NGC 246

{{Short description|Planetary nebula in the constellation Cetus}}

{{Planetary nebula

| image = 300px

| caption=An infrared Spitzer Space Telescope image of NGC 246.
Credit: NASA/JPL.

| name = NGC 246

| type = Planetary

| epoch = J2000

| ra = {{RA|00|47|03.338}}

| dec = {{DEC|-11|52|18.94}}

| dist_ly = {{Val|{{convert|1080|pc|ly|disp=number}}|{{convert|220|pc|ly|disp=number}}|{{convert|260|pc|ly|disp=number}}|fmt=commas}}

| appmag_v = 8 / 11.8 (central star)

| size_v = 3.8{{prime}}{{cite web

| title=SEDS NGC Catalog Online

| work=Results for NGC 246

| url=http://spider.seds.org/ngc/ngc.cgi?NGC+246

| access-date=2010-11-29}}

| constellation = Cetus

| radius_ly = 2-3{{cite web

| title=NGC 246

| work=Astronomy: Stars & Planets

| url=http://jumk.de/astronomie/special-stars/ngc-246.shtml

| access-date=2013-01-07}}

| absmag_v =

| notes =

| names = Skull Nebula, Pac-Man Nebula, Caldwell 56, HIP 3678, PMN J0047-1152, 2E 178, PN VV 4, IRAS 00445-1207, MCT 0044-1208

}}

NGC 246 (also known as the Skull Nebula"The Night Sky", Astronomy Now, Oct 2008. or Caldwell 56) is a planetary nebula in the constellation Cetus. It was discovered in 1785 by William Herschel. The nebula and the stars associated with it are listed in several catalogs, as summarized by the SIMBAD database.{{cite simbad

| title=NGC 246

| access-date=2006-12-22}}

The nebula is roughly {{Val|{{convert|1080|pc|ly|disp=number}}|{{convert|220|pc|ly|disp=number}}|{{convert|260|pc|ly|disp=number}}|fmt=commas|u=light-years}} away.{{Cite journal |last=Löbling |first=Lisa |date=2018-06-01 |title=Sliding along the Eddington Limit—Heavy-Weight Central Stars of Planetary Nebulae |journal=Galaxies |volume=6 |issue=2 |pages=65 |arxiv=1806.07279 |doi=10.3390/galaxies6020065|doi-access=free |bibcode=2018Galax...6...65L }} NGC 246's central star is the 12th magnitudeStephen James O'Meara, The Caldwell Objects, Sky Publishing Corporation, {{ISBN|0-933346-97-2}}, p 223. white dwarf HIP 3678 A.{{Cite journal |last1=Adam |first1=C. |last2=Mugrauer |first2=M. |date=2014-11-01 |title=HIP 3678: a hierarchical triple stellar system in the centre of the planetary nebula NGC 246 |journal=Monthly Notices of the Royal Astronomical Society |volume=444 |issue=4 |pages=3459–3465 |doi=10.1093/mnras/stu1677 |doi-access=free |issn=0035-8711|arxiv=1409.5339 |bibcode=2014MNRAS.444.3459A }} In 2014, astronomers discovered a second companion to NGC 246's central star, which has a comoving companion star called HIP 3678 B. The second companion star, a red dwarf known as HIP 3678 C, was discovered using the European Southern Observatory's Very Large Telescope. This makes NGC 246 the first planetary nebula to have a hierarchical triple star system at its center.{{Cite web |last=information@eso.org |title=Stars and Skulls: new ESO image reveals eerie nebula |url=https://www.eso.org/public/news/eso2019/ |access-date=2023-03-09 |website=www.eso.org |language=en}}

NGC 246 is not to be confused with the Rosette Nebula (NGC 2237), which is also referred to as the "Skull."{{cite web | url=https://www.cnn.com/2018/02/14/world/rosette-nebula-heart/index.html | title=A hole in the heart of the Rosette Nebula | website=CNN | date=14 February 2018 }} Among some amateur astronomers, NGC 246 is known as the "Pac-Man Nebula" because of the arrangement of its central stars and the surrounding star field.David H. Levy, Deep Sky Objects, Prometheus Books, 2005, {{ISBN|1-59102-361-0}}, p 129.