Monoceros (

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

: Μονόκερως, "

unicorn The unicorn is a legendary creature that has been described since antiquity as a beast with a single large, pointed, spiraling horn projecting from its forehead. In European literature and art, the unicorn has for the last thousand years o ...

") is a faint constellation on the

celestial equator The celestial equator is the great circle of the imaginary celestial sphere on the same plane as the equator of Earth. This plane of reference bases the equatorial coordinate system. In other words, the celestial equator is an abstract proj ...

. Its definition is attributed to the 17th-century Dutch cartographer

Petrus Plancius Petrus Plancius (; 1552 – 15 May 1622) was a Dutch-Flemish astronomer, cartographer and clergyman. He was born as Pieter Platevoet in Dranouter, now in Heuvelland, West Flanders. He studied theology in Germany and England. At the age of 24 he ...

. It is bordered by Orion to the west,

Gemini Gemini may refer to: Space * Gemini (constellation), one of the constellations of the zodiac ** Gemini in Chinese astronomy * Project Gemini, the second U.S. crewed spaceflight program * Gemini Observatory, consisting of telescopes in the Norther ...

to the north, Canis Major to the south, and Hydra to the east. Other bordering constellations include Canis Minor,

Lepus Hares and jackrabbits are mammals belonging to the genus ''Lepus''. They are herbivores, and live solitarily or in pairs. They nest in slight depressions called forms, and their young are able to fend for themselves shortly after birth. The gen ...

, and Puppis.

Features

Stars

Monoceros contains only a few fourth magnitude stars, making it difficult to see with the naked eye. Alpha Monocerotis has a

visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of 3.93, while for Gamma Monocerotis it is 3.98. Beta Monocerotis is a triple star system; the three stars form a fixed triangle. The visual magnitudes of the stars are 4.7, 5.2, and 6.1.

William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline ...

discovered it in 1781 and called it "one of the most beautiful sights in the heavens". Epsilon Monocerotis is a fixed

binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two digits (0 and 1) * Binary function, a function that takes two arguments * Binary operation, a mathematical operation that ta ...

, with visual magnitudes of 4.5 and 6.5. S Monocerotis, or 15 Monocerotis, is a bluish white

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

and is located at the center of NGC 2264. The variation in its magnitude is slight (4.2–4.6). It has a companion star of visual magnitude 8.

V838 Monocerotis V838 Monocerotis (Nova Monocerotis 2002) is a spectroscopic binary star system in the constellation Monoceros about 19,000 light years (6 kpc) from the Sun. The previously unremarked star was observed in early 2002 experiencing a major ...

, a variable

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Ant ...

star, had an outburst starting on January 6, 2002; in February of that year, its brightness increased by a factor of 10,000 in one day. After the outburst was over, the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

was able to observe a

light echo 309x309px, Reflected light following path B arrives shortly after the direct flash following path A but before light following path C. B and C have the same apparent distance from the star as seen from Earth.">Earth.html" ;"title="apparent distan ...

, which illuminated the dust surrounding the star. Monoceros also contains Plaskett's Star, a massive binary system whose combined mass is estimated to be that of almost 100 solar masses. Monoceros is the location of the binary system Scholz's Star, host to a red dwarf primary and

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

secondary; the system performed a close flypast of the solar system approximately 70,000 years ago, travelling within 120,000 astronomical units of the sun within the

Oort Cloud The Oort cloud (), sometimes called the Öpik–Oort cloud, first described in 1950 by the Dutch astronomer Jan Oort, is a theoretical concept of a cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from ...

. One of the nearest known black holes to our Solar System is in this constellation. The binary star system A0620-00 in the constellation of Monoceros is at a distance of roughly 3,300 light-years (1,000 parsecs) away. The black hole is estimated to be 6.6 solar masses.

Planets

Monoceros contains two super-Earth exoplanets in one planetary system: COROT-7b was detected by the

COROT CoRoT (French: ; English: Convection, Rotation and planetary Transits) was a space telescope mission which operated from 2006 to 2013. The mission's two objectives were to search for extrasolar planets with short orbital periods, particularly th ...

satellite and COROT-7c was detected by HARPS from ground-based telescopes. Until the announcement of Kepler-10b in January 2011, COROT-7b was the smallest exoplanet to have its diameter measured, at 1.58 times that of the Earth (which would give it a volume 3.95 times Earth's). Both planets in this system were discovered in 2009.

Deep-sky objects

Part of the galactic plane goes through Monoceros. Monoceros contains many clusters and nebulae, most notable among them are: * M50, an

open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, an ...

* The Rosette Nebula (NGC 2237, 2238, 2239, and 2246) is a diffuse nebula in Monoceros. It has an overall magnitude of 6.0 and is 4900 light-years from Earth. The Rosette Nebula, over 100 light-years in diameter, has an associated star cluster and possesses many

Bok globule In astronomy, Bok globules are isolated and relatively small dark nebulae, containing dense cosmic dust and gas from which star formation may take place. Bok globules are found within H II regions, and typically have a mass of about 2 to 50 solar ...

s in its dark areas. It was independently discovered in the 1880s by

Lewis Swift Lewis A. Swift (February 29, 1820 – January 5, 1913) was an American astronomer who discovered 13 comets and 1,248 previously uncatalogued nebulae. Only William Herschel discovered more nebulae visually. Discoveries Swift discovered or co-discov ...

(early 1880s) and

Edward Emerson Barnard Edward Emerson Barnard (December 16, 1857 – February 6, 1923) was an American astronomer. He was commonly known as E. E. Barnard, and was recognized as a gifted observational astronomer. He is best known for his discovery of the high proper mo ...

(1883) as they hunted for

comets A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...

. * The Christmas Tree Cluster (NGC 2264) is another open cluster in Monoceros. Named for its resemblance to a Christmas tree, it is fairly bright at an overall magnitude of 3.9; it is 2400 light-years from Earth. The

S Monocerotis represents the tree's trunk, while the variable star V429 Monocerotis represents its top. * The Cone Nebula (NGC 2264), associated with the Christmas Tree Cluster, is a very dim nebula that contains a dark conic structure. It appears clearly in photographs, but is very elusive in a telescope. The nebula contains several

Herbig–Haro object Herbig–Haro (HH) objects are bright patches of nebulosity associated with newborn stars. They are formed when narrow jets of partially ionised gas ejected by stars collide with nearby clouds of gas and dust at several hundred kilometres per s ...

s, which are small irregularly variable nebulae. They are associated with

protostar A protostar is a very young star that is still gathering mass from its parent molecular cloud. The protostellar phase is the earliest one in the process of stellar evolution. For a low-mass star (i.e. that of the Sun or lower), it lasts about 50 ...

s. * NGC 2254 is an open cluster with an overall magnitude of 9.7, 7100 light-years from Earth. It is a Shapley class f and Trumpler class I 2 p cluster, meaning that it appears to be a fairly rich cluster overall, though it has fewer than 50 stars. It appears distinct from the background star field and is very concentrated at its center; its stars range moderately in brightness. * Hubble's Variable Nebula (NGC 2261) is a nebula with an approximate magnitude of 10, 2500 light-years from Earth. Though it is named for Edwin Hubble, it was discovered in 1783 by

. Hubble's Variable Nebula is illuminated by R Monocerotis, a young variable star embedded in the nebula; the star's unique interaction with the material in the nebula makes it both an

emission nebula 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 emissio ...

and a reflection nebula. One hypothesis regarding their interaction is that the nebula and its illuminating star are a very early stage planetary system. * IC 447, a reflection nebula.

History

In Western astronomy, Monoceros is a relatively modern constellation, not one of

Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importance ...

's 48 in the '' Almagest''. Its first certain appearance was on a globe created by the Dutch cartographer

in 1612 or 1613 and it was later charted by German astronomer Jakob Bartsch as Unicornu on his star chart of 1624. German astronomers

Heinrich Wilhelm Olbers Heinrich Wilhelm Matthias Olbers (; ; 11 October 1758 – 2 March 1840) was a German physician and astronomer. Life and career Olbers was born in Arbergen, Germany, today part of Bremen, and studied to be a physician at Göttingen (1777–80 ...

and Ludwig Ideler indicate (according to

Richard Hinckley Allen In astronomy, stars have a variety of different stellar designations and names, including catalogue designations, current and historical proper names, and foreign language names. Only a tiny minority of known stars have proper names; all others ha ...

's allegations) that the constellation may be older, quoting an astrological work from 1564 that mentioned "the second horse between the

Twins Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of TwinLast Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two em ...

and the Crab has many stars, but not very bright"; these references may ultimately be due to the 13th century Scotsman

Michael Scot Michael Scot (Latin: Michael Scotus; 1175 – ) was a Scottish mathematician and scholar in the Middle Ages. He was educated at Oxford and Paris, and worked in Bologna and Toledo, where he learned Arabic. His patron was Frederick II of the H ...

, but refer to a horse and not a unicorn, and its position does not quite match. Joseph Scaliger is reported to have found Monoceros on an ancient

Persian Persian may refer to: * People and things from Iran, historically called ''Persia'' in the English language ** Persians, the majority ethnic group in Iran, not to be conflated with the Iranic peoples ** Persian language, an Iranian language of the ...

sphere. French astronomer

Camille Flammarion Nicolas Camille Flammarion FRAS (; 26 February 1842 – 3 June 1925) was a French astronomer and author. He was a prolific author of more than fifty titles, including popular science works about astronomy, several notable early science fic ...

believed that a former constellation, Neper (the "Auger"), occupied the area of the sky now home to Monoceros and

Microscopium Microscopium ("the Microscope") is a minor constellation in the southern celestial hemisphere, one of twelve created in the 18th century by French astronomer Nicolas-Louis de Lacaille and one of several depicting scientific instruments. The n ...

, but this is disputed.Allen, p. 290. Chinese asterisms Sze Fūh, the Four Great Canals; Kwan Kew; and Wae Choo, the Outer Kitchen, all lay within the boundaries of Monoceros.

Citations

References

* *

External links

VISTA Reveals the Secret of the Unicorn
— ESO Photo Release
The Deep Photographic Guide to the Constellations: Monoceros

{{DEFAULTSORT:Constellation, Monoceros Equatorial constellations Constellations listed by Petrus Plancius Dutch celestial cartography in the Age of Discovery Astronomy in the Dutch Republic 1610s in the Dutch Republic Unicorns