The Caldwell Objects

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30 3 0 NGC 7331 Type: Spiral Galaxy (Sbc) Con: Pegasus RA: 22 h 37.1 m Dec: +34° 25' Mag: 9.5 Dim: 9.7 x 4.5' SB: 13.3 Dist: 47 million light-years Disc: William Herschel, 1784 W. H ERSCHEL: [Observed 5 September 1784] Very bright, considerably large, much extended. Much brighter in the middle. Resolvable. (Η I- 53) GC/NGC: Bright, pretty large, pretty much extended toward position angle 163°, suddenly much brighter in the middle. WHEN THE LAVENDER CURTAIN OF DUSK FALLS toward the western horizon in mid-December, the mythical winged horse Pegasus vaults high across the meridian. Many observers find this an opportune time to hunt down the great globular cluster Μ15 within sniffing distance of Enif, the star marking the Horse's nose, or 118 the Andromeda Galaxy, M31, which immediately follows the Horse across the sky. But about 4½° north-northwest of Eta (η) Pegasi, "beneath" the flying Horse's front legs, lies another magnificent, though often overlooked, spiral galaxy: NGC 7331. From dark skies this galaxy can be glimpsed as a dim slash of light in 7x35 binoc- Deep-Sky Companions: The Caldwell Objects
ulars; challenge yourself and your friends to hunt it down this way at your next star party. NGC 7331 belongs to the Pegasus Spur of galaxies, a small gathering of 35 systems that includes one member of the famous Stephan's Quintet (described below). NGC 733l's spiral disk is tilted 22° from edge on. It whisks away from the solar system at a generous 820 km per second. In detailed photographs the galaxy looks like an oblique aerial view of a hurricane at night; the glowing eye and spiral arms of the "storm" seem poised to snuff out the lesser stellar metropolises surrounding it. The galaxy's modest apparent size and brightness belie its true enormity. In fact, NGC 7331 is among the largest galaxies known. If we accept a distance of 47 million light-years (a value that has been verified by the Hubble Space Telescope), NGC 733l's linear diameter becomes 130,000 light-years. NGC 7331 appears to have a total mass of 300 billion Suns. Thus it equals in size and mass the great Andromeda Galaxy and outranks our Milky Way. As early as 1961, astronomers recognized that NGC 733l's structure is less like that of M31 and more like that of M63 in Canes Venatici or NGC 2841 in Ursa Major (though NGC 733l's spiral arms appear thicker and are more easily seen than those of the latter two galaxies). NGC 7331 is now classified as an Sbc galaxy, meaning it is a spiral with somewhat tightly coiled arms, a relatively small nucleus, and no bar. Spectroscopic data indicate that there has been large-scale star formation in NGC 733l's nucleus. Spectroscopy and photography also have helped astronomers determine which side of the giant spiral is closer to us. The data suggest that the northern end of the spindle is approaching us and that its western side — the one marked by the especially prominent dust lane — is closer; the spiral arms are trailing. The stars in the central 3" The Caldwell Objects 30 (650 light-years) of the galaxy's disk, while relatively young (about 2 billion years old), are very rich in "metals" (the chemical elements, heavier than helium, that stars produce via nuclear fusion). This region might represent a circumnuclear ring formed during a recent starburst episode. NGC 733l's starlike nucleus also probably experienced a secondary starformation burst because, at an age of about 5 billion years, it is two to three times younger than the surrounding bulge. Rosat made the first deep X-ray observations of NGC 7331, and in the process discovered a nuclear X-ray source — a finding that bolsters the notion of a massive black hole at the galaxy's heart. In turn, that black hole may somehow be related to NGC 733l's modest low-ionization nuclear emission-line region, or LINER. It is curious that William Herschel believed that he had resolved NGC 7331. But as Larry Mitchell points out in Appendix C, Herschel suspected that all nebulae would be resolved into clusters of stars, if only they could be viewed with a sufficiently large telescope. Mitchell says this belief came as a result of Herschel's examination of the Messier objects, which he found either to be made of nothing 119
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DEEP-SKY COMPANIONS The Caldwell Ob
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DEEP-SKY COMPANIONS The Caldwell Ob
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Contents Foreword by Patrick Moore
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to be more difficult than others, s
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years of thought and observation ar
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XII position, type, angular size, a
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sky and share its splendors. There
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CHAPTER 1 About This Book O N ONE S
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times vog can back up and cause a s
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when there is moisture in the air.
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Herschel's original observations, p
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we use today and to one another? I
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SIMBAD (Set of identifications, Mea
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Caldwell 26. The objects in the Cal
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tion near the edges of the charts).
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nights of observing. Unless otherwi
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CHAPTER 2 The Caldwell Objects 1 1
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Because of its location far from th
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as strongly energized as would be e
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suggested by the patchiness of NGC
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4 NGC 7023 Type: Reflection Nebula
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astronomers found direct evidence o
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and his contemporaries. Why then wa
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6 Cat's Eye Nebula NGC 6543 Type: P
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Eighth-magnitude NGC 6543 is locate
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7 NGC 2403 Type: Mixed Spiral Galax
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according to theory, the gas densit
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8 Ghost’s Goblet NGC 559 Type: Op
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One other thing adds to the cluster
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RA: 22 h 56.8 m Dec: +62° 37' Mag:
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nebula is a near impossibility, eve
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1 0 The Horseshoe Cluster NGC 663 T
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heart of the cluster, dividing it i
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appears to be the edge of a rapidly
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1 2 NGC 6946 Type: Mixed Spiral Gal
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to the west by a row of similarly b
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the south-southwest. NGC 457, howev
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photographs. The cluster's bright "
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play begins at 8:00 p.m., when my e
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ightness by summing the contributio
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Page 87 and 88: 15 outer shell falls upon the retin
Page 89 and 90: "knots" have also been noted by exp
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Page 93 and 94: 1 7 NGC 147 Type: Elliptical Galaxy
Page 95 and 96: the center. A faint outer halo is a
Page 97 and 98: 1 9 Cocoon Nebula IC 5146 (nebula)
Page 99 and 100: trickle into the pool surrounding t
Page 101 and 102: 2 0 North America Nebula NGC 7000 T
Page 103 and 104: egion's size and mass extreme when
Page 105 and 106: The Caldwell Objects 20 87
Page 107 and 108: 2 1 Box Galaxy NGC 4449 Type: Irreg
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Page 119 and 120: RA: 03 h 19 m 48 s Dec: +41° 30.7'
Page 121 and 122: Through the 4-inch, NGC 1275 is les
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Page 125 and 126: 26 Silver Needle Galaxy NGC 4244 Ty
Page 127 and 128: 2 7 Crescent Nebula NGC 6888 Type:
Page 129 and 130: Observatory, England) still lists a
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Page 133 and 134: 29 NGC 5005 Type: Mixed Spiral Gala
Page 135: s h a edges. r p However, Christian
Page 139 and 140: NGC 7331 is extended much farther t
Page 141 and 142: away" stars escaped the confines of
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Page 145 and 146: highly suspect by some. However, in
Page 147 and 148: 33 Network Nebula; Bridal Veil Nebu
Page 149 and 150: A quarter-second later, the star en
Page 151 and 152: under the dark skies of Seagrave Ob
Page 153 and 154: 35 NGC 4889 Type: Elliptical Galaxy
Page 155 and 156: magnitude 12.2 some 18' to the east
Page 157 and 158: 36 NGC 4559 Type: Mixed Spiral Gala
Page 159 and 160: Comae Berenices, the obvious northe
Page 161 and 162: 3 7 NGC 6885 Type: Open Cluster Con
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Page 177 and 178: 4 0 NGC 3626 Type: Lenticular Galax
Page 179 and 180: 40 NGC 4546 in Virgo, NGC 4138 in C
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4 2 NGC 7006 Type: Globular Cluster
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each square arcminute of its disk s
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4 3 Electric Arc NGC 7814 Type: Spi
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hook as my "train route." Start at
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230 billion Suns and a physical dia
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4 5 NGC 5248 Type: Mixed Spiral Gal
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of the field. Those living under da
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1" in a mere four days. Clearly, La
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porarily) even the most practiced o
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stragglers are stars that appear to
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4 8 NGC 2775 Type: Spiral Galaxy (S
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with a CCD camera — discovered a
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this wreathlike network of dust and
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fuzzy patch of light with the unaid
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known as NGC 2244; and NGC 2239 sho
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At a glance the two stars at the cl
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On four plates taken with the Bruce
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years. A total of 43 star-cluster c
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5 2 NGC 4697 Type: Elliptical Galax
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northeast of the sixth star in the
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53 The Spindle NGC 3115 Type: Lenti
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and the 100-inch telescopes atop Mo
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5 4 NGC 2506 Type: Open Cluster Con
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emerge, followed by a diffuse outer
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perfection than is actually the cas
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jets, like a stream of water from t
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5 6 Pac-Man Nebula NGC246 Type: Pla
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the triple-alpha process, wherein t
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5 7 Barnard's Galaxy NGC 6822 Type:
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to show how the galaxy's western re
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core and limber arms, which, he wro
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esembles Jupiter . . . '" Smyth's f
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years" and suggests amateurs monito
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6 0 Ringtail Galaxy; Rataail Galaxy
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war. X-ray images taken by the Rosa
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W. Sinnott's NGC 2000.0 has a visua
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62 Milkweed Seed Galaxy NGC247 Type
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through the narrow haze. But give t
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was more readily seen in binoculars
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Society. Accepting that distance, w
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any large telescope that can provid
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ought it to our attention in the Fe
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inch the cluster shows a pyramid of
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NGC 253 is the brightest member of
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magnitude stars, one just to the ea
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6 6 NGC5694 Type: Globular Cluster
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you see its core dancing? Its starl
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cosmologist Halton Arp (Max-Planck
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and kinked. All this detail is wrap
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telescope. But seeing it takes more
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streamers begin to appear, but they
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tounding, because NGC 6302 is a mag
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70 Southern Pinwheel NGC300 Type: S
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would John Herschel suddenly fault
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Dunlop discovered NGC 55 with his 9
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even when crossing the meridian. Co
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"nebulous clusters" (Class II); and
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galaxy's disk and halo. NGC 2477 ap
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condensed, almost to the very margi
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The asymmetry remains at high power
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other popular nickname, the Eight-B
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longed look, the object displays a
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times larger than the full Moon. In
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emains of a globular cluster that w
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he classified them accordingly. NGC
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NGC 6231). Under averted vision the
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7 7 Centaurus A NGC5128 Type: Pecul
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Harvard College Observatory's 24-in
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at 16 million light-years. If you s
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78 NGC 6541 Type: Globular Cluster
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seems to fragment into tiny stars,
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sense, evinced by any known cluster
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12th-magnitude double star. The clu
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original with Bayer, but goes back
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Omega Centauri is generally regarde
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glitter all come to mind as the clu
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shattered remains of their diminuti
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It's a nice even disk of l0th-magni
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with the fiery reddish light of hyd
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nebulosity when he viewed the regio
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the two jets of radio-wave-emitting
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pair of tweezers. A fairly bright s
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suggest that our universe may be on
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8 5 Omicron Velorum Cluster IC2391
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Nicolas Louis de Lacaille, however,
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much sky as does the full Moon, tho
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timates, making it 2 billion years
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NGC 5822. Don't be surprised if you
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89 S Normae Cluster NGC 6087 Type:
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fact, if you look about 7' southwes
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lowing night fell clear, when Hersc
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NGC 2867 is a nitrogen-rich planeta
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halfway between M37 in Auriga (200
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9 2 Eta Carinae Nebula GC 3372 Type
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anch of cold, dark material. Indeed
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stretch 16 billion km from the cent
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the object was known to some civili
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east, and a dim lip of gas to the s
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1 0 1 NGC 6744 Type: Barred Spiral
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have been identified in NGC 6752's
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ightest spiral arm(s) to the north,
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his maiden voyage of discovery in 1
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simply takes much too much effort t
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very wide double of near-equal inte
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went out and looked at the cluster
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NGC 2516 is 60 million years young
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and contains some 1,890 members, wh
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9 8 Coalsack Cluster NGC 4609 Type:
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it near the Swan? There is a still
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with the naked eye is a challenge.
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1 0 0 Lambda Centauri Cluster Colli
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position updates to (2000.0) R.A. 1
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Eta Carinae Nebula. But remember th
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9th magnitude. Of the latter, 23 ha
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103 1 0 3 Tarantula Nebula; True Lo
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southern-sky explorer Abbe Nicolas
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ters it has had thus far with the g
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ly east of NGC 362 we find the magn
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the eye ever inward and takes your
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1 0 5 Southern Butterfly NGC 4833 T
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stars"). Lacaille also likened NGC
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is about 7' in length, and nearly 2
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evealed a significant blue-straggle
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ightest stars shine around 4th magn
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egion looks cold and disturbing, no
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The galaxy received some incidental
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This entry is obviously in error, b
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7 N G C 4 0 4 T y L p e n : G t a i
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pointed her 7x35 binoculars toward
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13 NGC 288 Type: Globular Cluster C
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your telescope on Eta Sculptoris an
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19 N G C 6 2 8 1 T y O p e C : n l
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C Name Type Con. R.A. Dec Mag. Size
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C Name Type Con. R.A. Dec Mag. Size
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Appendix B Why Messier Did N o t i
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A typical pattern for evening hunti
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Earth turns, the cluster would clim
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Initially Herschel made his living
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of the heavens with it. For his swe
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tube's front end. This meant that t
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Star in Collo Ceti" about the star
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years, Herschel would observe some
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fluid, but added that ages of obser
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Appendix D Photo Credits in order o
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A Abell426, 101 Acrux, 388, 392, 39
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index Caldwell 44, 173, 176-178 Cal
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and nebulae, 271, 274, 362 and open
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Hevelius, Johannes, 72, 81, 452 Hip
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M103, 49-50, 58-59 M110, 77 MACHOs.
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NGC 3324, 369 NGC 3372 (Caldwell 92
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Perseus Cluster, 101 Phi Cas Cluste
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Τ Tarantula Nebula (Caldwell 103),
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