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.

Nicolas-Louis de Lacaille discovered (telescopically) NGC 3372 = Lac III-6 = D 309 = h3295 in 1751-1752 with a 1/2-inch telescope at 8x during his expedition to the Cape of Good Hope. He recorded a "Large group of a great number of small stars, little compressed, and filling out the space of a kind of a semi-circle of 15 to 20 minutes in diameter; with a slight nebulosity spreading in that space." Of course, the nebula and embedded clusters is a prominent naked-eye object, so was certainly known by southern sky watchers.

James Dunlop observed it at least 13 times and recorded "(Eta Roboris Caroli, Bode) is a bright star of the 3rd magnitude, surrounded by a multitude of small stars, and pretty strong nebulosity; very similar in its nature to that in Orion, but not so bright... I can count twelve or fourteen extremely minute stars surrounding Eta in the space of about 1'; several of them appear close to the disk: there is a pretty bright small star about the 10th magnitude N.f. the Eta, and distant about 1'. The nebulosity is pretty strongly marked; that on the south side is very unequal in brightness, and the different portions of the nebulosity are completely detached, as represented in the figure [plate III, figure 14]. There is much nebulosity in this place, and very much extensive nebulosity throughout the Robur Caroli, which is also very rich in small stars."

John Herschel commented "It is not easy for language to convey a full impression of the beauty and sublimity of the spectacle which this nebula offers, as it enters the field of the telescope fixed in R. A., by the diurnal motion, ushered in as it is by so glorious and innumerable a procession of stars, to which it forms a sort of climax, and in a part of the heavens otherwise full of interest."

During a 5-year period in the 1840's and '50s Eta Car brightened from 1.5 to -1 (chronicled by John Herschel) and was temporarily the second brightest star in the sky, nearly rivaling Sirius. This outburst later created the double-lobed Homunculus Nebula, discovered in 1944. According to Wolfgang Steinicke, in 1863, Francis Abbott, an amateur in Tasmania, claimed a decrease in the size and brightness of the main nebula and displacement relative to Eta Car using a 4-inch refractor, but a number of critical replies followed by Lt. John Herschel (son of JH), Airy and Lassell. Interestingly, the dark "Keyhole Nebula" does appear to have lost contrast based on JH's sketches and descriptions.

As far as the origin of the nickname "Keyhole Nebula" it's generally assumed that JH coined the phrase and his sketch of the elongated dark patch near Eta certainly appears like a perfect classic "keyhole". But a search through his Cape Observations and articles about the brightening of Eta Car and possible variability of the nebula reveals he used the term "lemniscate" to describe the shape (must have been his early mathematical training).

In an 1873 issue of Appletons' Journal, Emma Converse, who reported on astronomical topics for the popular press, summarizes the dispute about changes in the nebula in an article titled "Eta Argus". She mentions "In the middle of the brightest part of the nebulous light there was a dark vacancy, of a form resembling a keyhole, or the geometrical figure called a lemniscate, around which the light of the nebula was not uniform." Later she mentions "The southern loop of Herschel's lemniscate, or keyhole-shaped cavity had bulged out into the vacuity, forming an isthmus that trended north-south." Agnes Mary Clerke refers to the "Key-Hole Nebula" in her "The System of the Stars" (second edition, 1905), plate XVII taken with the Bruce 24-inch at Arequipa in 1896.

300/350mm - 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.

400/500mm - 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.

600/800mm - 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".

Notes by Steve Gottlieb