An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star. Among the several different types of emission nebulae are H II regions, in which star formation is taking place and young, massive stars are the source of the ionizing photons; and planetary nebulae, in which a dying star has thrown off its outer layers, with the exposed hot core then ionizing them.
The Orion Nebula is a diffuse nebula situated in the Milky Way, being south of Orion's Belt in the constellation of Orion. It is one of the brightest nebulae and is visible to the naked eye in the night sky with apparent magnitude 4.0. It is 1,344 ± 20 light-years (412.1 ± 6.1 pc) away and is the closest region of massive star formation to Earth. The M42 nebula is estimated to be 24 light-years across. It has a mass of about 2,000 times that of the Sun. Older texts frequently refer to the Orion Nebula as the Great Nebula in Orion or the Great Orion Nebula.
NGC 2264 is the designation number of the New General Catalogue that identifies two astronomical objects as a single object: the Cone Nebula, and the Christmas Tree Cluster. Two other objects are within this designation but not officially included, the Snowflake Cluster, and the Fox Fur Nebula.
The Trifid Nebula is an H II region in the north-west of Sagittarius in a star-forming region in the Milky Way's Scutum-Centaurus Arm. It was discovered by Charles Messier on June 5, 1764. Its name means 'three-lobe'. The object is an unusual combination of an open cluster of stars, an emission nebula, a reflection nebula, and a dark nebula. Viewed through a small telescope, the Trifid Nebula is a bright and peculiar object, and is thus a perennial favorite of amateur astronomers.
The Lagoon Nebula is a giant interstellar cloud in the constellation Sagittarius. It is classified as an emission nebula and as an H II region.
Messier 78 or M78, also known as NGC 2068, is a reflection nebula in the constellation Orion. It was discovered by Pierre Méchain in 1780 and included by Charles Messier in his catalog of comet-like objects that same year.
Open Cluster NGC 2175 is an open cluster in the Orion constellation, embedded in a diffusion nebula. It was discovered by Giovanni Batista Hodierna before 1654 and independently discovered by Karl Christian Bruhns in 1857. NGC 2175 is at a distance of about 6,350 light years away from Earth.
Sh2-279 is an HII region and bright nebulae that includes a reflection nebula located in the constellation Orion. It is the northernmost part of the asterism known as Orion's Sword, lying 0.6° north of the Orion Nebula. The reflection nebula embedded in Sh2-279 is popularly known as the Running Man Nebula.
NGC 7380 is a young open cluster of stars in the northern circumpolar constellation of Cepheus, discovered by Caroline Herschel in 1787. The surrounding emission nebulosity is known colloquially as the Wizard Nebula, which spans an angle of 25′. German-born astronomer William Herschel included his sister's discovery in his catalog, and labelled it H VIII.77. The nebula is known as S 142 in the 1959 Sharpless catalog (Sh2-142). It is extremely difficult to observe visually, usually requiring very dark skies and an O-III filter. The NGC 7380 complex is located at a distance of approximately 8.5 kilolight-years from the Sun, in the Perseus Arm of the Milky Way.
NGC 6334, colloquially known as the Cat's Paw Nebula, Bear Claw Nebula, or Gum 64, is an emission nebula and star-forming region located in the constellation Scorpius. NGC 6334 was discovered by astronomer John Herschel in 1837, who observed it from the Cape of Good Hope in South Africa. The nebula is located in the Carina–Sagittarius Arm of the Milky Way, at a distance of approximately 5.5 kilolight-years from the Sun.
NGC 1555, sometimes known as Hind's Variable Nebula, is a variable nebula, illuminated by the star T Tauri, located in the constellation Taurus. It is also in the second Sharpless catalog as 238. It is a Herbig–Haro object. The nebula was discovered on October 11, 1852, by John Russell Hind.
NGC 2359 is an emission nebula in the constellation Canis Major. The nebula is approximately 3,670 parsecs away and 30 light-years in size. The central star is the Wolf-Rayet star WR7, an extremely hot star thought to be in a brief pre-supernova stage of evolution. It is similar in nature to the Bubble Nebula, but interactions with a nearby large molecular cloud are thought to have contributed to the more complex shape and curved bow-shock structure of Thor's Helmet.
NGC 6820 is a small reflection nebula near the open cluster NGC 6823 in Vulpecula. The reflection nebula and cluster are embedded in a large faint emission nebula called Sh 2-86. The whole area of nebulosity is often referred to as NGC 6820.
NGC 7822 is a young star forming complex in the constellation of Cepheus. The complex encompasses the emission region designated Sharpless 171, and the young cluster of stars named Berkeley 59. The complex is believed to be some 800–1000 pc distant, with the younger components aged no more than a few million years. The complex also includes one of the hottest stars discovered within 1 kpc of the Sun, namely BD+66 1673, which is an eclipsing binary system consisting of an O5V that exhibits a surface temperature of nearly 45,000 K and a luminosity about 100,000 times that of the Sun. The star is one of the primary sources illuminating the nebula and shaping the complex's famed pillars of creation-type formations, the elephant trunks.
Sh2-54 is an extended bright nebula in the constellation of Serpens.
The Ghost Nebula is a reflection nebula located in the constellation Cepheus.
NGC 1929 is an open cluster associated with the emission nebula located within the N44 nebula in the Dorado constellation and part of the Large Magellanic Cloud. It was discovered by James Dunlop on August 3 1826. Its apparent magnitude is 14.0, and its size is 0.8 arc minutes.
NGC 1624, also known as Sh2-212 in the Sharpless catalog, is a very young open cluster in the constellation Perseus inside an emission nebula. It was discovered by German-British astronomer William Herschel in 1790. NGC 1624 is about 20,000 ly from Earth, and latest estimates give it an age of less than 4 million years. Its apparent magnitude is 11.8, and apparent diameter is about 3.0 arc minutes. Its celestial location is right ascension (α) 04h 40m 36.0s and declination (δ) +50° 27′ 42″. It is potentially an area of massive star formation.
NGC 3312 is a large and highly inclined spiral galaxy located about 194 million light-years away in the constellation Hydra. The galaxy was discovered by astronomer John Herschel on March 26, 1835. It was later rediscovered by astronomer Guillaume Bigourdan on February 26, 1887. NGC 3312 was later listed and equated with IC 629 because the two objects share essentially the same celestial coordinates. NGC 3312 is the largest spiral galaxy in the Hydra Cluster and is also classified as a LINER galaxy.
