| Emission nebula | |
|---|---|
| Planetary nebula | |
 | |
| Observation data:J2000epoch | |
| Right ascension | 00h 47m 03.338s[1] |
| Declination | −11° 52′ 18.94″[1] |
| Distance | 3,500+720 −850[2] ly |
| Apparent magnitude (V) | 8[3] / 11.8 (central star)[1] |
| Apparent dimensions (V) | 3.8′[3] |
| Constellation | Cetus |
| Physical characteristics | |
| Radius | 2-3[4] ly |
| Designations | Skull Nebula,[5] Pac-Man Nebula,[6]Caldwell 56,HIP 3678, PMN J0047-1152, 2E 178, PN VV 4,IRAS 00445-1207, MCT 0044-1208[1] |
| See also:Lists of nebulae | |
NGC 246 (also known as theSkull Nebula[5] orCaldwell 56) is aplanetary nebula in theconstellationCetus. It was discovered in 1785 byWilliam Herschel. The nebula and the stars associated with it are listed in several catalogs, as summarized by theSIMBAD database.[1]
The nebula is roughly3,500+720
−850 light-years away.[2] NGC 246's central star is the 12th magnitude[7]white dwarf HIP 3678 A.[8] 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 theEuropean Southern Observatory'sVery Large Telescope. This makes NGC 246 the first planetary nebula to have ahierarchical triple star system at its center.[9] It is currently the only known example of a planetary nebula with more than two central stars.[10]
NGC 246 is not to be confused with theRosette Nebula (NGC 2237), which is also referred to as the "Skull."[11] 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.[6]
Media related toNGC 246 at Wikimedia Commons
