
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3.3. MILKY WAY DATA GROUPS 81 not p
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3.3. MILKY WAY DATA GROUPS 83 Two p
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3.3. MILKY WAY DATA GROUPS 85 expre
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3.3. MILKY WAY DATA GROUPS 87 marke
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3.3. MILKY WAY DATA GROUPS 89 brigh
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3.3. MILKY WAY DATA GROUPS 93 inclu
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3.3. MILKY WAY DATA GROUPS 95 old.
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3.3. MILKY WAY DATA GROUPS 97 centi
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3.3. MILKY WAY DATA GROUPS 101 3.3.
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3.3. MILKY WAY DATA GROUPS 103 heat
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3.3. MILKY WAY DATA GROUPS 105 3.3.
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3.3. MILKY WAY DATA GROUPS 107 righ
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Page 145 and 146: 4 The Extragalactic Atlas The word
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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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Digital Universe Guide - Hayden Planetarium

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