Digital Universe Guide - Hayden Planetarium

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110 3. THE MILKY WAY ATLAS 3.3.20 Galactic Coordinates Sphere Group Name galac Reference — Prepared by Brian Abbott (AMNH/<strong>Hayden</strong>) Labels Yes Files galac.speck Dependencies none Once astronomers understood the structure of our Galaxy in the early part of the 20th century, it was necessary to devise a coordinate system based on that structure. Galactic coordinates are defined by Galactic longitude, ℓ, and Galactic latitude, b, measured in degrees. The “equator” coincides with the plane of the Galaxy. Galactic longitude is measured from Galactic center, which is generally in the direction of Sagittarius A ∗ , a compact radio source that astronomers now know to be about 5 arcminutes from the Galactic nucleus. The north Galactic pole (b = +90 ◦ ) lies in the constellation Coma Berenices, while the south Galactic pole (b = −90 ◦ ) is in the constellation Sculptor. These points are perpendicular to the plane of the Galaxy. If you look toward these points in the sky, you are looking directly out of the Galactic plane. Because there are not as many stars or much gas and dust in this direction, we can see objects to greater distances when we look toward the Galactic poles. Other galaxies and clusters of galaxies are easier to find in these regions of the sky. In the Atlas, we have given the Galactic coordinates a greenish color. Labels appear every 10 ◦ in both ℓ and b. The sphere has a radius of 1,000 light-years.
3.3. MILKY WAY DATA GROUPS 111 3.3.21 Visible All-Sky Survey Group Name mwVis Reference Axel Mellinger (Universitaet Potsdam) Prepared by Ryan Wyatt (AMNH/<strong>Hayden</strong>) Labels No Files mw-visible.speck Dependencies mellinger-optmw.sgi Wavelength 400 nm − 700 nm Frequency 750,000 GHz − 430,000 GHz In ancient times, our ancestors knew of the stars, the “wandering stars” (planets), and the Milky Way. Aside from the occasional comet, “guest star” (supernova), or aurora, these were the only cosmic features visible to them. The Milky Way has been the subject of many myths and legends. The Greeks believed it to be a river of milk pouring from the breast of Hera, the wife of Zeus, and called it a “galaxy,” from the Greek word for milk. The Romans called it the Via Lactea, or the Milky Way. But it was not until 1610 that Galileo first observed this faint band of light with his telescope, discovering that it was composed of innumerable faint stars. In the past 400 years, astronomers and philosophers have speculated about the nature of this star system. It was not until the 20th century, though, that astronomers began to understand the nature and structure of our Galaxy, by looking at that band of light across our sky and comparing it with other “island universes,” like the Andromeda Galaxy. Image Features Several features of this band of light become obvious upon inspection (particularly if you increase its alpha value using the Alpha Slider). You will see the brightest part of the Galaxy if you look toward Galactic center [turn on the Galactic coordinates (galac) and bring (l, b) = (0, 0) ◦ to center screen]. In this direction, looking toward Scorpius and Sagittarius, is the center of the Galaxy. The bright haze is the light from millions of stars; the dark lanes are foreground dust, obscuring our view. Relative to the rest of the Milky Way band, the center forms what astronomers call a “bulge” of light (see group bulge for size), whereas the rest of the band appears thinner. If you turn to look in the opposite direction, toward Orion [(l, b) = (180, 0) ◦ ], you will see that the Milky Way is not too bright on this side of the sky. Here we look out of the Galaxy through what remains of the Galactic disk between the Sun and its outer edge.
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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 51 to
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3.2. MILKY WAY ATLAS TUTORIAL 57 bi
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Page 145 and 146: 4 The Extragalactic Atlas The word
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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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