The Caldwell Objects

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49 & 50 4 9 Rosette Nebula; The Great Nebula in Monoceros; Swift’s Nebula NGC 2237-8,46 Type: Emission Nebula Con: Monoceros RA: 06 h 32.3 m Dec: +05° 03' Mag: ~5, northwestern segment (O'Meara) Dim: 80' x 60' Dist: 4,900 light-years Disc: (in pieces) Albert Marth, 1864; Lewis Swift, prior to 1883 (independent- ly by Edward Emerson Barnard, 1883); Swift, 1886; and Barnard, 1890s H ERSCHEL: None. GC: None. 5 0 NGC 2244 Type: Open Cluster Con: Monoceros RA: 06 h 32.3 m Dec: +04° 51' Mag: 4.8; 4.4 (O'Meara) Diam: 30' O NE OF THE HEAVENS' MOST OBSCURE constellations is dim Monoceros, a sprawling array of inconspicuous suns east of Orion. Of its more than 60 naked-eye stars, none shines brighter than magnitude 3.9; the constellation is as elusive as the mythical unicorn it repre- 194 NGC (2237): Pretty bright, very large, diffused, part of extremely large nebulous ring around [open cluster] NGC 2239 [= NGC 2244]. Dist: 4,900 light-years Disc: William Herschel, 1784 W. H ERSCHEL: [24 January 1784] A beautiful cluster of scattered stars, chiefly of two sorts. The first large, the second arranged in winding lines, contains the 12th Monoc [12 Monocerotis]. (H VII-2) GC: None. NGC: Cluster, beautiful, stars scattered (12 Mon). sents. But halfway between the unicorn's nose and eye (8 and 13 Monocerotis, respectively), and just a jog to the southeast, we find the Great Nebula in Monoceros (Caldwell 49), one of the largest and most massive nebulae in the night sky. Better known as the Rosette Nebula, Deep-Sky Companions: The Caldwell Objects
this wreathlike network of dust and gas is about as large as M42, the Orion Nebula, on the plane of the sky. But it is more than three times as far as M42, and therefore that much larger intrinsically; at its greatest extent the Rosette spans nearly 115 light-years, while the Orion Nebula spans only 40 light-years. In photographs the Rosette appears to ripple outward from a central hollow, as if a stone had been dropped into a pool of celestial vapors. A more elegant metaphor might be a snow-dusted rose seen by the frosty light of the Moon. The Rosette Nebula surrounds the rectangular open cluster NGC 2244 (Caldwell 50), whose 100 members populate the nebula's ½°wide central cavity. (Note that the position given in the table on page 194 is for 12 Monocerotis. That star appears to be on the southeastern end of the cluster's densest portion. But that is an illusion. Cluster members do extend farther to the southeast, though they are swaddled in nebulosity. Taking these "hidden" suns into consideration, Brian Skiff estimates that 12 Monocerotis marks the cluster's center as projected onto the plane of the sky.) Collectively these stars shine at magnitude 4.8, say sources, so they make a reasonable naked-eye target (and my own estimate makes them 0.4 magnitude brighter still). Ultraviolet radiation streaming from the cluster's young, hot stars excites the surrounding nebula, whose spectrum shows strong emission lines of hydrogen and singly ionized oxygen as well as the so-called "forbidden" blue-green lines of doubly ionized oxygen. But, unlike the cluster, the Rosette Nebula burns brightly only in photographs. Visually the nebula is dim and challenging, and while some have seen it with the unaided eye (myself included), others have argued that seeing it without optical aid is as likely as seeing a unicorn in New York City. But more on that later. Glance at almost any photograph of the 49 & 50 Rosette and you'll see dark veins of obscuring matter peppering the nebula's northwestern quadrant; it's as if someone had spray-painted the nebula with celestial graffiti. Magnified views of these features reveal the presence of tiny dark blobs. These blobs are known as Bok globules after the late Harvard College Observatory astronomer Bart J. Bok, who turned astronomers' attention to them in the late 1940s. (Bok called them "globules" because they reminded him of the small globules of fat floating atop the cream that the H.P. Hood Company delivered to his Belmont, Massachusetts, home.) Bok proposed that these diminutive dark masses, which span less than 10,000 a.u., were once attached to umbilical filaments of neutral hydrogen gas. Radiation from nearby stars separated, then compressed, them, and the orphaned dark clouds continued to contract under their own gravity until they formed the tiny globules we see today. These small black orbs may be crucibles of creation, for they are the primeval dust clouds within which new suns and new worlds may be forming. By studying Bok globules, we stand at the threshold of understanding the origins of new solar systems. Indeed, life itself may have been conceived within the confines of dusty cocoons like these. The visual gem of the nebulous Rosette complex, however, is NGC 2244, the dazzling cluster at its heart. The cluster's physical diameter is 43 light-years. It is very young on the cosmic time scale, having formed within the Rosette Nebula less than 1 million years ago (about when the Trapezium stars formed in the Orion Nebula). More than 3 million years before these stars burned through their cocoons, the first hominids already had appeared on Earth. And by the time these stars bathed the Earth with their light, Homo erectus had migrated out of his native Africa and ventured The Caldwell Objects 195
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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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jewels. Here are sapphires, rubies,
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15 outer shell falls upon the retin
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"knots" have also been noted by exp
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tight gathering of a half-dozen rou
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1 7 NGC 147 Type: Elliptical Galaxy
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the center. A faint outer halo is a
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1 9 Cocoon Nebula IC 5146 (nebula)
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trickle into the pool surrounding t
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2 0 North America Nebula NGC 7000 T
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egion's size and mass extreme when
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The Caldwell Objects 20 87
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2 1 Box Galaxy NGC 4449 Type: Irreg
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fuse but obvious glow of patchy lig
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qualifier—the word "light" — ha
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with a sheen of light, especially a
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1003, NGC 1023, and NGC 1058 (a nic
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Way) that pop in and out of view as
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RA: 03 h 19 m 48 s Dec: +41° 30.7'
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Through the 4-inch, NGC 1275 is les
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(300,000 light-years), Pal 4 (360,0
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26 Silver Needle Galaxy NGC 4244 Ty
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2 7 Crescent Nebula NGC 6888 Type:
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Observatory, England) still lists a
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pie refractors and inefficient spec
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29 NGC 5005 Type: Mixed Spiral Gala
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s h a edges. r p However, Christian
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ulars; challenge yourself and your
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NGC 7331 is extended much farther t
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away" stars escaped the confines of
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sweep the telescope in a north-sout
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highly suspect by some. However, in
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33 Network Nebula; Bridal Veil Nebu
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A quarter-second later, the star en
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under the dark skies of Seagrave Ob
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35 NGC 4889 Type: Elliptical Galaxy
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magnitude 12.2 some 18' to the east
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36 NGC 4559 Type: Mixed Spiral Gala
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Comae Berenices, the obvious northe
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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
Page 181 and 182: Northern Hemisphere, and people cel
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Page 187 and 188: 4 2 NGC 7006 Type: Globular Cluster
Page 189 and 190: each square arcminute of its disk s
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Page 197 and 198: 4 5 NGC 5248 Type: Mixed Spiral Gal
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Page 205 and 206: 4 7 NGC 6934 Type: Globular Cluster
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Page 209 and 210: 4 8 NGC 2775 Type: Spiral Galaxy (S
Page 211: with a CCD camera — discovered a
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Page 219 and 220: At a glance the two stars at the cl
Page 221 and 222: On four plates taken with the Bruce
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Page 241 and 242: 5 6 Pac-Man Nebula NGC246 Type: Pla
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Page 245 and 246: 5 7 Barnard's Galaxy NGC 6822 Type:
Page 247 and 248: to show how the galaxy's western re
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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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8 7 NGC 1261 Type: Globular Cluster
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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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9 5 NGC 6025 Type: Open Cluster Con
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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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