Digital Universe Guide - Hayden Planetarium

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82 3. THE MILKY WAY ATLAS 3.3.7 Extrasolar Planets Group Name expl Reference The Extrasolar Planets Encyclopaedia Jean Schneider (CNRS/LUTH, Paris Observatory) Prepared by Brian Abbott (AMNH/<strong>Hayden</strong>) Labels Yes Files expl.speck, expl.label Dependencies target-blue.sgi Census 725 planets in 520 systems Extrasolar planets, or exoplanets, are a relatively new phenomenon in astronomy. While many astronomers believed in their existence, no observational evidence was available until 1995. Since that time, we have discovered 520 systems consisting of one or more planets around a host star. These planets were not discovered in the traditional sense of past planetary discoveries; they are so far away and so small that we cannot actually see them. Instead, for many of the systems, the host star’s spectrum is analyzed, and an extremely small motion is inferred for the star. This tiny motion is due to the orbiting planet. While we think of the Sun as being stationary, it actually moves, or wobbles, because of the planets that orbit around it. The larger the planet, the larger the wobble. This is because the center of the orbit is actually located at a point called the “center of mass” of the system. So, for example, the Sun-Jupiter system’s center of mass is more than 778,000 kilometers (483,000 miles) from the Sun’s center. This point, along the line connecting the two bodies, lies just outside the Sun’s photosphere, or “surface,” which has a radius of about 696,000 km (432,000 miles). While we do not perceive it, the Sun is orbiting this point and would be observed to wobble from a point of view outside the Solar System. Many of the exoplanets were discovered with this observational technique. Other techniques include pulsar timings, measuring the periodic variation in the light arrival time; transit photometry, which measures the periodic variation in the light of the host star; and gravitational microlensing. Planetary Hosts Most planetary systems are hosted by main-sequence stars. These systems take the names of their host star. Some of these stars have Greek names, like Upsilon Andromedae, some have Flamsteed names, like 51 Pegasi, the first system detected in 1995, and others have HD numbers from the Henry Draper star catalog. Each have the lowercase lettered name of the planet or planets in the system. The first planet is named “b,” and subsequent planets are given letters in sequence.
3.3. MILKY WAY DATA GROUPS 83 Two pulsars have been found to host planets and are labeled with “PSR.” The detection method used for pulsars allows their planets to be found at greater distances. The two systems in the atlas are 978 and 12,388 light-years from Earth. Compare that with the main-sequence-star hosts that are within 350 light-years (most are within 150 light-years). The remaining handful were found by microlensing and transit surveys. These are considerably farther, ranging from 500 to 20,000 light-years from Earth. The systems are represented by a blue target around each host star. This image is not meant to represent the orbit of the planet, it is simply a marker. The extrasolar planets have a number of data variables to offer flexibility when visualizing these data. Data Variables for the Extrasolar Planets Number Name Description Units 0 numplanets Number of planets in the system — 1 discovered Year of discovery of the first planet in the system years 2 distly Distance to the system light-years 3 texnum Texture number — You can use these variables in conjunction with the thresh command to see how many systems have more than one planet (thresh numplanets > 2), or how many planets were discovered between 1995 and 2000 (thresh discovered 1995 2000).
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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 133 3.3.
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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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4.4. 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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