NGC 246 (Caldwell 56) is known as the Skull Nebula, and sometimes also as the Pac-Man Nebula. This leads to some confusion with the Rosetta Nebula (NGC 2237), sometimes referred to as The Skull, and the Pac-Man Emission Nebula (NGC 281). NGC 246 is a planetary nebula located on Cetus. Although its brightness is low, it is accessible to 150 m aperture telescopes on dark nights. I was discovered by William Herschell in 1785. Its central star (HIP3678) is a white dwarf of magnitude 12. The star has two companions, one located 3.8 arc sec to the southeast, and another, a red dwarf, located 1 arc sec to the northeast
(Adam and Mugrauer 2014). It is the first known planetary nebula whose central star is a triple hierarchical system: the three rotate around its center of mass, two closer constituting a binary system and other solitary further from the center. NGC 246 is an evolved planetary about 6600 years old, and is expanding at 39.5 km/s. The peripheral ring (shock front) begins to fray due to interaction with the interstellar medium, and the ionized gases around the central star have an irregular structure due to interaction with the compressed gases on the periphery.
The image is composed in HII-G-OIII, with stars in RGB and a total exposure of 16h 53m. The shots were taken in December, with seeing not too good and Cetus near the contaminated horizon. This has penalized the resolution, already compromised by the small size of the object (4.1 arcmin). The background is poor in stars and very uniform. Meade ACF 12” f/8 OTA and ASI 2600M camera.
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