NGC 2174

{{Short description|Emission nebula in the constellation Orion}}

{{Use dmy dates|date=April 2020}}

{{Infobox nebula |

| image = File:NGC-2174.tif

| caption= Monkey Head Nebula in Narrowband Sulfur-Hydrogen Alpha- Oxygen with a 1000mm telescope

| name = NGC 2174

| epoch = J2000

| type = H II region

| constellation = Orion

| ra = {{RA|06|09.7}}{{cite simbad

| title=NGC 2174

| access-date=13 July 2011}}

| dec = {{DEC|+20|30}}

| dist_ly = 6,400{{Citation needed|date=February 2007}}

| dist_pc = 2,000

| appmag_v = 6.8{{Citation needed|date=February 2007}}

| size_v = 40{{prime}}{{Citation needed|date=February 2007}}

| mass_kg =

| mass_msol =

| radius_ly =

| v_hb =

| age =

| notes =

| names =

}}

NGC 2174 (also known as Monkey Head Nebula) is an H II emission nebula located in the constellation Orion and is associated with the open star cluster NGC 2175. It was discovered on 6 February 1877 by French astronomer Édouard Stephan.{{cite web | url = https://cseligman.com/text/atlas/ngc21a.htm#2174 | title = New General Catalogue Objects: NGC{{nbsp}}2174 | last = Seligman | first = Courtney | website = Celestial Atlas | access-date = 27 August 2024 }} It is thought to be located about 6,400 light-years away from Earth. The nebula may have formed through hierarchical collapse.{{cite conference

| author=Cotera, A. |display-authors=4 | author2=Hester, J. | author3=Healy, K. | author4=Snider, K. | author5=Simpson, J. | author6=Whitney, B.

| title=Using Spitzer IRAC observations to Compare Modes of Star Formation in G305.35+0.7 and NGC 2174/5

| conference=Triggered Star Formation in a Turbulent ISM, International Astronomical Union Symposium

| date=August 2006

| location=Prague, Czech Republic

| id=S237, #98

| publication-date=2006

| bibcode=2006IAUS..237E..98C }}{{Dead link|date=July 2010}}

There is some equivocation in the use of the identifiers NGC 2174 and NGC 2175. These may apply to the entire nebula, to its brightest knot, or to the star cluster it includes. Burnham's Celestial Handbook lists the entire nebula as 2174/2175 and does not mention the star cluster.Robert Burnham, Jr, Burnham's Celestial Handbook, Dover, 1978, p. 1280. The NGC Project (working from the original descriptive notes) assigns NGC 2174 to the prominent knot at J2000 {{RA|06|09|23.7}}, {{DEC|+20|39|34}} and NGC 2175 to the entire nebula, and by extension to the star cluster.{{cite web

|url=http://www.ngcicproject.org/pubdb.htm

|title=Public Database

|at=Results for NGC 2174 and NGC 2175

|website=NGC/IC Project

|access-date=12 January 2014

|archive-url=https://web.archive.org/web/20090528100240/http://www.ngcicproject.org/pubdb.htm

|archive-date=28 May 2009

|url-status=dead

}} SIMBAD uses NGC 2174 for the nebula and NGC 2175 for the star cluster.

{{cite web

| title=SIMBAD Astronomical Database

| work=Results for NGC 2175

| url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=ngc+2175&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id

| access-date=13 January 2014

}}

Glowing gas and dark dust do not survive well in the Monkey Head Nebula. Young stars near the center of the nebula generate stellar winds and high energy radiation that causes the nebula's material to shift into complex shapes.{{Cite journal |date=Aug 4, 2014 |title=Monkey See, Monkey Do |journal=Astronomy |volume=42 |pages=10}} The nebula is primarily composed of hydrogen which glows at infrared wavelengths due to the radiation.{{Cite web |date=Mar 17, 2014 |title=Pillars in the Monkey Head Nebula |url=https://hubblesite.org/contents/media/images/3887-Image?Collection=Hubble%20Heritage&page=3}}