NGC 6946, sometimes referred to as the
Fireworks Galaxy, is a face-on
intermediate spiral galaxy with a small bright nucleus, whose location in the sky straddles the boundary between the
northernconstellations of
Cepheus and
Cygnus. Its distance from Earth is about 25.2 million
light-years or 7.72
megaparsecs, similar to the distance of
M101 (NGC 5457) in the
constellationUrsa Major. Both were once considered to be part of the
Local Group, but are now known to be among the dozen bright spiral galaxies near the
Milky Way but beyond the confines of the Local Group. NGC 6946 lies within the
Virgo Supercluster.The galaxy was discovered by
William Herschel on 9 September 1798. Based on an estimation by the Third Reference Catalogue of Bright Galaxies (RC3) in 1991, the galaxy has a
D25 B-band isophotal diameter of 26.77
kiloparsecs (87,300
light-years). It is heavily obscured by
interstellar matter due to its location close to the
galactic plane of the Milky Way. Due to its prodigious star formation it has been classified as an active
starburst galaxy. NGC 6946 has also been classified as a double-barred spiral galaxy, with the inner, smaller bar presumably responsible for funneling gas into its center.Various unusual celestial objects have been observed within NGC 6946. This includes the so-called 'Red Ellipse' along one of the northern arms that looks like a super-bubble or very large supernova remnant, and which may have been formed by an open cluster containing massive stars. There are also two regions of unusual dark lanes of
nebulosity, while within the spiral arms several regions appear devoid of stars and gaseous hydrogen, some spanning up to two kiloparsecs across. A third peculiar object, discovered in 1967, is now known as "Hodge's Complex". This was once thought to be a young
supergiant cluster, but in 2017 it was conjectured to be an interacting dwarf galaxy superimposed on NGC 6946.
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