Editing Monoceros (section)

== Features ==
[[Image:MonocerosCC.jpg|thumb|left|200px|The constellation Monoceros as it can be seen by the naked eye.]]

===Stars===
{{See also|List of stars in Monoceros}}
Monoceros contains only a few fourth magnitude stars, making it difficult to see with the naked eye. [[Alpha Monocerotis]] has a [[visual magnitude]] 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]] discovered it in 1781 and called it "one of the most beautiful sights in the heavens".{{Citation needed|date=April 2023}}

[[Epsilon Monocerotis]] is a fixed [[binary star|binary]], with visual magnitudes of 4.5 and 6.5.

[[S Monocerotis]], or 15 Monocerotis, is a bluish white [[variable star]] 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]], a variable [[red supergiant]] 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]] was able to observe a [[light echo]], which illuminated the dust surrounding the star.<ref name="objects">{{cite book |last1=Wilkins |first1=Jamie |url=https://archive.org/details/300astronomicalo0000wilk |title=300 Astronomical Objects: A Visual Reference to the Universe |last2=Dunn |first2=Robert |date=2006 |publisher=Firefly Books |isbn=978-1-55407-175-3 |edition=1st |location=Buffalo, New York |url-access=registration}}</ref>

Monoceros also contains [[Plaskett's Star]], a massive binary system whose combined mass is estimated, per 2008 calculations, to be almost 100 solar masses.<ref name=aaa489_2_713>{{citation | display-authors=1 | last1=Linder | first1=N. | last2=Rauw | first2=G. | last3=Martins | first3=F. | last4=Sana | first4=H. | last5=De Becker | first5=M. | last6=Gosset | first6=E. | title=High-resolution optical spectroscopy of Plaskett's star | journal=Astronomy and Astrophysics | volume=489 | issue=2 | pages=713–723 |date=October 2008 | doi=10.1051/0004-6361:200810003 | bibcode=2008A&A...489..713L |arxiv = 0807.4823 | s2cid=118431215 }}</ref>

Monoceros is the location of the binary system [[Scholz's Star]], host to a [[red dwarf]] primary and [[brown dwarf]] 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]].<ref name="Mamajek2015">{{cite journal |last1=Mamajek |first1=Eric E. |last2=Barenfeld |first2=Scott A. |last3=Ivanov |first3=Valentin D. |year=2015 |title=The Closest Known Flyby of a Star to the Solar System |journal=[[The Astrophysical Journal]] |volume=800 |issue=1 |pages=L17 |arxiv=1502.04655 |bibcode=2015ApJ...800L..17M |doi=10.1088/2041-8205/800/1/L17 |s2cid=40618530 |doi-access=free}}</ref>

One of the nearest known [[black hole]]s to the 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 [[exoplanet]]s in one [[planetary system]]: [[CoRoT-7b]] was detected by the [[CoRoT]] satellite and [[CoRoT-7c]] was detected by the [[High Accuracy Radial Velocity Planet Searcher]] 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, so background galaxies are concealed by [[interstellar dust]]. Monoceros contains many clusters and nebulae; most notable among them are:
* [[Messier 50]], an [[open cluster]]
* 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]]s in its dark areas. It was independently discovered in the 1880s by [[Lewis Swift]] (early 1880s) and [[Edward Emerson Barnard]] (1883) as they hunted for [[comets]].{{sfn|Levy|2005|p=104}}
* 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 variable star S Monocerotis represents the tree's trunk, while the variable star [[V429 Monocerotis]] represents its top.{{sfn|Levy|2005|pp=82-83}}<ref name="NYT-20231219">{{cite news |last=Miller |first=Katrina |title=It's Christmastime in the Cosmos - Astronomers have a long tradition of finding holiday cheer in outer space. |url=https://www.nytimes.com/2023/12/19/science/christmas-stars-galaxies-webb-nasa.html |date=19 December 2023 |work=[[The New York Times]] |url-status=live |archiveurl=https://archive.today/20231219114751/https://www.nytimes.com/2023/12/19/science/christmas-stars-galaxies-webb-nasa.html |archivedate=19 December 2023 |accessdate=19 December 2023 }}</ref>
* 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]]s, which are small irregularly variable nebulae. They are associated with [[protostar]]s.{{sfn|Levy|2005|p=83}}
* [[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.{{sfn|Levy|2005|p=85}}
* [[Hubble's Variable Nebula]] (NGC 2261) is a nebula with an approximate magnitude of 10, 2500 light-years from Earth. It is named for [[Edwin Hubble]], and was discovered in 1783 by Herschel. 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]] and a [[reflection nebula]]. One hypothesis regarding their interaction is that the nebula and its illuminating star are a very early stage planetary system.{{sfn|Levy|2005|pp=105-106}}
*[[IC 447]], a reflection nebula.