Digital Universe Guide - Hayden Planetarium

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176 4. THE EXTRAGALACTIC ATLAS 4.3.8 Local Galaxies Group Name local Reference Revision on the Nearby Galaxies Catalogue, Cambridge University Press (Tully, 1988; revised 2003) Prepared by R. Brent Tully (U Hawaii) Stuart Levy (NCSA/U Illinois) Labels Yes Files g8local.speck, g8local.label Dependencies none Census 247 galaxies The galaxies in the local data group represent the best picture we have of the galactic neighborhood. These 247 objects compose a collection of galaxies that is more complete than other galaxy surveys, which typically show only larger and brighter galaxies. These galaxies were compiled by Brent Tully at the University of Hawaii. Known for discovering the Tully-Fisher relation, a correlation between the luminosity and the rotation period of a spiral galaxy, Brent dedicates his time toward understanding the structure of the <strong>Universe</strong>. Data Variables The nearby galaxies have data variables that describe their brightness, size, and orientation. We list these variables in the following table. Data Variables for the Local Galaxies Number Name Description Units 0 type Galaxy Morphological Type — 1 diamkpc Galaxy diameter kpc 2 Mblueneg Negative absolute B magnitude mag 3 lum Galaxy luminosity scaled to Mblueneg — 4 txno Texture number — 5 cloud The cloud (grouping) number — 6 pgc Principal Galaxies Catalogue number — 7 hicnt References for a grouping catalog — 8–13 orient0 Unit vectors for the polygon orientation Mpc The galaxy morphological type variable is an integer that reflects the type of galaxy classified first by Edwin Hubble (1889–1953) in the 1930s. The classification scheme has four main groups: elliptical galaxies (E), barred spiral galaxies (SB), unbarred spiral galaxies (S), and irregular galaxies (Irr). The integers assigned to these types are decoded in the table below. In this numbering system, barred and
4.3. EXTRAGALACTIC DATA GROUPS 177 unbarred spiral galaxies (S & SB) are merged, since data on bars are often inconclusive. For an overview of galaxy classification, see “Galaxies” in the extragalactic overview. Galaxy Morphology Codes and Census Number Hubble Type Galaxy Type Census -5 E Elliptical 20 -3 E/SO Elliptical/Lenticular 1 3 -2 SO Lenticular 2 0 SO/a Lenticular/Spiral 39 1 Sa Spiral 0 2 Sab Spiral 3 3 Sb Spiral 3 4 Sbc Spiral 1 5 Sc Spiral 8 6 Scd Spiral 9 7 Sd Spiral 12 8 Sdm Spiral 12 9 Sm Spiral/irregular 15 10 Irr Irregular 117 12 S Spiral/irregular 2 0 13 P Peculiar 0 This table also describes the population of galaxies in the data set. Most of them are irregular galaxies, with SO/a spirals (mostly dwarfs) are the second-highest population in the data set. Most of the galaxies around us are small, but is this true elsewhere in the <strong>Universe</strong>? Turns out the answer is probably yes, and we happen to live in a large galaxy. Other data variables describe the galaxy’s size, brightness, and orientation. diamkpc is the diameter of the galaxy in kiloparsecs (the Milky Way is 100,000 light-years in diameter, which equals 30 kpc). Mblueneg is the negative value of the intrinsic B magnitude of the galaxy. The luminosity is a linear scaling of the intrinsic B magnitude, with lum = 1 corresponding to Mblueneg = 19. In this data set, a galaxy is often a member of a group, a cluster, a cloud, and a supercluster. Many groups and clusters of galaxies form a cloud, and many clouds form a supercluster. For example, the Milky Way belongs to the Local Group, which is in the Virgo Supercluster, which is part of the Pisces-Cetus Supercluster Complex. The pgc variable is the Principal Galaxies Catalogue number, and the hicnt is a cross-referencing 1 classification uncertain
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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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3.3. 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 101 3.3.
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Page 145 and 146: 4 The Extragalactic Atlas The word
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Page 211 and 212: absolute magnitude M, can be calcul
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Page 215 and 216: Appendix D Electromagnetic Spectrum
Page 217 and 218: Appendix E Constants and Units In a
Page 219 and 220: Metric Prefixes These prefixes are
Page 221 and 222: INDEX 221 center command, 50, 61 cl
Page 223 and 224: INDEX 223 Earth’s radio signals,
Page 225 and 226: 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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