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Abell 12, also known as PNG 198.6-06.3, PK 198-06.1 and ARO 220, is a 
planetary nebula
A planetary nebula 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 planets. The ...
located 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 first constellati ...
of Orion
Orion may refer to:
Common meanings
* Orion (constellation), named after the mythical hunter
* Orion (mythology), a hunter in Greek mythology
Arts and media
Fictional entities Characters and species
* Orion (character), a DC Comics c ...
. The nebula is 6,900 light year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...
s away from Earth, north of Betelgeuse
Betelgeuse is a red supergiant star in the constellation of Orion (constellation), Orion. It is usually the List of brightest stars, tenth-brightest star in the night sky and, after Rigel, the second brightest in its constellation. It i ...
. Abell 12 is known as "the hidden planetary" because of the foreground star Mu Orionis making it difficult to observe and Abell 12 being at an apparent magnitude
Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
of about 14. The best way for it to be observed is through narrowband filters such as H-alpha and O-III. The northern outer red hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
shell has been ruptured allowing the interior oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
to spill out.
References
External links
* * Abell 12 12 Orion (constellation) {{nebula-stub