Digital Universe Guide - Hayden Planetarium

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30 3. THE MILKY WAY ATLAS Slider (choose alpha from the Slider Menu) to increase or decrease the opaqueness. If alpha = 0, the lines are completely transparent (invisible); if alpha = 1, the lines are opaque. We don’t recommend using an alpha of 1, as it will produce unwanted graphics effects. Use alpha = 0.99 if you want really bright lines. You may also use the Partiview Command Line to set an alpha value. For example, type alpha 0.5 to bring the lines to half transparency. Changing Their Color If you’re unhappy with the colors we’ve chosen, you are free to change it. In Partiview, particles are assigned a color set by the color command; however, objects and labels are assigned color using the cment and textcment commands. Well, it’s actually more complicated than that. cment assigns a red-green-blue color to a reference number called a color index, and this color index is then assigned to the object. In the <strong>Digital</strong> <strong>Universe</strong>, we try to use color indexes of 1 when possible. Occasionally, a data group has more than one object or more than one color assigned to an object (as is the case for the constellations), making it necessary to use more than one color index. For the constellations, we use a color index of 3 for Orion and Ursa Major, a color index of 2 for the zodiacal constellations, and a color index of 1 for the remaining constellations. Partiview will report the color assigned to color index 1 when you type cment 1 and so on, replacing “1” for the remaining color indexes. Remember, the colors are expressed in red, green, blue values, which range from 0–1. A color value of 0 means there is no color present, while a value of 1 is color saturation. For a pure red color we have (R, G, B) = (1, 0, 0). White is (R, G, B) = (1, 1, 1), black is (R, G, B) = (0, 0, 0), and pure yellow is (R, G, B) = (1, 1, 0). To make the lines a nice greenish color, type cment 1 .2 .7 .2. Changing the Label Color Similarly, the label color may be changed with the textcment command: textcment 1 .2 .7 .2
3.2. MILKY WAY ATLAS TUTORIAL 31 You may notice that the labels appear much brighter than the lines. This is because the lines have an alpha channel factored into their display. Bring the alpha up to 0.9 and the lines and labels will resemble one another. This is not the best solution, though, as the lines dominate the view. Better to bring the alpha down so that the lines are subtle, then desaturate the label color. For example, the commands alpha 0.4 textcment 1 0.05 0.4 0.05 will bring the color of the lines and labels into general agreement. If you like these changes and wish to preserve them, open the mw.cf file and change the values for these commands in the constellation section. Tutorial: Coordinates in the Sky Goals: Familiarize yourself with the different coordinate systems; discover what these systems tell us about the Galaxy and our position in it. Before starting, turn on: stars, mwVis You will be using: radec, eclip, galac, altLbl, cment and fov commands Coordinate systems are used primarily to locate objects in the sky. There are several Earth-based systems that astronomers use to describe the position of an object. One is based on Earth’s system of longitude and latitude, while another is based on the plane of the Solar System. Yet another is based on the plane of our Galaxy. Equatorial Coordinates Resemble Earth’s Coordinates in the Sky With the Milky Way Atlas running and from the home position, turn on the radec group. These are the equatorial coordinates. This system is based on Earth’s longitude and latitude; the brighter blue line is the celestial equator, the line projected on the sky from our equator on Earth. Pan around and you will see the north and south celestial poles, those points directly above the North and South poles on Earth. In the sky, the equivalent to Earth’s latitude is called declination (Dec) and is measured from +90 ◦ at the north celestial pole to −90 ◦ at the south celestial pole. Longitude is called right ascension (RA) and is measured from 0 to 24 hours. You can find more information on this system in “Equatorial Coordinates Sphere.” The coordinates are labeled in 10-degree increments for declination and every hour for right ascension.
Page 1 and 2: The Digital Universe Guide Brian Ab
Page 3 and 4: Contents Contents 3 List of Tables
Page 5 and 6: List of Tables 2.1 Log and Linear F
Page 7 and 8: 1.2. GETTING HELP 7 1.2 Getting Hel
Page 9 and 10: 1.5. ACKNOWLEDGMENTS 9 1.5 Acknowle
Page 11 and 12: 2.2. LAUNCHING THE MILKY WAY ATLAS
Page 13 and 14: 2.3. LEARNING TO FLY PARTIVIEW 13 T
Page 15 and 16: 2.3. LEARNING TO FLY PARTIVIEW 15 M
Page 17 and 18: 2.4. PARTIVIEW’S USER INTERFACE 1
Page 23 and 24: 2.5. DIGITAL UNIVERSE FILES 23 File
Page 25 and 26: 3.1. MILKY WAY ATLAS OVERVIEW 25 3.
Page 27 and 28: 3.2. MILKY WAY ATLAS TUTORIAL 27 3.
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Page 47 and 48: 3.2. MILKY WAY ATLAS TUTORIAL 47 No
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Page 67 and 68: 3.3. MILKY WAY DATA GROUPS 67 Earth
Page 69 and 70: 3.3. MILKY WAY DATA GROUPS 69 Data
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Page 73 and 74: 3.3. MILKY WAY DATA GROUPS 73 3.3.3
Page 75 and 76: 3.3. MILKY WAY DATA GROUPS 75 3.3.4
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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 91 3.3.1
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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 99 3.3.1
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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 107 righ
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3.3. MILKY WAY DATA GROUPS 109 beyo
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3.3. MILKY WAY DATA GROUPS 121 Othe
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3.3. MILKY WAY DATA GROUPS 123 abou
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3.3. MILKY WAY DATA GROUPS 125 Obje
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3.3. MILKY WAY DATA GROUPS 141 this
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3.3. MILKY WAY DATA GROUPS 143 Not
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4 The Extragalactic Atlas The word
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4.1. EXTRAGALACTIC ATLAS OVERVIEW 1
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4.2. EXTRAGALACTIC ATLAS TUTORIAL 1
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4.3. EXTRAGALACTIC DATA GROUPS 169
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4.4. OPTIMIZING THE EXTRAGALACTIC A
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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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Digital Universe Guide - Hayden Planetarium

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