The Caldwell Objects

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53 brighter centre, bearing magnifying unusually well." And indeed it does. At 72x the galaxy's nucleus looks layered, evincing a bright core surrounded by an oval haze. A sharply defined plane extends from either side of this inner halo, recalling Saturn with its rings edge on. Concentrate on the outer edges of this "ring plane." Do you see some fuzzy patches? High power brings out a fantastic sight. The galaxy's core is sharply defined, with a brilliant stellar bead embedded in a lens of light. A fainter, though obvious, oval halo surrounds the interior lens, then tapers alongside the razor-sharp linear extensions, which emanate from either side of the lens. The northeastern extension does not appear to connect to the lens, while the southwestern one does. Does this imply the presence of dust? Barbara Wilson suspected a dust lane on the galaxy's southern side, and I can understand why; the region just outside the 214 inner lens is not as bright as the outer half of the lens. Dust may be responsible for this. The details seen in NGC 3115 through small instruments certainly rival those obtained with larger telescopes, as Houston noted: "I think it fascinating to find an object that shows well in 5inch binoculars, looks similar in a 12-inch instrument, and still perplexes professional astronomers working with the largest telescopes in the world." A magnitude-11.5 star lies 3.3' south of NGC 3115's core; it "balances" on the lip of the galaxy's outer halo. Note that a 14th-magni-tude star is 1.3' south of the galaxy's center so that you do not mistake it for a supernova. To date only one supernova has been discovered in NGC 3115 (Supernova 1935B), and it appeared about 36" west and 60" north of the galaxy's nucleus. But you always should keep an eye open for "surprise" stars. Deep-Sky Companions: The Caldwell Objects
5 4 NGC 2506 Type: Open Cluster Con: Monoceros RA: 08 h 00.0 m Dec:-10° 46' Mag: 7.6 Diam: 12.0' Dist: 10,000 light-years Disc: William Herschel, 1791 W. H ERSCHEL: [Observed 23 February 1791] A very compressed and very rich cluster of stars. The stars are of two sizes, some considerably large and the rest next to invisible. The compressed part 5’ or 6' in diameter. (H VI-37) GO OUT ON A CLEAR WINTER' S EVENING, when Sirius is sparkling like fire-fused crystal high in the south, and sweep your gaze upward along the winter Milky Way Among its frosty ribbons of starlight are some of the heavens' most magnificent open star clusters, including M46 and M47 in Puppis and M48 in Hydra. And halfway between M46 and M48 lies one of the region's most understated galactic clusters, an old salt of the river Milky Way whose core of aged suns seems like a collection of faded memories. NGC 2506 is among the oldest open clusters known. In 1981, Robert McClure (Dominion Astrophysical Observatory, Canada) and his colleagues derived an age of 3.4 billion years for the cluster, making it a contemporary of M67 in Cancer. More recent studies, however, have dropped that value to about 2 billion years, making NGC 2506 closer in age to NGC 752 (Caldwell 28). Old open clusters are noticeably deficient in "metals," the term astronomers use to de- The Caldwell Objects GC/NGC: Cluster, pretty large, very rich, compressed, stars of 11th to 20th magnitude. 54 scribe all chemical elements heavier than hydrogen and helium. For instance, on average each star in M67 has only 82 percent as much iron as our Sun. Given their roughly comparable ages, one would expect that NGC 2506 might have a similar metal abundance. But it doesn't. NGC 2506 is much poorer in metals than M67, with its average star containing only one-third as much iron as our Sun. Current models of open-cluster formation show that the farther a cluster is from the galactic center, the poorer its metal content. It is the cluster's position in the galaxy, not its age, which determines its metal content. NGC 2506 currently lies near the direction of the galactic anticenter at a relatively high galactic latitude, and it is nearly 10,000 light-years from the galactic center as well as 1,600 light-years above the galactic plane. Together with its position, its low metal abundance places this cluster into a class of objects that includes NGC 2420 (the prototype), NGC 2158, NGC 2204, NGC 2243, and Melotte 66. 215
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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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3 7 NGC 6885 Type: Open Cluster Con
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pressed, stars of magnitude 6 to 11
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of Herschel's telescope. W then e e
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see the dark needle near the third
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sion of a "thin flat ring of enormo
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(which does not appear on Sky Atlas
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not be found in planetary nebulae,
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star in a large naked-eye triangle
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4 0 NGC 3626 Type: Lenticular Galax
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40 NGC 4546 in Virgo, NGC 4138 in C
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Page 185 and 186: this state of affairs.) The Hyades
Page 187 and 188: 4 2 NGC 7006 Type: Globular Cluster
Page 189 and 190: each square arcminute of its disk s
Page 191 and 192: 4 3 Electric Arc NGC 7814 Type: Spi
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Page 197 and 198: 4 5 NGC 5248 Type: Mixed Spiral Gal
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Page 203 and 204: porarily) even the most practiced o
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
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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 225 and 226: 5 2 NGC 4697 Type: Elliptical Galax
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Page 229 and 230: 53 The Spindle NGC 3115 Type: Lenti
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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
Page 249 and 250: 5 8 NGC 2360 Type: Open Cluster Con
Page 251 and 252: core and limber arms, which, he wro
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Page 257 and 258: 6 0 Ringtail Galaxy; Rataail Galaxy
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Page 261 and 262: W. Sinnott's NGC 2000.0 has a visua
Page 263 and 264: 62 Milkweed Seed Galaxy NGC247 Type
Page 265 and 266: through the narrow haze. But give t
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Page 271 and 272: any large telescope that can provid
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Page 277 and 278: NGC 253 is the brightest member of
Page 279 and 280: magnitude stars, one just to the ea
Page 281 and 282: 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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