The Caldwell Objects

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97 97 NGC 3766 Type: Open Cluster Con: Centaurus RA: 11 h 36.2 m Dec:-61° 37' Mag: 5.3 Diam: 15.0' Dist: 5,800 light-years Disc: Abbé Nicolas Louis de Lacaille, included in his 1755 catalog J. H ERSCHEL: The preceding of two chief stars of a fine, large, loose, round cluster of stars [of] 8[th to] 12th magnitude]; gradually pretty much brighter in the middle, fills field; 150 [to] 200 stars, (h 3352) H ALFWAY BETWEEN A LPHA (α) C RUCIS, OR Acrux (the foot of the Southern Cross) and the famous Eta (η) Carinae Nebula (Caldwell 92), just 1½° due north of the Lambda (λ) Centauri Cluster (Caldwell 100), and smack-dab on the galactic equator, is yet another young naked-eye open star cluster: NGC 3766 (Caldwell 97). This cluster resides in the Carina molecular complex, a giant collection of molecular-hydrogen clouds that is associated with some of the most massive stars in our galaxy (Eta Carinae among them). Molecularcloud complexes are hotbeds of star formation, and the Carina complex is no exception. It teems with hot, young bodies, including numerous Retype stars (see the Caldwell 10 installment starting on page 49). And NGC 3766 contains the largest number of B e stars known in any single star cluster. A B e star loses mass to an expanding GC / NGC: Cluster, pretty large, pretty rich, pretty compressed, stars of magnitude 8 to 13. shell, and its prodigious rotation draws some of this cast-off matter into a disk surrounding the star's equator. Like their less-massive cousins, the Τ Tauri stars, Be stars are believed to represent the last phase in the pre-main-sequence evolution of young, hot protostars. In brightness, apparent size, and shape, NGC 3766 appears strikingly similar to M37 in Auriga. Each cluster shines at roughly 5th magnitude, measures 15' in diameter, and displays an elongated body flecked with bright suns. Spanning 25 light-years of space, NGC 3766 is 20 percent larger than M37, and though its distance is also greater, by about 1,400 lightyears, NGC 3766 would outshine M37 were it not for interstellar dust, which diminishes its light by a half magnitude. The main differences between the two clusters lie with their ages and stellar populations. M37 is 200 million years old 388 Deep-Sky Companions: The Caldwell Objects
and contains some 1,890 members, while NGC 3766 is a mere 24 million years young with 137 known members (though the larger number of M37 stars may simply be due to that cluster having been studied more often). NGC 3766 is another one of Abbe Nicolas Louis de Lacaille's finds and is listed in his 1755 catalog as the seventh of his Class III objects (stars accompanied by nebulosity). Through his ½-inch 8x telescope Lacaille saw "three faint neighbored stars surrounded by nebulosity." But, as with many of Lacaille's finds, the nebulosity does not exist; it is merely unresolved starlight. Although NGC 3766 is visible to the naked eye under a dark sky, it is not obvious. It lies in a patchy, star-rich section of the Milky Way, and its 5th-magnitude glow requires one to know precisely where to look for it. Particularly deceptive is a 30'-long rectangular asterism oriented north-south; its southern base lies about 15' from NGC 3766's northern fringe. This clusterlike grouping looks larger and fuzzier to the naked eye than does NGC 3766, and it could be mistaken for 97 our tiny target. It's best first to identify NGC 3766 in binoculars, then to look with the naked eye. In 7x35 binoculars its half-dozen brightest suns form a sideways Τ that stands out at the northwestern end of a roughly l⅓°-long chain of four similarly bright, equally spaced stars. This chain starts about 1° northeast of Lambda Centauri and continues northwestward toward NGC 3766. At 23x in the 4-inch Genesis the cluster's brightest stars are colorful 8th- to l0th-magnitude jewels strewn across a carpet of dim, white suns. James Dunlop first noted the star's colors in the 1820s, writing: "The greater number of the stars are of a pale white colour. There is a red star near the preceding [western] side; another of the same size and colour near the following [eastern] side; another small red star near the centre; and a yellow star near the south following [southeastern] extremity, all in the cluster." And modern observers still comment on them: in Volume 7 of the Webb Society Deep-Sky Observer's Handbook, NGC 3766 is described as having some "orange and yellow The Caldwell Objects 389
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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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"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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Page 371 and 372: fact, if you look about 7' southwes
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Page 379 and 380: 9 2 Eta Carinae Nebula GC 3372 Type
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Page 415 and 416: 1 0 0 Lambda Centauri Cluster Colli
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Page 429 and 430: ters it has had thus far with the g
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Page 435 and 436: 1 0 5 Southern Butterfly NGC 4833 T
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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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