NGC/IC Project Restoration Effort

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Basic Information

Location and Magnitude

Right Ascension: 10:45:6.0
Declination: -59:52:0
Constellation: CAR
Visual Magnitude:

Historic Information

Discoverer: Lacaille
Year of discovery: 1751
Discovery aperture: 0.5


Summary description: ! Great neb, η Argûs
Sub-type: EN

Corwin's Notes

===== NGC 3372 is the nebula surrounding eta Carinae, or as JH knew it, "eta Argus". I've taken the position to be in the "keyhole", while JH chose the star itself to represent the complex nebulosity; I've given the star separately. Note that the ESO position is nearly twelve arcminutes south at the intersection of the three great wedges of nebulosity that we see on wide field images today ("Pearls of the Southern Sky" by Dieter Willasch and Auke Slotegraaf has just such an image). But this spectacular degrees-wide field of nebulosity is not JH's object; he described, sketched, and catalogued only the brightest, central region.

Steve's Notes

===== NGC 3372 24" (4/11/08 - Magellan Observatory, Australia): this observation of the Homunculus was made at 350x in good seeing with the 24". Eta Carinae appeared an iridescent electric-orange color surrounded by the bipolar blowouts of the Homunculus. The brighter and larger lobe, which is expanding in our direction, extends to the southeast and was pretty circular (a bit flattened on the end), but punctured by a small, elongated hole that splits the lobe near Eta, creating a small 6" loop (connected on the SE end). The NW blowout is fainter and smaller with an unusual "fountain" or "fan" appearance (also referred to as the "paddle" in schematics of the Homunculus), tapering in and dimming to an extremely narrow bridge at Eta and then spreading out to the NW. The NW edge of this lobe is rounder, creating a "fan" appearance. The two lobes create empty notches near Eta and extending into the NE notch between the two lobes is a very thin, short spike (referred to as equatorial debris or "skirt) that was not difficult to view but the SW "spike" was only intermittently visible. Just west of Eta is the fairly prominent, dark "Keyhole Nebula". 18" (7/4/05 - Magellan Observatory, Australia): spectacular detail within the Homunculus nebula at 293x. The bright 6" lobe to the SE of Eta is split by a dark lane (forming the two "legs" of the Homunculus). This lane actually consists of two darker "holes" with the outer dark hole more prominent. In moments of good seeing the outer periphery of the lobe has a slightly tattered or scalloped structure and it is flattened on the SE end. Jutting out a few arcseconds to the NE is a small, thin spike that was visible continuously with averted vision. On the opposite SW side, only a small, brighter extension or oval nodule bulges out slightly from the SE lobe. The fainter NW lobe has a more translucent appearance with a pinched "key" or "bust" outline as the nebulosity is very weak or absent in the middle of the sides (this lobe forms the "head" of the Homunculus). At the center of this remarkable sight is the bright, quasi-stellar, reddish-orange Eta Carinae. Bochum 10 is located 40' NW of Eta Carinae and just north of the huge wedge of nebulosity that extends north of Eta. About two dozen stars, including 7 of 9th magnitude, were resolved in the main group, which extends ~5'x2'. The cluster is fairly scattered and distributed in the two subgroups oriented NW and SE, with the SE group containing most of the stars. Visually it was much smaller than the listed diameter of 20'. Situated just 5' NW of mag 5.4 HD 92964 and just south of the southern arc of the HD 92809 Wolf-Rayet ring, which may be associated with Bochum 10. This huge Wolf-Rayet bubble was surprisingly easy at 76x with an H-beta filter, although without prior knowledge I would have assumed it was an outer extension of the Eta Car nebula. A huge, 35' semicircular annulus of nebulosity was easily traced. The south side of the rim is bright, well defined and oriented roughly E-W as it passes north of Bochum 10. With careful viewing, very faint nebulosity continues to spread out from the east end. On the west side of this E-W strip, there is a short break and then it continues as a large, fairly prominent arc that curves northward. This arc is sharply defined on both the interior and exterior edge and widens and fades at the north end, although a small locally brighter patch is at the NW tip. The nebulosity curves back east on the north side but this section is quite faint and simply appears as low surface brightness haze. A relatively prominent 4'x3' oval patch of nebulosity is isolated on the SE side, just within the interior. Very faint haze also spreads out within the interior but the eastern half of the rim is completely missing. The OIII filter significantly dims the curving NW quadrant of the loop. 13.1" (2/20/04 - Costa Rica): I spent quite a bit of time on the Eta Carina complex, particularly examining the remarkable Homunculus Nebula. This is easily the largest bright emission nebula in the sky and a very prominent naked-eye object within the amazingly rich Carina Milky Way. Dark lanes or rift separate bright islands of billowing nebulosity and the entire complex overfilled the 105x field at the eyepiece. The surface brightness of the various sections is fairly uniform and pretty high, though it lowers in the outskirts. No section is comparable in intensity to the central heart of the Orion Nebula, but the large wedge that contains Eta Car is quite prominent. A UHC filter enhances the nebulosity without significantly dimming the stars. Just west of Eta (within the central wedge) is the fairly prominent, dark "Keyhole Nebula" that extends ~5' length, elongated N-S (not as contrasty as when John Herschel named it in the 1830's). Eta Carina's orange color and the small bipolar blowouts are quite stunning at high power. Several clusters are involved with the nebula. The most prominent is Tr 16, situated just south of Eta Car. Tr 14 is a rich group of ~30 stars mag 7 and fainter stars including the double star h4356 (7.2/8.9 at 2.8", with brighter component HD 93129A) within a 4' diameter. There are several additional mag 8/9 stars and a swarm of mag 12 stars! Tr 14 is situated just 12' NW of Eta Carinae within the bright, huge triangular section of nebulosity to the NW of Eta. The cluster is the second most massive in the Carina nebula and contains ten O-type stars. HD 93129Aa (the brighter spectroscopic component of HD 93129A) is one of the most luminous and massive known stars with ~80-100 solar masses and ~2,500,000 times the sun's luminosity. The "Mystic Mountain" region, a remarkable star-forming pillar of gas and dust captured by the HST, is at the north edge of the cluster. Tr 16 is the most massive cluster in the Carina nebula complex and contains the majority of the O-type stars. Visually, Tr 16 is a rich group of stars trailing immediately south of Eta Carinae itself and close southeast of the dark Keyhole Nebula, all within the same bright triangular wedge. At 166x, about three dozen stars mag 9-13 were resolved within 4'. A number of the stars are arranged in chains and groups. Eta Car itself is considered part of the cluster. Mag 8.8 WR 25 = HD 93162 is about 7' W of center of the cluster. The primary is considered the most luminous known star in our galaxy. Tr 15 consists of roughly 15 stars (a half-dozen members are O-type supergiants) crammed into a 2' group including a neat triple h4364 (mag 8/9/11 at 8" and 9" in a string with brightest member HD 93249) on the north side. Situated within a streamer of nebulosity just 20' NNW of Eta Carina itself. At 200x, the Homunculus Nebula surrounding Eta Carina was remarkable in excellent seeing on the last evening of observing. Both Eta and the nebula were a uniquely vivid color - an amazing fluorescent orange-tangerine. Extending to the SE of Eta is the brighter lobe, perhaps 6" in diameter with a sharp outline that was flattened along the southern edge in a mushroom shape. There appeared to be a partial darker lane in the interior. Extending to the NW was a smaller (4"-5") and much fainter lobe that faded with increased magnification. A tiny spike of nebulosity jutted out along to the NE between the two lobes. A couple of very close and faint companions lie just NE of Eta. This bi-polar reflection nebula resulted from the most recent outburst of supermassive Eta Car in 1841. 20" (7/8/02 - Magellan Observatory, Australia): Using a 20 Nagler (127x) and UHC filter, the field of Eta Carina was a breathtaking sight. The outer wings and streamers extended well outside the 39' field. The turbulent nebulosity had a curdled, electric appearance with a strong 3-dimensional effect as brighter streaks, wings, fainter masses and dark lanes were mixed together throughout the field. The best overall view of the nebula in the 20" was at 80x (32 mm) using a UHC filter. Even at this low power, the Eta Carina nebula still overfilled the field with contrasty dark lanes and amazingly structured islands of nebulosity. I stared into the eyepiece quietly, somewhat stunned by its beauty. With this aperture at 282x, the 12"x8" bipolar Homunculus nebula was an astounding sight. The orange central star appeared quasi-stellar with the unequal blowouts fairly prominent. They had an eerie, translucent appearance with the western lobe somewhat smaller, fainter and more pinched with the eastern lobe more circular. A possible dark lane is near the center and punctures the lobes. Tr 14 is a rich group of stars mag 7 and fainter stars in a 5' region, situated ~12' NW of Eta within one of the sections of nebulosity. Contains the binary h4356 (7.2/8.9 at 2.8"). The brighter spectroscopic member of the mag 7.2 star (HD 93129Aa) is one of the most massive stars known and rivals Eta Car in mass and luminosity. A triple system h4360 just 2' SE includes a 2" pair. Cr 232 is a small, scattered group of ~20 stars in a 4' region just following Tr 14. The brightest star is mag 7.7 HD 93250, a 04-type supergiant. Tr 16, the most massive cluster in the Carina complex, is a triangular group of stars just south of Eta and includes a chain of a half-dozen brighter stars. Tr 15 is a fairly small group of a couple dozen stars mag 8.5 and fainter, less than 30' N of Eta Car. A half-dozen members are O-type supergiants. Cr 228 is a large, scattered cluster ~25' SSW of Eta Carina in the southern part of the complex. It includes two mag 6.5 stars with brightest member 6.2-6.5 QZ Carinae and the Wolf-Rayet star HD 93131. Includes a number of mag 8-9 stars spread over a 15'x10' field. The group is elongated SW-NE. Bochum 10 is a group of two dozen stars in a ~5'x2' region. It includes 7 mag 9 stars that dominate the group. Fairly scattered and distributed in the two subgroups NW and SE with the SE group containing most of the stars. Located just 5' NW of mag 5.4 HD 92964 and just south of the southern arc of the HD 92809 Wolf-Rayet ring. Situated just north of the huge wedge that extends north of Eta, ~40' NW of the star. Visually the cluster appears much smaller than the listed diameter of 20'. At 282x, the 12"x8" bipolar Homunculus nebula surrounding Eta Carina was an astounding sight. The orange central star appeared quasi-stellar with the unequal blowouts fairly prominent. They had an eerie, translucent appearance with the NW lobe somewhat smaller, fainter and more pinched with the SE lobe more circular. A possible dark lane is near the center and punctures the lobes. 12" (6/29/02 - Bargo, Australia): My first views of the Eta Carina nebula through Les Dalrymple's 12.5" and Gary's 20" were truly breathtaking and dwarfed the Orion Nebula in size and detail. The nebula is broken into 4 or 5 main separate masses of varying sizes, shapes and surface brightness by three wide, dark obscuring dust lanes. The mottled nebulosity has an amazing 3-dimensional curdled appearance and is riddled with dark bays and rifts. Outer loops and brighter streaks complete an amazing vista. The brightest section forms a triangular wedge isolated by prominent dark lane that cuts at a striking right angle. This wedge contains the centerpiece Eta Carina which has an amazing orange color. Extending from Eta are the two small lobes (one is brighter), referred to as the "Homunculus nebula" and appearing as an explosive event from the early 19th century in a HST image. Just preceding Eta is an elongated N-S, curving dark lane nicknamed the "Keyhole Nebula" by John Herschel, as well as the open cluster Tr 16 just south of Eta.