The Caldwell catalogue is an astronomical catalogue of 109 star clusters, nebulae, and galaxies for observation by amateur astronomers. The list was compiled by Patrick Moore as a complement to the Messier catalogue.
While the Messier catalogue is used by amateur astronomers as a list of deep-sky objects for observation, Moore noted that Messier's list was not compiled for that purpose and excluded many of the sky's brightest deep-sky objects, such as the Hyades, the Double Cluster (NGC 869 and NGC 884), and the Sculptor Galaxy (NGC 253). The Messier catalogue was actually compiled as a list of known objects that might be confused with comets. Moore also observed that since Messier compiled his list from observations in Paris, it did not include bright deep-sky objects visible in the Southern Hemisphere, such as Omega Centauri, Centaurus A, the Jewel Box, and 47 Tucanae. Moore compiled a list of 109 objects to match the commonly accepted number of Messier objects (he excluded M110), and the list was published in Sky & Telescope in December 1995.
Moore used his other surname – Caldwell – to name the list, since the initial of "Moore" is already used for the Messier catalogue. Entries in the catalogue are designated with a "C" and the catalogue number (1 to 109).
Unlike objects in the Messier catalogue, which are listed roughly in the order of discovery by Messier and his colleagues, the Caldwell catalogue is ordered by declination, with C1 being the most northerly and C109 being the most southerly, although two objects (NGC 4244 and the Hyades) are listed out of sequence. Other errors in the original list have since been corrected: it incorrectly identified the S Norma Cluster (NGC 6087) as NGC 6067 and incorrectly labelled the Lambda Centauri Cluster (IC 2944) as the Gamma Centauri Cluster.
Montage of Caldwell Catalogue objects.
|Star clusters and nebulae||6|
|Caldwell number||NGC number||Common name||Picture||Type||Distance
|C1||NGC 188||Open Cluster||4.8||Cepheus||8.1|
|C2||NGC 40||Bow-Tie Nebula||Planetary Nebula||3.5||Cepheus||11|
|C3||NGC 4236||Barred Spiral Galaxy||7,000||Draco||9.7|
|C4||NGC 7023||Iris Nebula||Open Cluster and Nebula||1.4||Cepheus||7|
|C5||IC 342||Spiral Galaxy||10,000||Camelopardalis||9|
|C6||NGC 6543||Cat's Eye Nebula||Planetary Nebula||3||Draco||9|
|C7||NGC 2403||Spiral Galaxy||14,000||Camelopardalis||8.4|
|C8||NGC 559||Open Cluster||3.7||Cassiopeia||9.5|
|C10||NGC 663||Open Cluster||7.2||Cassiopeia||7.1|
|C11||NGC 7635||Bubble Nebula||Nebula||7.1||Cassiopeia||-|
|C12||NGC 6946||Fireworks Galaxy||Spiral Galaxy||18,000||Cepheus||8.9|
|C13||NGC 457||Owl Cluster, E.T. Cluster||Open Cluster||-||Cassiopeia||6.4|
|C14||NGC 869 & NGC 884||Double Cluster, H & χ Persei||Open Cluster||7.3||Perseus||4|
|C15||NGC 6826||Blinking Planetary||Planetary Nebula||2.2||Cygnus||10|
|C16||NGC 7243||Open Cluster||2.5||Lacerta||6.4|
|C17||NGC 147||Dwarf Spheroidal Galaxy||2,300||Cassiopeia||9.3|
|C18||NGC 185||Dwarf Spheroidal Galaxy||2,300||Cassiopeia||9.2|
|C19||IC 5146||Cocoon Nebula||Open Cluster and Nebula||3.3||Cygnus||7.2|
|C20||NGC 7000||North America Nebula||Nebula||1.8||Cygnus||4|
|C21||NGC 4449||Irregular galaxy||10,000||Canes Venatici||9.4|
|C22||NGC 7662||Blue Snowball||Planetary Nebula||3.2||Andromeda||9|
|C23||NGC 891||Spiral Galaxy||31,000||Andromeda||10|
|C24||NGC 1275||Perseus A||Type-cD galaxy||230,000||Perseus||11.6|
|C25||NGC 2419||Globular Cluster||275||Lynx||10.4|
|C26||NGC 4244||Spiral Galaxy||10,000||Canes Venatici||10.2|
|C27||NGC 6888||Crescent Nebula||Nebula||4.7||Cygnus||7.4|
|C28||NGC 752||Open Cluster||1.2||Andromeda||5.7|
|C29||NGC 5005||Spiral Galaxy||69,000||Canes Venatici||9.8|
|C30||NGC 7331||Spiral Galaxy||47,000||Pegasus||9.5|
|C31||IC 405||Flaming Star Nebula||Nebula||1.6||Auriga||-|
|C32||NGC 4631||Whale Galaxy||Barred Spiral Galaxy||22,000||Canes Venatici||9.3|
|C33||NGC 6992||East Veil Nebula||Supernova Remnant||2.5||Cygnus||-|
|C34||NGC 6960||West Veil Nebula||Supernova Remnant||2.5||Cygnus||-|
|C35||NGC 4889||Type-cD galaxy||300,000||Coma Berenices||11.4|
|C36||NGC 4559||Spiral Galaxy||32,000||Coma Berenices||9.9|
|C37||NGC 6885||Open Cluster||1.95||Vulpecula||6|
|C38||NGC 4565||Needle Galaxy||Spiral Galaxy||32,000||Coma Berenices||9.6|
|C39||NGC 2392||Eskimo Nebula/Clown Face Nebula||Planetary Nebula||4||Gemini||10|
|C40||NGC 3626||Spiral Galaxy||86,000||Leo||10.9|
|C41||Mel 25||Hyades||Open Cluster||0.151||Taurus||0.5|
|C42||NGC 7006||Globular Cluster||135||Delphinus||10.6|
|C43||NGC 7814||Spiral Galaxy||49,000||Pegasus||10.5|
|C44||NGC 7479||Barred Spiral Galaxy||106,000||Pegasus||11|
|C45||NGC 5248||Spiral Galaxy||74,000||Boötes||10.2|
|C46||NGC 2261||Hubble's Variable Nebula||Nebula||2.5||Monoceros||-|
|C47||NGC 6934||Globular Cluster||57||Delphinus||8.9|
|C48||NGC 2775||Spiral Galaxy||55,000||Cancer||10.3|
|C49||NGC 2237||Rosette Nebula||Nebula||4.9||Monoceros||9.0|
|C50||NGC 2244||Open Cluster||4.9||Monoceros||4.8|
|C51||IC 1613||Irregular galaxy||2,300||Cetus||9.3|
|C52||NGC 4697||Elliptical galaxy||76,000||Virgo||9.3|
|C53||NGC 3115||Spindle Galaxy||Lenticular Galaxy||22,000||Sextans||9.2|
|C54||NGC 2506||Open Cluster||10||Monoceros||7.6|
|C55||NGC 7009||Saturn Nebula||Planetary Nebula||1.4||Aquarius||8|
|C56||NGC 246||Planetary Nebula||1.6||Cetus||8|
|C57||NGC 6822||Barnard's Galaxy||Barred irregular galaxy||2,300||Sagittarius||9|
|C58||NGC 2360||Open Cluster||3.7||Canis Major||7.2|
|C59||NGC 3242||Ghost of Jupiter||Planetary Nebula||1.4||Hydra||9|
|C60||NGC 4038||Antennae Galaxies||Galaxy||83,000||Corvus||10.7|
|C61||NGC 4039||Antennae Galaxies||Interacting galaxy||83,000||Corvus||13|
|C62||NGC 247||Spiral Galaxy||6,800||Cetus||8.9|
|C63||NGC 7293||Helix Nebula||Planetary Nebula||0.522||Aquarius||7.3|
|C64||NGC 2362||Open Cluster and Nebula||5.1||Canis Major||4.1|
|C65||NGC 253||Sculptor Galaxy||Galaxy||9,800||Sculptor||7.1|
|C66||NGC 5694||Globular Cluster||113||Hydra||10.2|
|C68||NGC 6729||R CrA Nebula||Nebula||0.424||Corona Australis||-|
|C69||NGC 6302||Bug Nebula||Planetary Nebula||5.2||Scorpius||13|
|C71||NGC 2477||Open Cluster||3.7||Puppis||5.8|
|C73||NGC 1851||Globular Cluster||39.4||Columba||7.3|
|C74||NGC 3132||Eight Burst Nebula||Planetary Nebula||2||Vela||8|
|C75||NGC 6124||Open Cluster||1.5||Scorpius||5.8|
|C76||NGC 6231||Open Cluster and Nebula||6||Scorpius||2.6|
|C77||NGC 5128||Centaurus A||Galaxy||16,000||Centaurus||7|
|C78||NGC 6541||Globular Cluster||22.3||Corona Australis||6.6|
|C79||NGC 3201||Globular Cluster||17||Vela||6.8|
|C80||NGC 5139||Omega Centauri||Globular Cluster||17.3||Centaurus||3.7|
|C81||NGC 6352||Globular Cluster||18.6||Ara||8.2|
|C82||NGC 6193||Open Cluster||4.3||Ara||5.2|
|C84||NGC 5286||Globular Cluster||36||Centaurus||7.6|
|C85||IC 2391||Omicron Velorum Cluster||Open Cluster||0.5||Vela||2.5|
|C86||NGC 6397||Globular Cluster||7.5||Ara||5.7|
|C87||NGC 1261||Globular Cluster||55.5||Horologium||8.4|
|C88||NGC 5823||Open Cluster||3.4||Circinus||7.9|
|C89||NGC 6087[note 1]||S Norma Cluster||Open Cluster||3.3||Norma||5.4|
|C90||NGC 2867||Planetary Nebula||5.5||Carina||10|
|C91||NGC 3532||Wishing Well Cluster||Open Cluster||1.6||Carina||3|
|C92||NGC 3372||Eta Carinae Nebula||Nebula||7.5||Carina||3|
|C93||NGC 6752||Globular Cluster||13||Pavo||5.4|
|C94||NGC 4755||Jewel Box||Open Cluster||4.9||Crux||4.2|
|C95||NGC 6025||Open Cluster||2.5||Triangulum Australe||5.1|
|C96||NGC 2516||Open Cluster||1.3||Carina||3.8|
|C97||NGC 3766||Pearl Cluster||Open Cluster||5.8||Centaurus||5.3|
|C98||NGC 4609||Open Cluster||4.2||Crux||6.9|
|C99||-||Coalsack Nebula||Dark Nebula||0.61||Crux||-|
|C100||IC 2944||Lambda Centauri Nebula||Open Cluster and Nebula||6||Centaurus||4.5|
|C102||IC 2602||Theta Car Cluster||Open Cluster||0.492||Carina||1.9|
|C103||NGC 2070||Tarantula Nebula||Open Cluster and Nebula||170||Dorado||8.2|
|C104||NGC 362||Globular Cluster||27.7||Tucana||6.6|
|C105||NGC 4833||Globular Cluster||19.6||Musca||7.4|
|C106||NGC 104||47 Tucanae||Globular Cluster||14.7||Tucana||4|
|C107||NGC 6101||Globular Cluster||49.9||Apus||9.3|
|C108||NGC 4372||Globular Cluster||18.9||Musca||7.8|
|C109||NGC 3195||Planetary Nebula||5.4||Chamaeleon||11.6|
|Caldwell number||NGC number||Common name||Picture||Object type||Distance to object in thousands of light years||Constellation||Apparent magnitude|
An astronomical catalog or catalogue is a list or tabulation of astronomical objects, typically grouped together because they share a common type, morphology, origin, means of detection, or method of discovery. Astronomical catalogs are usually the result of an astronomical survey of some kind.C56
C56 or C-56 may refer to :
C-56 Lodestar, an American military aircraft
C-56 (Michigan county highway)
JNR Class C56, a class of Japanese steam locomotive
Caldwell 56 (NGC 246, the Skull Nebula), a planetary nebula in the constellation Cetus
Sickness Insurance (Sea) Convention, 1936 code
Two Knights Defense ECO code
Planetary nebula referenced as C56 in Caldwell catalogue
Ovarian cancer ICD-10 code
Hexachlorocyclopentadiene, an organochlorine compound that is a precursor to several pesticidesRelated:
S56 (disambiguation) (example: the S56, a Soviet submarine labeled C-56 using Cyrillic alphabet)C58
C58 or C-58 may refer to :
C-58 Bolo, an American military aircraft
C-58 (Michigan county highway)
JNR Class C58, a class of Japanese steam locomotive
HMS Fiji (C58), a 1940 British Royal Navy cruiser
Caldwell 58 (NGC 2360), an open cluster in the constellation Canis Majorand also :
Two Knights Defense ECO code
NGC 2360 referenced C58 in Caldwell catalogue
Minimum Age (Sea) Convention (Revised), 1936 code
a Toyota C transmission
Choriocarcinoma ICD-10 codeC89
C89 may refer to:
C89 (C version) or ANSI C, a C programming-language version
Ruy Lopez (ECO code: C60–C99), a chess opening
KNHC, a radio station in Seattle, Washington known as C89.5
Night Work (Women) Convention (Revised), 1948, an ILO convention
NGC 6087 (Caldwell catalogue: C89), an open clusters in the constellation Norma
Sylvania Airport, an airport in Wisconsin with the FAA LID "C89"Charles Messier
Charles Messier (French: [me.sje]; 26 June 1730 – 12 April 1817) was a French astronomer most notable for publishing an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the Messier objects. The purpose of the catalogue was to help astronomical observers, in particular comet hunters like himself, distinguish between permanent and transient visually diffuse objects in the sky.Coalsack Nebula
The Coalsack Nebula (Southern Coalsack, or simply the Coalsack) is the most prominent dark nebula in the skies, being easily visible to the naked eye as a dark patch silhouetted against the southern Milky Way. It is located at a distance of approximately 600 light-years away from Earth, in the constellation Crux.Double Cluster
The Double Cluster (also known as Caldwell 14) is the common name for the open clusters NGC 869 and NGC 884 (often designated h Persei and χ Persei, respectively), which are close together in the constellation Perseus. Both visible with the naked eye, NGC 869 and NGC 884 lie at a distance of 7500 light years. NGC 869 has a mass of 3700 solar masses and NGC 884 weighs in at 2800 solar masses; however, later research has shown both clusters are surrounded with a very extensive halo of stars, with a total mass for the complex of at least 20,000 solar masses. Based on their individual stars, the clusters are relatively young, both 12.8 million years old. In comparison, the Pleiades have an estimated age ranging from 75 million years to 150 million years. There are more than 300 blue-white super-giant stars in each of the clusters. The clusters are also blueshifted, with NGC 869 approaching Earth at a speed of 39 km/s (24 mi/s) and NGC 884 approaching at a similar speed of 38 km/s (24 mi/s). Their hottest main sequence stars are of spectral type B0.Herschel 400 Catalogue
The Herschel 400 catalogue is a subset of William Herschel's original Catalogue of Nebulae and Clusters of Stars, selected by Brenda F. Guzman (Branchett), Lydel Guzman, Paul Jones, James Morrison, Peggy Taylor and Sara Saey of the Ancient City Astronomy Club in St. Augustine, Florida, United States c. 1980. They decided to generate the list after reading a letter published in Sky & Telescope by James Mullaney of Pittsburgh, Pennsylvania, USA.In this letter Mr. Mullaney suggested that William Herschel's original catalogue of 2,500 objects would be an excellent basis for deep sky object selection for amateur astronomers looking for a challenge after completing the Messier Catalogue.
The Herschel 400 is a subset of John Herschel's General Catalogue of Nebulae and Clusters published in 1864 of 5,000 objects, and hence also of the New General Catalogue.
The catalogue forms the basis of the Astronomical League's Herschel 400 club. In 1997, another subset of 400 Herschel objects was selected by the Rose City Astronomers of Portland, Oregon as the Herschel II list, which forms the basis of the Astronomical League's Herschel II Program.Messier object
The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his "Catalogue des Nébuleuses et des Amas d'Étoiles" ("Catalogue of Nebulae and Star Clusters").
Because Messier was interested in finding only comets, he created a list of non-comet objects that frustrated his hunt for them. The compilation of this list, in collaboration with his assistant Pierre Méchain, is known as the Messier catalogue. This catalogue of objects is one of the most famous lists of astronomical objects, and many Messier objects are still referenced by their Messier number.
The catalogue includes some astronomical objects that can be observed from Earth’s Northern Hemisphere such as deep-sky objects, a characteristic which makes the Messier objects extremely popular targets for amateur astronomers.A preliminary version first appeared in Memoirs of the French Academy of Sciences in 1771,
and the last item was added in 1966 by Kenneth Glyn Jones, based on Messier's observations.
The first version of Messier's catalogue contained 45 objects and was published in 1774 in the journal of the French Academy of Sciences in Paris. In addition to his own discoveries, this version included objects previously observed by other astronomers, with only 17 of the 45 objects being Messier’s.
By 1780 the catalogue had increased to 80 objects. The final version of the catalogue containing 103 objects was published in 1781 in the Connaissance des Temps for the year 1784.
However, due to what was thought for a long time to be the incorrect addition of Messier 102, the total number remained 102. Other astronomers, using side notes in Messier's texts, eventually filled out the list up to 110 objects.The catalogue consists of a diverse range of astronomical objects, ranging from star clusters, nebula to galaxies. For example, Messier 1 is a supernova remnant, known as the Crab Nebula, and the great spiral Andromeda Galaxy is M31. Many further inclusions followed in the next century when the first addition came from Nicolas Camille Flammarion in 1921, who added Messier 104 after finding Messier’s side note in his 1781 edition exemplar of the catalogue. M105 to M107 were added by Helen Sawyer Hogg in 1947, M108 and M109 by Owen Gingerich in 1960, and M110 by Kenneth Glyn Jones in 1967.NGC 4889
NGC 4889 (also known as Coma B) is an E4 supergiant elliptical galaxy. It was discovered in 1785 by the British astronomer Frederick William Herschel I, who catalogued it as a bright, nebulous patch. The brightest galaxy within the northern Coma Cluster, it is located at a median distance of 94 million parsecs (308 million light years) from Earth. At the core of the galaxy is a supermassive black hole that heats the intracluster medium through the action of friction from infalling gases and dust. The gamma ray bursts from the galaxy extend out to several million light years of the cluster.
As with other similar elliptical galaxies, only a fraction of the mass of NGC 4889 is in the form of stars. They have a flattened, unequal distribution that bulges within its edge. Between the stars is a dense interstellar medium full of heavy elements emitted by evolved stars. The diffuse stellar halo extends out to one million light years in diameter. Orbiting the galaxy is a very large population of globular clusters. NGC 4889 is also a strong source of soft X-ray, ultraviolet, and radio frequency radiation.
As the largest and the most massive galaxy easily visible to Earth, NGC 4889 has played an important role in both amateur and professional astronomy, and has become a prototype in studying the dynamical evolution of other supergiant elliptical galaxies in the more distant universe.NGC 884
NGC 884 (also known as χ Persei) is an open cluster located 7600 light years away in the constellation of Perseus. It is the easternmost of the Double Cluster with NGC 869. NGC 869 and 884 are often designated h and χ Persei, respectively. The cluster is most likely around 12.5 million years old. Located in the Perseus OB1 association, both clusters are located physically close to one another, only a few hundred light years apart. The clusters were first recorded by Hipparchus, but have likely been known since antiquity.
The Double Cluster is a favorite of amateur astronomers. These bright clusters are often photographed or observed with small telescopes. Easy to find, the clusters are visible with the unaided eye between the constellations of Perseus and Cassiopeia as a brighter patch in the winter Milky Way. The Double Cluster was also included in the Caldwell catalogue, a catalogue of astronomical objects for amateur observation.In small telescopes the cluster appears as a beautiful assemblage of bright stars located in a rich star field. Dominated by bright blue stars the cluster also hosts a few orange stars that add to the visual interest. Both clusters together offer a spectacular low magnification view.Nebula
A nebula (Latin for "cloud" or "fog"; pl. nebulae, nebulæ, or nebulas) is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, the term was used to describe any diffuse astronomical object, including galaxies beyond the Milky Way. The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others.
Most nebulae are of vast size; some are hundreds of light years in diameter. A nebula that is barely visible to the human eye from Earth would appear larger, but no brighter, from close by. The Orion Nebula, the brightest nebula in the sky and occupying an area twice the diameter of the full Moon, can be viewed with the naked eye but was missed by early astronomers. Although denser than the space surrounding them, most nebulae are far less dense than any vacuum created on Earth – a nebular cloud the size of the Earth would have a total mass of only a few kilograms. Many nebulae are visible due to fluorescence caused by embedded hot stars, while others are so diffuse they can only be detected with long exposures and special filters. Some nebulae are variably illuminated by T Tauri variable stars.
Nebulae are often star-forming regions, such as in the "Pillars of Creation" in the Eagle Nebula. In these regions the formations of gas, dust, and other materials "clump" together to form denser regions, which attract further matter, and eventually will become dense enough to form stars. The remaining material is then believed to form planets and other planetary system objects.Owl Nebula
The Owl Nebula (also known as Messier 97, M97 or NGC 3587) is a planetary nebula located approximately 2,030 light years away in the constellation Ursa Major. It was discovered by French astronomer Pierre Méchain on February 16, 1781. When William Parsons, 3rd Earl of Rosse, observed the nebula in 1848, his hand-drawn illustration resembled an owl's head. It has been known as the Owl Nebula ever since.The nebula is approximately 8,000 years old. It is approximately circular in cross-section with a little visible internal structure. It was formed from the outflow of material from the stellar wind of the central star as it evolved along the asymptotic giant branch. The nebula is arranged in three concentric shells, with the outermost shell being about 20–30% larger than the inner shell. The owl-like appearance of the nebula is the result of an inner shell that is not circularly symmetric, but instead forms a barrel-like structure aligned at an angle of 45° to the line of sight.The nebula holds about 0.13 solar masses of matter, including hydrogen, helium, nitrogen, oxygen, and sulfur; all with a density of less than 100 particles per cubic centimeter. Its outer radius is around 0.91 ly (0.28 pc) and it is expanding with velocities in the range of 27–39 km/s into the surrounding interstellar medium.The 14th magnitude central star has since reached the turning point of its evolution where it condenses to form a white dwarf. It has 55–60% of the Sun's mass, 41–148 times the brightness of the Sun, and an effective temperature of 123,000 K. The star has been successfully resolved by the Spitzer Space Telescope as a point source that does not show the infrared excess characteristic of a circumstellar disk.Patrick Moore
Sir Patrick Alfred Caldwell-Moore, (4 March 1923 – 9 December 2012) was an English amateur astronomer who attained prominent status in that field as a writer, researcher, radio commentator and television presenter.Moore was President of the British Astronomical Association, co-founder and president of the Society for Popular Astronomy, author of over seventy books on astronomy, and presenter of the world's longest-running television series with the same original presenter, BBC's The Sky at Night. He became known as a specialist in Moon observation and for creating the Caldwell catalogue. Idiosyncrasies such as his rapid diction and monocle made him a popular and instantly recognisable figure on British television.
Moore was also a self-taught xylophonist, glockenspiel player and pianist, as well as an accomplished composer. He was an amateur cricketer, golfer and chess player. In addition to many popular science books, he wrote numerous works of fiction. He was an opponent of fox hunting, an outspoken critic of the European Union, supporter of the UK Independence Party and served as chairman of the short-lived anti-immigration United Country Party. He served in the Royal Air Force during World War II; Moore claimed that his fiancée was killed during the war, and he never married or had children.RCW Catalogue
The RCW Catalogue (from Rodgers, Campbell & Whiteoak) is an astronomical catalogue of Hα-emission regions in the southern Milky Way, described in (Rodgers et al. 1960). It contains 182 objects, including many of the earlier Gum catalogue (84 items) objects.
The later Caldwell catalogue included some objects from the RCW catalogue. There is also some overlap with the Sharpless catalogue-2 (312 items), although that primarily covered the northern hemisphere, whereas RCW and Gum primarily covered the southern hemisphere.
The RCW catalogue was compiled by Alexander William Rodgers, Colin T. Campbell and John Bartlett Whiteoak. They catalogued southern nebulae while working under Bart Bok at the Mount Stromlo Observatory in Australia in the 1960s.Sh2-155
Sh2-155 (also designated Sharpless 155 or S155) is a diffuse nebula in the constellation Cepheus, within a larger nebula complex containing emission, reflection, and dark nebulosity. It is widely known as the Cave Nebula, though that name was applied earlier to Ced 201, a different nebula in Cepheus. Sh2-155 is an ionized H II region with ongoing star formation activity, at an estimated distance of 725 parsecs (2400 light-years) from Earth.Sh2-155 was first noted as a galactic emission nebula in 1959 in the extended second edition of the Sharpless catalogue, being a part of the much larger Cep OB3 Association. Although Sh2-155 is relatively faint for amateur observation, some of its structure may be seen visually through a moderately sized telescope under dark skies.Sh2-155 lies at the edge of the Cepheus B cloud (part of the Cepheus molecular cloud), and is ionized by young stars from the Cep OB3 association. It has been suggested that radiation from the hot O-type star HD 217086 is compressing the region, triggering the formation of a new generation of stars. A study of the region's young stellar objects by the Chandra X-ray Observatory and Spitzer Space Telescope shows a progression of stellar ages in front of the cloud, supporting the hypothesis of triggered star-formation.Sharpless catalog
The Sharpless catalog is a list of 313 HII regions (emission nebulae), intended to be comprehensive north of declination −27°. (It does include some nebulae south of that declination as well.) The first edition was published in 1953 with 142 objects (Sh1), and the second and final version was published by US astronomer Stewart Sharpless in 1959 with 312 objects. Sharpless also includes some planetary nebulae and supernova remnants, in addition to HII regions.In 1953 Stewart Sharpless joined the staff of the United States Naval Observatory Flagstaff Station, where he surveyed and cataloged H II regions of the Milky Way using the images from the Palomar Sky Survey. From this work Sharpless published his catalog of H II regions in two editions, the first in 1953 with 142 nebula. The second and final edition was published in 1959 with 312 nebulae.Sharpless coordinates are based on the star catalogs Bonner Durchmusterung (BD) and Cordoba Durchmusterung (CD), but the second release was adjusted to the 1900 epoch.In the second release, some coordinates for southern hemisphere regions have an uncertainty over 1 minute of arc. This can make them difficult to find, so a revised catalog called BFS (Blitz, Fich and Stark) was released. BFS has 65 new regions and about 20 removals. Most of the removed items were taken out because they were the aforementioned nebula or remnants.The 312 items in Sharpless sometimes overlap with the 110 Messier objects (M), 7,840 objects in the New General Catalogue (NGC), the Caldwell catalogue (that itself is a "best of" from other catalogues, with 109 items), and the RCW catalog. Contemporary catalogs were Gum and RCW, but they mainly covered the southern hemisphere.