NGC 2403
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NGC 2403 (also known as Caldwell 7) is an
intermediate spiral galaxy An intermediate spiral galaxy is a galaxy that is in between the classifications of a barred spiral galaxy and an unbarred spiral galaxy. It is designated as SAB in the galaxy morphological classification system devised by Gerard de Vaucouleur ...
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 ...
Camelopardalis Camelopardalis is a large but faint constellation of the northern sky representing a giraffe. The constellation was introduced in 1612 or 1613 by Petrus Plancius. Some older astronomy books give Camelopardalus or Camelopardus as alternative form ...
. It is an outlying member of the
M81 Group The M81 Group is a galaxy group in the constellations Ursa Major and Camelopardalis that includes the galaxies Messier 81 and Messier 82, as well as several other galaxies with high apparent brightnesses. The approximate center of the group is ...
, and is approximately 8 million
light-year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astr ...
s distant. It bears a similarity to M33, containing numerous star-forming
H II region An H II region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light year ...
s, but being a little bit larger at approximately 90,000 light-years in diameter compared to the 61,100 light-year diameter of M33. The northern spiral arm connects it to the star forming region NGC 2404. NGC 2403 can be observed using 10×50
binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...
. NGC 2404 is 940 light-years in diameter, making it one of the largest known H II regions. This H II region represents striking similarity with
NGC 604 NGC 604 is an H II region inside the Triangulum Galaxy. It was discovered by William Herschel on September 11, 1784. It is among the largest H II regions in the Local Group of galaxies; at the galaxy's estimated distance of 2.7 million light-ye ...
in M33, both in size and location in galaxy.


Supernovae and Supernovae Imposters

There have been four reported astronomical transients in the galaxy: * SN 1954J was first noticed by
Gustav Tammann Gustav Andreas Tammann (24 July 1932 – 6 January 2019) was a Swiss astronomer and academic. He served as director of the Astronomical Institute of the University of Basel; as a member of the European Space Agency Space Telescope Advisory Team, ...
and
Allan Sandage Allan Rex Sandage (June 18, 1926 – November 13, 2010) was an American astronomer. He was Staff Member Emeritus with the Carnegie Observatories in Pasadena, California. He determined the first reasonably accurate values for the Hubble const ...
as a "bright blue irregular variable" star, which they named V12. They noted it underwent a major outburst on 2/3 November 1954, which attained a magnitude of 16 at its brightest. In 1972,
Fritz Zwicky Fritz Zwicky (; ; February 14, 1898 – February 8, 1974) was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical an ...
classified this event as a type V
supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
. It was later determined to be a
supernova imposter Supernova impostors are stellar explosions that appear at first to be a supernova but do not destroy their progenitor stars. As such, they are a class of extra-powerful novae. They are also known as Type V supernovae, Eta Carinae analogs, and g ...
: a highly luminous, very massive eruptive star, surrounded by a dusty nebula, similar to the 1843 Great Eruption of η Carinae in the Milky Way. * SN 2002 kg was discovered by LOTOSS (
Lick Observatory The Lick Observatory is an astronomical observatory owned and operated by the University of California. It is on the summit of Mount Hamilton (California), Mount Hamilton, in the Diablo Range just east of San Jose, California, United States. The ...
and Tenagra Observatory Supernova Searches) on 26 October 2002 and initially classified as a type IIn, or possibly the outburst of a
luminous blue variable Luminous blue variables (LBVs) are rare, massive, evolved stars that show unpredictable and sometimes dramatic variations in their spectra and brightness. They are also known as S Doradus variables after S Doradus, one of the brightest stars of th ...
. On 24 August 2021, it was reclassified as a Gap transient. * SN 2004dj ( type II-P, mag. 11.2) was discovered by
Kōichi Itagaki is an amateur astronomer based in Yamagata, the capital city of Yamagata Prefecture in the Tōhoku region of northern Honshu island, Japan. He is responsible for discovering many comets, and over 170 supernovae.Catalina Real-time Transient Survey The Catalina Real-Time Transient Survey is a collaboration using three telescopes looking for optical transients. The same telescopes are used as in the Catalina Sky Survey. They are Mt. Lemmon Survey, Catalina Sky Survey, and Siding Spring Surv ...
(CRTS) and Stan Howerton in December 2013. Outbursts from this star have been observed as recently as November 2021.


History

The galaxy was discovered by German-British astronomer
William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...
on 1 November 1788.
Edwin Hubble Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. He played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology. Hubble proved that many objects previously ...
detected
Cepheid variable A Cepheid variable () is a type of variable star that pulsates radially, varying in both diameter and temperature. It changes in brightness, with a well-defined stable period (typically 1–100 days) and amplitude. Cepheids are important cosmi ...
s in NGC 2403 using the
Hale Telescope The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in San Diego County, California, US, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation in 1928, he orchestrated the planning, de ...
, making it the first galaxy beyond the
Local Group The Local Group is the galaxy group that includes the Milky Way, where Earth is located. It has a total diameter of roughly , and a total mass of the order of . It consists of two collections of galaxies in a " dumbbell" shape; the Milky Way ...
within which a Cepheid was discovered. By 1963, 59 variables had been found in NGC 2403, of which 17 were eventually confirmed as Cepheids, with periods between 20 and 87 days. As late as 1950 Hubble was using a distance of just under 2 million light years for the galaxy's distance, but by 1968 the analysis of the Cepheids increased this by almost a factor of five, to within 0.2 magnitudes of the current value.


Companions

NGC 2403 has two known companions. One is the relatively massive dwarf galaxy DDO 44. It is currently being disrupted by NGC 2403, as evidenced by a tidal stream extending on both sides of DDO 44. DDO 44 is approaching NGC 2403 at a distance much closer than typical for dwarf galaxy interactions. It currently has a V-band absolute magnitude of −12.9, but its progenitor was even more luminous. The other known companion is officially named MADCASH J074238+652501-dw, although it is nicknamed MADCASH-1. The name refers to the MADCASH (Magellanic Analog Dwarf Companions and Stellar Halos) project. MADCASH-1 is similar to typical
dwarf spheroidal galaxies A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and as systems that are c ...
in the Local Group; it is quite faint, with an absolute V-band magnitude of −7.81, and has only an ancient, metal-poor population of
red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...
stars.


See also

*
Triangulum Galaxy The Triangulum Galaxy is a spiral galaxy 2.73 million light-years (ly) from Earth in the constellation Triangulum. It is catalogued as Messier 33 or NGC 598. With the D25 isophotal diameter of , the Triangulum Galaxy is the third-largest me ...
- looks very similar to NGC 2403.


References


External links


Spiral Galaxy NGC 2403
at the astro-photography site of Mr. Takayuki Yoshida
NGC 2403
at ESA/Hubble * *

– NGC 2403 {{Camelopardalis Intermediate spiral galaxies M81 Group Camelopardalis 2403 03918 21396 007b Astronomical objects discovered in 1788 Discoveries by William Herschel