The Caldwell Objects

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84 8 4 NGC 5286 Type: Globular Cluster Con: Centaurus RA: 13 h 46 m 26.5 s Dec:-51° 22'24" Mag: 7.3; 7.2 (O'Meara) Diam: 11' Dist: 36,000 light-years Disc: James Dunlop, included in his catalog of 1827 J. H ERSCHEL: Very bright; gradually much brighter to the middle; 2.5' or 3' diameter; resolved into 15th magnitude] stars; has one star [of] 12th magnitude south following [to the southeast]; the centre near the edge. It is in the field with Brisbane 4618 a star of 6th magnitude]. (h3533) NGC 5286 is ONE OF THE SKY' S BRIGHTEST, yet most neglected, globular clusters. It is easily located just 5° southeast of the great globular cluster Omega Centauri (Caldwell 80), where it lies directly between magnitude-2.6 Zeta (ζ) and magnitude-2.3 Epsilon (ε) Centauri, though a bit closer to the latter. The cluster literally hides in the blinding topaz glare of 4.6-magnitude Μ Centauri just 4' to the southeast. (M Centauri is a rather complex star, being a double with a magnitude-4.6, type-G8III primary and an llthmagnitude secondary — a suspected variable star; and a spectroscopic binary.) NGC 5286 is also part of a 2½°-long binocular asterism that looks like the constellation Scorpius. Shining at magnitude 7.3, the cluster is as bright as, or brighter than, about half of the Messier Catalog's 29 globulars. Is it any wonder, though, that Omega Centauri steals all the attention in this region of sky? 336 GC: Globular cluster, very bright, pretty large, round, well resolved, stars of magnitude 15 and fainter. NGC: Globular cluster, very bright, pretty large, round, well resolved, stars of magnitude 15. Aside from some of its physical parameters, little is known about the nature of NGC 5286. It has a normal globular-cluster metallicity, with each of its member stars having, on average, nearly 1/50 as much iron (per unit of hydrogen) as does our Sun. The cluster has an integrated spectral type of F5. Helen Sawyer Hogg listed eight variable stars in NGC 5286 in 1973, and William Liller increased that number to 16 five years later. All are apparently RR Lyrae types. A 1995 study of the cluster by Nikolai Samus (Institute of Astronomy of the Russian Academy of Science) and his colleagues determined an age between 14 and 18 billion years for the cluster, with the likeliest value being 17 billion years. This finding remains quite controversial, however, both because the cluster has been insufficiently studied and because recent estimates of the Hubble Constant and other cosmological parameters Deep-Sky Companions: The Caldwell Objects
suggest that our universe may be only 12 or 13 billion years old. NGC 5286 lies 28,000 light-years from the galactic center and 36,000 light-years from the Sun. In brightness, apparent size, and distance, NGC 5286 resembles M68 in Hydra. The cluster is moving toward us at 58 km per second, a quarter of Omega Centauri's radial velocity. Interestingly, if you were to reel NGC 5286 in to Omega Centauri's distance, NGC 5286 would still appear about 2.5 times smaller, and 10 times fainter, than that great cluster. James Dunlop discovered this cluster from Australia with a 9-inch reflector. It is listed as the 388th object in his 1827 catalog. Of it he writes: "A bright exceedingly well-defined rather elliptical nebula, about 1' diameter, exceedingly condensed almost to the very edge, and gradually a little brighter to the centre. This is about 6' north of Μ Centauri. — I have strong suspicion that this is resolvable into stars." From Hawaii I can see Μ Centauri with the unaided eye but I could not resolve the cluster next to it. I do not think it impossible to do so, however, especially for someone who observes from the Southern Hemisphere with younger eyes than mine. The globular reveals itself with the slightest of aperture. In 7x35 binoculars it 84 looks like a tiny ghost image of Μ Centauri, a dim puff of smoke wafting away from that alluring flame-colored star. At 23x in the 4-inch, the color contrast between the two objects is remarkable. Μ Centauri looks strongly yellow with a tinge of orange — like a dim Arcturus— while the globular cluster glimmers with a very pale ashen blue. Still, at this low magnification little else can be seen; the cluster looks like a circular wafer of uniform light, a breath spot on a mirror. The late, great comet discoverer Jack Bennett of South Africa included NGC 5286 as the 64th entry in his list of objects that looked cometlike through a 5-inch rich-field refractor. Indeed, I have spotted NGC 5286's misleadingly cometary form several times in my own comet sweeps of the Centaurus area. At 72x NGC 5286 appears as a moderately condensed glow with stumps of starlight poking out at the cardinal directions in a cruciform shape. These are probably the "faint star points" that Ernst Hartung glimpsed with his 4-inch telescope. The cross lies on an elliptical bed of fainter suns. Under a dedicated gaze, star patterns seem to spiral out from the cluster's condensed core, which appears very mottled or patchy, as it is interspersed with dark veins. This view is rather reminiscent of Dunlop's discovery impression. And Dunlop's "strong suspicion" that this cluster would resolve into stars was most certainly justified. Although NGC 5286's horizontal-branch magnitude is 16.5, the cluster's brightest stars shine at a respectable magnitude of 13.5, so partial resolution can be obtained in good telescopes with apertures as small as 3 inches. At high magnifications the cluster sports some seven arms. Two of them — one to the south and one to the east — form a counterclockwise spiral. The other arms look more rigid. Each is dappled by a few 13th- and 14th- The Caldwell Objects 337
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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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Northern Hemisphere, and people cel
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magnitude field star 2' to the nort
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this state of affairs.) The Hyades
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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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4 7 NGC 6934 Type: Globular Cluster
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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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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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Page 315 and 316: times larger than the full Moon. In
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Page 321 and 322: NGC 6231). Under averted vision the
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Page 357 and 358: 8 5 Omicron Velorum Cluster IC2391
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Page 363 and 364: 8 7 NGC 1261 Type: Globular Cluster
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Page 371 and 372: fact, if you look about 7' southwes
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Page 375 and 376: NGC 2867 is a nitrogen-rich planeta
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Page 379 and 380: 9 2 Eta Carinae Nebula GC 3372 Type
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Page 399 and 400: 9 5 NGC 6025 Type: Open Cluster Con
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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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104 NGC 362 Type: Globular Cluster
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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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107 NGC 6101 Type: Globular Cluster
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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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The Caldwell Objects

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