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 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.
Usually, a young star will ionize part of the same cloud from which it was born although only massive, hot stars can release sufficient energy to ionize a significant part of a cloud. In many emission nebulae, an entire cluster of young stars is doing the work.
The nebula's color depends on its chemical composition and degree of ionization. Due to the prevalence of hydrogen in interstellar gas, and its relatively low energy of ionization, many emission nebulae appear red due to the strong emissions of the Balmer series. If more energy is available, other elements will be ionized and green and blue nebulae become possible. By examining the spectra of nebulae, astronomers infer their chemical content. Most emission nebulae are about 90% hydrogen, with the remaining helium, oxygen, nitrogen, and other elements.
Some of the most prominent emission nebulae visible from the northern hemisphere are the North America Nebula (NGC 7000) and Veil Nebula NGC 6960/6992 in Cygnus, while in the south celestial hemisphere, the Lagoon Nebula M8 / NGC 6523 in Sagittarius and the Orion Nebula M42. Further in the southern hemisphere is the bright Carina Nebula NGC 3372.
Emission nebulae often have dark areas in them which result from clouds of dust which block the light.
IC 405 (also known as the Flaming Star Nebula, SH 2-229, or Caldwell 31) is an emission and reflection nebula in the constellation Auriga, surrounding the bluish star AE Aurigae. It shines at magnitude +6.0. Its celestial coordinates are RA 05h 16.2m dec +34° 28′. It surrounds the irregular variable star AE Aurigae and is located near the emission nebula IC 410, the open clusters M38 and M36, and the K-class star Iota Aurigae. The nebula measures approximately 37.0' x 19.0', and lies about 1,500 light-years away from Earth. It is believed that the proper motion of the central star can be traced back to the Orion's Belt area. The nebula is about 5 light-years across.List of diffuse nebulae
Reflection nebulaN11 (emission nebula)
N11 (also known as LMC N11, LHA 120-N 11) is the brightest emission nebula in the north-west part of the Large Magellanic Cloud in the Dorado constellation. The N11 complex is the second largest H II region of the Large Magellanic Cloud after the Tarantula Nebula. It covers an area of approximately 6 arc minutes across. It has an elliptical shape and consists of a large bubble surrounded by nine large nebulae. It was named by Karl Henize in 1956.When close-up, the nebula has pink clouds of glowing gas which resembles candy floss. It has been well studied over the years and extends 1,000 light-years across.Its particularly notable features include a huge cavity measuring 80 by 60 pc and a five million year old central cluster (NGC 1761). It is surrounded by several ionized clouds where young O stars are forming. Several massive stars are included within LMC-N11, including LH 9, LH 10, LH 13, LH 14. It includes a supernova remnant N11L. In the very centre of NGC 1761 is a bright multiple star HD 32228 which contains a rare blue Wolf-Rayet star, type WC5 or WC6, and an O-type bright giant.The brightest nebulosity within N11 is the northern region N11B (NGC 1763), also known as the Bean Nebula because of its shape. On the north-east edge of N11B is the more compact N11A, known as the Rose Nebula, which has rose-like petals of gas and dust and are illuminated due to the massive hot stars within its centre. It is also known as IC 2116 and was catalogued as a star HD 32340. The east side of the N11 complex is N11C (NGC 1769), an emission nebula containing at least two compact open clusters. Outside the main "bubble" of N11 to the northeast is N11E, also known as NGC 1773, a small bright nebula containing several massive young stars. The south portion of the bubble is N11F, also called NGC 1760. The western portion of the bubble is faint and poorly-defined.To the south-west of N11 is the 7th magnitude red giant HD 31754, a foreground object. Close to it is the open cluster NGC 1733. There are three more distant galaxies west of N11: the pair PGC 16243 and PGC 16244; and LEDA 89996. To the south of them lies NGC 1731 and TYC 8889-619-1 which are part of the LMC N4 complex. The bright globular cluster NGC 1783 lies to the north of N11.N44 (emission nebula)
N44 is an emission nebula with superbubble structure located in the Large Magellanic Cloud, a satellite galaxy of the Milky Way in the constellation Dorado. Originally catalogued in Karl Henize's "Catalogue of H-alpha emission stars and nebulae in the Magellanic Clouds" of 1956, it is approximately 1,000 light-years wide and 160,000-170,000 light-years distant. N44 has a smaller bubble structure inside known as N44F. The superbubble structure of N44 itself is shaped by the radiation pressure of a 40-star group located near its center; the stars are blue-white, very luminous, and incredibly powerful. N44F has been shaped in a similar manner; it has a hot, massive central star with an unusually powerful stellar wind that moves at 7 million kilometers per hour. This is because it loses material at 100 million times the rate of the Sun, or approximately 1,000,000,000,000,000 tons per year. However, varying density in the N44 nebula has caused the formation of several dust pillars that may conceal star formation. This variable density is likely caused by previous supernovae in the vicinity of N44; many of the stars that have shaped it will eventually also end as supernovae. The past effects of supernovae are also confirmed by the fact that N44 emits x-rays.N44 is classified as an emission nebula because it contains large regions of ionized hydrogen. However, the three strongest emission lines in the nebula are singly ionized oxygen atoms, which emit at an ultraviolet wavelength of 372.7 nm, doubly-ionized oxygen atoms, which emit at a blue-green wavelength of 500.7 nm, and neutral hydrogen atoms, which emit the hydrogen-alpha line at a red wavelength of 656.2 nm.NGC 1935
NGC 1935 (also known as ESO 56-EN110 and IC 2126) is an emission nebula which is part of the larger LMC-N44 nebula in the Dorado constellation. NGC 1935 is also located in the Large Magellanic Cloud. It was discovered by John Herschel in 1834 which was added to the Catalogue of Nebulae and Clusters of Stars as NGC 1935 and was observed by Williamina Fleming in 1901 and was later added to the Index Catalogue as IC 2126.NGC 2029
NGC 2029 (also known as ESO 56-EN156) is a emission nebula in the Dorado constellation and is part of the Large Magellanic Cloud. It is part of a complex of nebulae and stars, including NGC 2032, NGC 2035 and NGC 2040, It was discovered by James Dunlop on the 27 September 1826. Its apparent magnitude is 12.29, and its size is 2.25 arc minutes.The coordinates for NGC 2029 and NGC 2030 were reversed between Herschel's original Catalogue of Nebulae and Clusters of Stars and the New General Catalogue. NGC 2030, originally GC 2029, is an isolated nebula with an embedded star cluster, about 1.5 degrees north of NGC 2029.NGC 2074
NGC 2074 is a magnitude ~8 emission nebula in the Tarantula Nebula located in the constellation Dorado. It was discovered on 3 August 1826 by James Dunlop
and around 1835 by John Herschel. It is described as being "pretty bright, pretty large, much extended, [and having] 5 stars involved".NGC 2264
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.All of the objects are located in the Monoceros constellation and are located about 800 parsecs or 2600 light-years from Earth.
NGC 2264 is sometimes referred to as the Christmas Tree Cluster and the Cone Nebula. However, the designation of NGC 2264 in the New General Catalogue refers to both objects and not the cluster alone.
NGC2264 is the location where the Cone Nebula, The Stellar Snowflake Cluster and the Christmas Tree Cluster have formed in this emission nebula. For reference, the Stellar Snowflake Cluster is located 2,700 light years away in the constellation Monoceros. The Monoceros constellation is not typically visible by the naked eye due to its lack of colossal stars.
The Snowflake Cluster was granted its name due to its unmistakable pinwheel-like shape and its assortment of bright colors. The Christmas Tree star formation consists of young stars obscured by heavy layers of dust clouds. These dust clouds, along with hydrogen and helium are producing luminous new stars. The combination of dense clouds and an array of colors creates a color map filled with varying wavelengths. As seen in the photographs taken by the Spitzer Space telescope, we are able to differentiate between young, red stars and older blue stars.
With varying youthful stars, comes vast changes to the overall structure of the clusters and nebula. For a cluster to be considered a Snowflake, it must remain in the original location the star was formed.
When referring to this emission nebula overall, there are several aspects that contribute to the prominent configuration of a snowflake and/or Christmas tree cluster. There is a diverse arrangement of brilliant colors, and an evolving process of structure that follow star formation in a nebula.NGC 248
NGC 248 is an emission nebula in the Constellation Tucana. It was discovered in 1834 by the astronomer John Frederick William Herschel. NGC 248 is about 60 light-years long and 20 light-years wide
NGC 249 is an emission nebula in the constellation Tucana. It was discovered in 1826 by the astronomer James Dunlop.NGC 3199
NGC 3199 is a emission nebula in the constellation Carina. The object was discovered in 1826 by the Scottish astronomer James Dunlop. It is a bow shock around the central star, WR 18, a Wolf–Rayet star.NGC 592
NGC 592 is a H II region type emission nebula located in the Triangulum galaxy (M33) and thus in the constellation of Triangulum. The nebula contains an open cluster of stars and is approximately 2.86 million light-years away from Earth.NGC 6729
NGC 6729 is a reflection/emission nebula in the constellation Corona Australis. It was discovered by Johann Friedrich Julius Schmidt in 1861.This fan-shaped nebula opens from the star R Coronae Australis toward the star T CrA to the south-east. R CrA is a pre-main-sequence star in the Corona Australis molecular complex, one of the closer star-forming regions of the galaxy at a distance of 130 pc.N 180B
N 180B is an emission nebula located in the Large Magellanic Cloud.Pelican Nebula
The Pelican Nebula (also known as IC 5070 and IC 5067) is an H II region associated with the North America Nebula in the constellation Cygnus. The gaseous contortions of this emission nebula bear a resemblance to a pelican, giving rise to its name. The Pelican Nebula is located nearby first magnitude star Deneb, and is divided from its more prominent neighbour, the North America Nebula, by a molecular cloud filled with dark dust.
The Pelican is much studied because it has a particularly active mix of star formation and evolving gas clouds. The light from young energetic stars is slowly transforming cold gas to hot and causing an ionization front gradually to advance outward. Particularly dense filaments of cold gas are seen to still remain, and among these are found two jets emitted from the Herbig–Haro object 555. Millions of years from now this nebula might no longer be known as the Pelican, as the balance and placement of stars and gas will leave something that appears completely different.Reflection nebula
In astronomy, reflection nebulae are clouds of interstellar dust which might reflect the light of a nearby star or stars. The energy from the nearby stars is insufficient to ionize the gas of the nebula to create an emission nebula, but is enough to give sufficient scattering to make the dust visible. Thus, the frequency spectrum shown by reflection nebulae is similar to that of the illuminating stars. Among the microscopic particles responsible for the scattering are carbon compounds (e. g. diamond dust) and compounds of other elements such as iron and nickel. The latter two are often aligned with the galactic magnetic field and cause the scattered light to be slightly polarized.Sh2-101
Sharpless 101 (Sh2-101) is a H II region emission nebula located in the constellation Cygnus. It is sometimes also called the Tulip Nebula because it appears to resemble the outline of a tulip when imaged photographically. It was catalogued by astronomer Stewart Sharpless in his 1959 catalog of nebulae. It lies at a distance of about 6,000 light-years (5.7×1016 km; 3.5×1016 mi) from Earth.
Sh2-101, at least in the field seen from earth, is in close proximity to microquasar Cygnus X-1, site of one of the first suspected black holes. Cygnus X-1 is the bright star near the bottom right corner of the image presented here.Trifid Nebula
The Trifid Nebula (catalogued as Messier 20 or M20 and as NGC 6514) is an H II region located in Sagittarius. It was discovered by Charles Messier on June 5, 1764. Its name means 'divided into three lobes'. The object is an unusual combination of an open cluster of stars; an emission nebula (the lower, red portion), a reflection nebula (the upper, blue portion) and a dark nebula (the apparent 'gaps' within the emission nebula that cause the trifurcated appearance; these are also designated Barnard 85). Viewed through a small telescope, the Trifid Nebula is a bright and peculiar object, and is thus a perennial favorite of amateur astronomers.The Trifid Nebula is a star-forming region in the Scutum spiral arm of the Milky Way.
The most massive star that has formed in this region is HD 164492A, an O7.5III star with a mass more than 20 times the mass of the Sun.
This star is surrounded by a cluster of approximately 3100 young stars.Westerhout 5
Westerhout 5 (Sharpless 2-199, LBN 667, Soul Nebula) is an emission nebula located in Cassiopeia. Several small open clusters are embedded in the nebula: CR 34, 632, and 634 (in the head) and IC 1848 (in the body). The object is more commonly called by the cluster designation IC 1848.
Small emission nebula IC 1871 is present just left of the top of the head, and small emission nebulae 670 and 669 are just below the lower back area.
The galaxies Maffei 1 and Maffei 2 are both nearby the nebula, although light extinction from the Milky Way makes them very hard to see.
Once thought to be part of the Local Group, they are now known to belong to their own group- the IC 342/Maffei Group.
This complex is the eastern neighbor of IC1805 (Heart Nebula) and the two are often mentioned together as the "Heart and Soul".