Planetary nebula in the constellation Cetus
NGC 246 (also known as the Skull Nebula 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. 
The nebula is roughly away. NGC 246's central star is the 12th magnitude white dwarf HIP 3678 A. 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. 
NGC 246 is not to be confused with the Rosette Nebula (NGC 2337), which is also referred to as the "Skull." 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.
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