NGC 1931

{{Short description|Nebula and open cluster in the constellation Auriga}}

{{Infobox nebula

| image = NGC1931HunterWilson.jpg

| caption = NGC 1931

| credit =

| name = NGC 1931

| type = Reflection

| type2 = emission nebula

| epoch = J2000.0

| ra = {{RA|5|31}}{{cite simbad

| title=NGC 1931

| access-date=2008-11-16}}

| dec = {{DEC|+34|15}}

| dist_ly = ~7500

| appmag_v = 10.1

| size_v = 7′

| constellation = Auriga

| radius_ly =

| absmag_v =

| notes =

| names =

|}}

NGC 1931 is a reflection and emission nebula and around a young star cluster in the constellation Auriga. The nebula shares similarities to the Orion Nebula as it is a mixed emission-reflection nebula that also contains a small Trapezium of hot young stars.{{Cite journal |last=Ambartsumian |first=V. A. |date=1954-01-01 |title=Multiple Systems of Trapezium type |url=https://ui.adsabs.harvard.edu/abs/1954CoBAO..15....3A/abstract |journal=Communications of the Byurakan Astrophysical Observatory |volume=15 |pages=3–40|bibcode=1954CoBAO..15....3A }} At around 2 million years of age,{{Cite journal |last1=Lim |first1=Beomdu |last2=Sung |first2=Hwankyung |last3=Bessell |first3=Michael S. |last4=Kim |first4=Jinyoung S. |last5=Hur |first5=Hyeonoh |last6=Park |first6=Byeong-Gon |date=2015-04-01 |title=The Sejong Open Cluster Survey (SOS). IV. the Young Open Clusters NGC 1624 and NGC 1931 |url=https://ui.adsabs.harvard.edu/abs/2015AJ....149..127L/abstract |journal=The Astronomical Journal |volume=149 |issue=4 |pages=127 |doi=10.1088/0004-6256/149/4/127 |arxiv=1502.00105 |bibcode=2015AJ....149..127L |hdl=1885/14284 |issn=0004-6256}} most of the ongoing star formation in the star cluster is hidden away in the nebula.{{Cite journal |last1=Dewangan |first1=L. K. |last2=Ojha |first2=D. K. |last3=Zinchenko |first3=I. |last4=Janardhan |first4=P. |last5=Luna |first5=A. |date=2017-01-01 |title=Multiwavelength Study of the Star Formation in the S237 H II Region |journal=The Astrophysical Journal |volume=834 |issue=1 |pages=22 |doi=10.3847/1538-4357/834/1/22 |doi-access=free |arxiv=1610.08428 |bibcode=2017ApJ...834...22D |issn=0004-637X}} It is believed that the main ionizing source for the dusty molecular cloud is a single, hot B-type star. The distance from Earth is estimated at 7500 light years.