NGC 246 (also known as the Skull Nebula"The Night Sky", ''

Astronomy Now ''Astronomy Now'' is a monthly British magazine on astronomy and space. According to the Royal Astronomical Society, ''Astronomy Now'' is the "principal amateur astronomy magazine in Britain" with a reputed circulation of 24,000. The magazine f ...

'', Oct 2008. or Caldwell 56) is a

planetary nebula A planetary nebula (PN, plural PNe) is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Cetus Cetus () is a constellation, sometimes called 'the whale' in English. The Cetus (mythology), Cetus was a sea monster in Greek mythology which both Perseus and Heracles needed to slay. Cetus is in the region of the sky that contains other water- ...

. It is the first known planetary nebula to have a hierarchical triple star system at its center. The nebula and the stars associated with it are listed in several catalogs, as summarized by the

SIMBAD SIMBAD (the Set of Identifications, Measurements and Bibliography for Astronomical Data) is an astronomical database of objects beyond the Solar System. It is maintained by the Centre de données astronomiques de Strasbourg (CDS), France. SIMBA ...

database. NGC 246 was discovered by

William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...

in 1785. The nebula is roughly 1,600

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s away.Stephen James O'Meara, ''The Caldwell Objects'', Sky Publishing Corporation, , p 223. NGC 246's central star is the 12th magnitude

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...

HIP 3678 A. NGC 246 is not to be confused with the

Rosette Nebula The Rosette Nebula (also known as Caldwell 49) is an H II region located near one end of a giant molecular cloud in the Monoceros region of the Milky Way Galaxy. The open cluster NGC 2244 (Caldwell 50) is closely associated with the nebulosity, th ...

(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.David H. Levy, ''Deep Sky Objects'', Prometheus Books, 2005, , p 129.

Discovery and research

In 1785,

discovered NGC 246. In 2014, astronomers discovered a second companion to NGC 246's central star, HIP 3678 A, 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 The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 mem ...

Very Large Telescope The Very Large Telescope (VLT) is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each with a primary mirror 8.2 m across, ...

Image gallery

File:The Skull Nebula NGC246 Goran Nilsson & The Liverpool Telescope.jpg, HaRGB image of The Skull Nebula (NGC 246). Data from the

Liverpool Telescope The Liverpool Telescope (LT) is a two-metre-aperture robotic Ritchey–Chrétien telescope that observes autonomously (without human intervention). However professional astronomers, school groups and other credible registered users submit speci ...

, processed by Göran Nilsson. Total exposure time 1.1 hours. File:n246s.jpg, NGC 246 acquired using the Schulman 0.8m Telescope atop Mount Lemmon, AZ. This is a full color (visual) image.

References

External links

* Planetary nebulae Cetus 0246 056b 17841127 {{nebula-stub