Digital Universe Guide - Hayden Planetarium

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50 3. THE MILKY WAY ATLAS the Point of Interest to examine the cluster more effectively. With the cluster in front of you, turn on the alternate star names (altLbl button) and find the star θ 2 Tauri (marked as The2 Tau). You may need to switch into Translate Flight Mode to get the proper perspective. Changing the Point of Interest Location Once you have located the star, bring it close and place the mouse pointer over it. Next press the Shift + p keys (or use Shift + middle mouse button for a three-button mouse). This places the Point of Interest on this star. To confirm that the Point of Interest has moved, increase the size of the Point of Interest marker by using the Censize Slider. The censize command sets the size of the Point of Interest marker in the units of the data you are viewing, which in the case of the Milky Way Atlas is parsecs. You can move it with the slider or enter a value at the command line. Make it exactly 1 light-year by entering censize 0.307 (0.307 parsecs = 1 light-year). Now you have a measuring stick and an idea of the size and scale of the star cluster. With the Point of Interest centered in your view, switch back to Orbit Flight Mode and orbit the cluster with the left mouse button. Turn off altLbl to see the stars without their labels. Also turn on the 10-light-year grid (10ly) to give yourself a reference to the location of the Sun and Solar System. Seeing Uncertainty While you orbit the Hyades star cluster, turn on the stellar distance uncertainty (err). You will see a series of red points, some with blue labels, come on around the star Ain. This is Ain’s distance uncertainty. Notice how these points line up when you look toward the Sun. Astronomers know a star’s position in the sky to great certainty. It’s the distance that is difficult to obtain because of the margin of error associated with it from the parallax measurement. The star is placed at the parallax-derived distance of 154.94 light-years. However, the star could lie anywhere along the red line from 149 to 161 light-years. The red points are spaced in 1-light-year increments with the absence of a point corresponding to the published parallax distance. Bring the Point of Interest back to the Sun. Rather than travel back to the Sun, place the mouse over it, and use the Shift + p to move the Point of Interest, it’s easier to use the Command Line. The center (or interest) command sets where the Point of Interest is. Type the command center 0 0 0
3.2. MILKY WAY ATLAS TUTORIAL 51 to move the Point of Interest back to the Sun so that you return to orbiting the Sun. Pull away from the Hyades and pass near the Pleiades star cluster, with its bright stars and longer uncertainty marker (remember to turn on the open clusters if you have trouble finding the Pleiades). We highlight the distance uncertainty of Pleione, the first star in the handle of the dipper-like asterism. You will immediately notice the uncertainty has grown a lot from that in the Hyades. This increased uncertainty, about eight times greater, affects the overall shape of the star cluster. You may recall that the Hyades was a nice spherical cluster, what you might expect a star cluster to look like. The Pleiades, on the other hand, is slightly stretched along the line of sight to the Sun, parallel to the distance uncertainty. Astronomers call this radial stretching a “finger of god.” Of course, this is an observational artifact—if the telescope were larger, the parallax (and resulting distance) would be more accurate and the cluster would look more spherical. Above the Pleiades is the star Betelgeuse, the bright red giant in Orion’s shoulder (you may have to pull back from the cluster to see it). If you look at its ray of uncertainty, you’ll notice the star is not in the space left for the published trigonometric parallax distance, at 427 light-years. We actually placed the star a bit closer because of the parallax error. For this star, the parallax error was so high that we factored in the photometric distance (the distance derived from knowledge of the star’s brightness and luminosity). With a weighted mean distance between each of these, the star ends up a bit closer. We have chosen a handful of stars for this data group. A list appears in “The Stellar Distance Uncertainty.” Deneb, the bright star in Cygnus, is the farthest star we sample. It is a distant star that is intrinsically very bright. But because it’s far away, the uncertainty ranges from about 2,000 to 7,000 light-years. All Data Have Uncertainties From outside the stellar data group, all these lines of uncertainty point to the Sun and should remind you that all data in the Atlas have uncertainties. From the nebulae and clusters to galaxies outside the Milky Way, each point has an uncertainty that depends on the technique used to determine its distance. Tutorial: Sorting Stars by Color Goals: Contrast the differences in stellar color. Before starting, turn on: stars You will be using: galaxy, see and showbox commands
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.
Page 29 and 30: 3.2. MILKY WAY ATLAS TUTORIAL 29 Wi
Page 31 and 32: 3.2. MILKY WAY ATLAS TUTORIAL 31 Yo
Page 33 and 34: 3.2. MILKY WAY ATLAS TUTORIAL 33 th
Page 35 and 36: 3.2. MILKY WAY ATLAS TUTORIAL 35 Op
Page 39 and 40: 3.2. MILKY WAY ATLAS TUTORIAL 39 co
Page 41 and 42: 3.2. MILKY WAY ATLAS TUTORIAL 41 li
Page 45 and 46: 3.2. MILKY WAY ATLAS TUTORIAL 45 In
Page 47 and 48: 3.2. MILKY WAY ATLAS TUTORIAL 47 No
Page 49: 3.2. MILKY WAY ATLAS TUTORIAL 49 Th
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Page 57 and 58: 3.2. MILKY WAY ATLAS TUTORIAL 57 bi
Page 59 and 60: 3.2. MILKY WAY ATLAS TUTORIAL 59 in
Page 63 and 64: 3.2. MILKY WAY ATLAS TUTORIAL 63 mo
Page 65 and 66: 3.2. MILKY WAY ATLAS TUTORIAL 65 fa
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
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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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