An Etymological Dictionary of Astronomy and Astrophysics
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A dark cloud of dust and gas that absorbs light from and impedes the view of background stars; dark nebula.

→ absorption; → nebula.

An interstellar cloud of ionized gas with two main lobes which lie symmetrically on either side of a central star. The bipolar shape is generally due to the ejection of material by the central star in opposing directions.

→ bipolar; → nebula.

A → nebula displaying two nearly symmetric lobes of matter that are being ejected from a central star at a speed of about 600,000 km per hour (each lobe nearly one light-year in length). The Boomerang Nebula resides 5,000 → light-years from Earth in the direction of the Southern constellation → Centaurus.

Boomerang, adapted from wo-mur-rang, boo-mer-rit, in the language of Australian aborigines; → nebula.

A → planetary nebula which is thought to have experienced a → very late thermal pulse (VLTP) when the central star (→ CSPN) was on the → white dwarf cooling track. The VLTP event occurs when the thermonuclear → hydrogen shell burning has built up a → shell of helium with the critical mass to ignite its → fusion into carbon and oxygen (→ helium shell burning). Since the → white dwarf envelope is shallow, the increase of pressure from this last helium shell flash leads to the ejection of newly processed material inside the old planetary nebula, leaving the stellar core intact. As the stellar envelope expands, its → effective temperature decreases and the star goes back to the → asymptotic giant branch (AGB) region in the → H-R diagram. The subsequent stellar evolution is fast and will return the star back to the → Post-AGB track in the H-R diagram: the envelope of the star contracts, its effective temperature and ionizing photon flux increase, and a new fast stellar wind develops (see, e.g. J. A. Toalá et al. 2015, ApJ 799, 67).

→ born; → again; → planetary; → nebula.

In contrast to a → dark nebula, a bright cloud of interstellar gas and dust. The term designates both emission nebulae and reflection nebulae.

→ bright; → nebula.

The → diffuse nebula NGC 7635 in the constellation → Cassiopeia lying at a distance of about 11,000 light-years. About 10 light-years across, it is visible with a small telescope.

→ bubble; → nebula.

The double-lobed → planetary nebula NGC 6302, which lies in → Scorpius at a distance of about 4000 → light-years. The central very hot star seems to have violently ejected material in two distinct directions.

→ bug; → nebula.

Šâparak "night butterfly, bat," from šab "night" + parak "flying," from paridan "to fly."

A → bipolar nebula and → OH/IR source with technical designation OH 231.8+4.2. It is a → proto-planetary nebula (PPN) 1.4 → light-years long and located some 5,000 light-years from Earth in the constellation → Puppis. The obscured → central star, named QX Pup, is classified as M9-10 III and has a → Mira-like variability consistent with an evolved → asymptotic giant branch (AGB) star. The late evolution of this object may have been complex since it has a binary → companion star (of type A0 V) that has been indirectly identified from analysis of the spectrum of the hidden central source reflected by the nebular dust. The system has a total luminosity of ~ 10⁴ Lsun and its systemic velocity relative to the → Local Standard of Rest is V_LSR ~ 34 km s^-1. OH 231.8+4.2 is very likely a member of the → open cluster M46 with a progenitor mass of ~ 3 Msun. The nebula is also known as the Rotten Egg Nebula because it contains a lot of sulphur, an element that, when combined with other elements, smells like a rotten egg (see, e.g., Prieto et al., 2015, A&A, 575, A84).

The name "Calabash Nebula" was first proposed by Icke & Preston, 1989, A&A, 211, 409. It refers to the apparent form of the object which resembles a calabash "a tree that has large, rounded gourdlike fruit; the fruit of any of these plants," from Sp. calabaza, possibly from Ar. qar'ah yâbisah "dry gourd," from Pers. kharabuz, used of various large melons; → nebula.

One of the most prominent → massive star formation regions of the → Milky Way, also known as NGC 3372. It is associated with a giant → H II region of the same name, which spans about 4 square degrees on the sky and is split by a remarkable V-shaped → dust lane. The Carina Nebula harbors several → star clusters, mainly → Trumpler 14, → Trumpler 16, and Collinder 228, including more than 60 known → O-type stars in addition to the extreme → LBV star → Eta Carinae. This gas and dust complex is associated with a → giant molecular cloud extending over about 130 pc. Large cavities within the molecular cloud are supposed to be carved out by the massive star clusters. There are also several → Herbig-Haro objects and → bipolar outflows.

→ Carina; → nebula.

An emission nebula located about 3,000 light-years away toward the → constellation  → Cygnus. It is thought to be a region of active → star formation.

Cocoon, from Provençal Fr. coucoun, from O.Fr. coque "egg shell, nut shell," L. coccum "berry," from Gk. kokkos "berry, seed;" → star; → nebula.

Miq, → nebula; pilé "the silkworm's cocoon; a purse", cf. Skt. patta- "woven silk."

A star whose spectrum shows striking similarities to → B[e] stars and is evolving into a → planetary nebula (→ preplanetary nebula).

→ compact; → planetary; → nebula; → B[e] star.

An expanding cloud of debris from the explosion of a → Type I supernova in the → constellation  → Taurus. Its light reached Earth in 1054 and was visible to the naked eye even in the daytime. Lying about 6,300 → light-years away, the Crab nebula is an intense → radio source (Tau A), and also a source of X-rays and gamma-rays. The diameter of the → supernova remnant is about 6 light-years; it is expanding at velocity of 1000 km/sec.

→ crab; → nebula.

An interstellar cloud of absorbing matter whose dust particles obscure the light from stars beyond it and give the cloud the appearance of a dark, starless region.

→ dark; → nebula.

An irregularly shaped and low density interstellar cloud visible in the optical wavelengths.

→ diffuse; → nebula.

One of the brightest planetary nebulae; it lies in the constellation → Vulpecula at a distance of about 1000 light-years. It was discovered by Charles Messier in 1764.

Dumbbell "a short bar with weights at each end that is used for exercise," from dumb + bell. When viewed in a small telescope, the brighter portion of the nebula shows like a bipolar geometry, hence the name; → nebula.

Dambel loanword from dumbbell, as above; → nebula.

A prominent → H II region in the constellation → Serpens lying about 2 kpc away from the Sun. It measures about 30' across and surrounds the open cluster → M16 (NGC 6611), which contains at least 20 stars of spectral type B0.5 or earlier, including one 05V. At a projected distance from the cluster of about 2 pc, where the H II region has expanded into surrounding → molecular cloud, a striking → elephant trunk morphology or → pillar results. The nebula is the site of ongoing → star formation, especially in these pillar structures. The Eagle Nebula is often erroneously given the cluster's designation (M16).

Eagle, because the nebula's shape is vaguely reminiscent of an eagle in flight; from M.E. egle, from O.Fr. egle, from O.Prov. aigla, from L. → aquila "black eagle;" → nebula.

Miq, → nebula; Šâhin, → aquila.

An elongated dark structure of gas and dust in the → H II region IC 1396. It spans about 5 degrees on the sky in the constellation → Cepheus, about 2400 → light-years from the Earth. The Elephant Trunk Nebula is believed to be site of star formation, containing several very young stars. It is an example of → elephant trunks associated with star forming regions.

→ elephant trunk; → nebula.

An ionized nebula whose spectrum consists of → emission lines. → planetary nebula; → H II region.

→ emission; → nebula.

A nebula, generally ionized, consisting of filament-like structures of gas, such as the Veil Nebula (NGC 6960) or the supernova remnant IC 443.

Filamentary adj. of → filament; → nebula.

An → H II region, a → planetary nebula, or a → supernova remnant.

→ gaseous; → nebula.