The Caldwell Objects

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100 T HOSE WHO OWN COPIES OF THE ORIGINAL Caldwell Catalog will find the data table accompanying this text somewhat perplexing. In the original catalog Caldwell 100 is listed as the magnitude-4.5 open cluster IC 2944, and it is also called the Gamma Centauri Cluster. But this cannot be. First of all, there is no star cluster associated with Gamma Centauri. The cluster's Caldwell Catalog position makes that point clear, for it is centered on a spot just 5' east of Lambda Centauri — which does appear to have a large, loose cluster associated with it. Patrick Moore simply mistook Lambda (λ) for Gamma (γ). Okay. But the problem does not end there. According to Brian Skiff and Brent Archinal, IC 2944 is not the Lambda Centauri Cluster. Rather, it is the nebula surrounding the Lambda Centauri Cluster. And the cluster's proper name is Collinder 249. Mystery solved? Not exactly. After receiving this information I looked at these objects on several star atlases and in catalogs and discovered the following curiosities: 398 The 1962 edition of the Skalnate Pleso Atlas of the Heavens and the 1981 edition of Wil Tirion's Sky Atlas 2000.0 plot IC 2944 as a small nebula immediately surrounding Lambda Centauri, with a slight elongation to the northwest. No cluster is shown with Lambda Centauri, though an open cluster labeled IC 2948 is plotted about ½ ° to the southeast of the star. Uranometria 2000.0 depicts IC 2944 as a cluster of stars immediately to the east of (and including) Lambda Centauri. IC 2948 is depicted as a nebula that surrounds Lambda Centauri and flows to the south and southeast, as well as a bit to the northwest, of that star. The Deep Sky Field Guide lists IC 2944 as a magnitude-4.5 open cluster southeast of Lambda Centauri and IC 2948 as a nebula surrounding this entire region. Sky Catalogue2000.0 lists IC 2944 as a 15'-wide cluster centered on the original Caldwell Catalog position, roughly 5' east of Lambda Centauri. The Millennium Star Atlas shows IC 2948 as a nebula surrounding Lambda Centauri and extending nearly a full degree to the south and southeast. It does not show any star clusters in the area. The second (1998) edition of Sky Atlas 2000.0 also depicts IC 2948 as a nebula surrounding Lambda Centauri and the regions to the south and southeast. But it also shows IC 2944 as a tiny cluster that seems to include Lambda Centauri, though it is centered on a point just southeast of that star. What's going on? If the cluster's proper name is Collinder 249, why isn't this designation mentioned in catalogs or plotted on star charts? Better yet, exactly where is the Lambda Centauri Cluster, since so many references are in disagreement? And finally, just what is the difference between IC 2944 and IC 2948, if indeed there is one? I turned to Archinal for help, and he solved the mystery by checking the sources for the original data for IC 2944, IC 2948, and Collinder 249. Here's what he reports: IC 2944. The IC lists this as Frost 789 with the following description: "star of magnitude 3.4 in an extremely large nebula." The Deep-Sky Companions: The Caldwell Objects
position updates to (2000.0) R.A. 11 h 35.7 m and [Dec] -63° 01’; the range updates to approximately (2000.0) from IP 35 m to IP 36 m, and from -62° 47' to -63° 13'. The [Digitized] Sky Survey shows at this position a very bright star (Lambda Centauri), and faint nebulosity around it that is mostly overpowered by the star. There is also a very rich background of stars here, which may be a cluster. IC 2948. The IC lists this as Frost 790 with the following description: "Most extremely large." In the Harvard Annals, Frost 790 is described as a "Neb. patch ext. from 11 h 30.6 m to IP 38.l m, and from -62° 28' to -63° 14'." The position updates to (2000.0) [R.A.] IP 38.8 m, [Dec] -63° 31' and the range updates to approximately (2000.0) from 11 h 35 m to 11 h 43 m and from -63° 01' to -63° 47'. At the precisely given position, the DSS shows nothing unusual. However, with histogram equalization [an image-processing technique], there are concentrations of nebulosity to the northwest, north-northeast, and northeast. Α 1° DSS image shows nearly the full 1° square filled with nebulosity, with the patches mentioned above being the brightest portions. Clearly, [Yerkes Observatory astronomer Edwin Brant] Frost [(1866-1935)] had the whole area in mind and not just the brighter concentrations. It is also clear that this is the (larger) nebulosity to the southeast of IC 2944 and is not IC 2944 itself. Cr 249. Collinder 249 is listed by Collinder as IC 2944 (more comments on this follow). He describes it as 40' x 15' in size, 2.7 total magnitude, and 25 stars total. He adds that Lundmark lists it as 65' x 40' in size, 2.9 total nebulosity. Areal density of fainter stars the same as in surroundings (from star-counts)." Collinder goes on to present a photo- graph of this cluster, copied from the Franklin- Adams charts, showing several bright stars in nebulosity. I couldn't easily match this photo to a DSS image of the area, so I checked the Franklin-Adams chart (no. 18). I was surprised to find that Cr 249 in fact is a very large object, consisting of all of the stars around IC 2944 and IC 2948, and then some! Generally it is the whole group of stars extending from Lambda Centauri (and IC 2944) on the northwest, down to a pair of stars at 11 h 41.8 m and -63° 49', thus filling [an] oval about 1 degree in length! Lundmark's size estimate of 65' x 40' thus matches well. Thus, Collinder 249 is not IC 2944. Frost mentioned nothing about a star cluster in his descriptions of either IC 2944 or IC 2948. And more importantly, the group of stars is centered on IC 2948 and not IC 2944 as Collinder's identification and (incorrect) position implies. These two errors by Collinder are obviously the source of all the later confusion about the objects here. In summary, the nebula IC 2944 is pretty much concentric on Lambda Centauri. IC 2948 is the nebulosity to the southeast, and it is distinct from IC 2944. And the entire area's ensemble of stars is the cluster Collinder 249. There apparently is no cluster centered on Lambda Centauri, though it does have a rich background of Milky Way stars. (Incidentally, Lambda Centauri itself is much closer than the cluster; the Hipparcos satellite has pegged its distance at 410 light-years.) magnitude, and 40 stars total. It is called a Another Caldwell mystery solved! Despite "Neb. cl." so the involved nebulosity was its tortured history, and the way it has been mis- clearly recognized. Collinder calls it " replica A represented on star charts, we can now engage in Southern Sky of Pleiades" and writes, "This is a chain of bright stars with 100 ourselves in finding the true Lambda Centauri Cluster with confidence. (Any nebulosity seen The Caldwell Objects 399
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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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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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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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Page 365 and 366: timates, making it 2 billion years
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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 399 and 400: 9 5 NGC 6025 Type: Open Cluster Con
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Page 427 and 428: 104 NGC 362 Type: Globular Cluster
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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Page 453 and 454: 7 N G C 4 0 4 T y L p e n : G t a i
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Page 461 and 462: 19 N G C 6 2 8 1 T y O p e C : n l
Page 463 and 464: 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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