View source for NGC 2403

{{Short description|Galaxy in the constellation Camelopardalis}}
{{Infobox Galaxy
| image = NGC2403-Subaru-HST-L.jpg
| caption = A [[Hubble Space Telescope]] (HST), and Subaru image of NGC 2403. [[NGC 2404]] is visible
| name = [[New General Catalogue|NGC]] 2403
| epoch = [[Epoch (astronomy)#Julian years and J2000|J2000]]
| type = SAB(s)cd<ref name="ned" />
| ra = {{RA|07|36|51.298}}<ref name="ned" />
| dec = {{DEC|+65|36|09.662}}<ref name="ned" />
| dist_ly = [[1 E22 m|9.65]] [[light-year|Mly]] (2.96 [[parsec|Mpc]])<ref name=jeffrey />
| z = 0.000445<ref name="ned" />
| h_radial_v = 133 ± 0 km/s<ref name="ned" />
| appmag_v = 8.9<ref name="ned" />
| size_v = {{Val|21.9|×|12.3|u=arcminute}}<ref name="ned" />
| size = ~{{convert|27.69|kpc|ly|abbr=on|lk=on|order=flip}} (estimated)<ref name ="ned" />
| constellation name = [[Camelopardalis]]
| notes = 
| names = {{odlist | name= Caldwell 7 | UGC= 3918 | PGC= 21396 | CGCG= 309-040 | MCG +11-10-007 | IRAS= 07321+6543}}<ref name="ned" /> 
}}

'''NGC 2403''' (also known as '''Caldwell 7''') is an [[intermediate spiral galaxy]] in the [[constellation]] [[Camelopardalis]]. It is an outlying member of the [[M81 Group]],<ref name="NSOG" /> and is approximately 8 million [[light-year]]s distant.

== Observation history ==
The galaxy was discovered by German-British astronomer [[William Herschel]] on 1 November 1788.<ref name="selig" /> [[Edwin Hubble]] detected [[Cepheid variable]]s in NGC 2403 using the [[Hale Telescope]], making it the first galaxy beyond the [[Local Group]] within which a Cepheid was discovered.<ref name="NSOG" /> 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.

==Characteristics==
[[File:A Galaxy of Birth and Death.jpg|thumb|left|A Galaxy of Birth and Death]]
NGC 2403 bears a similarity to [[Messier 33|M33]], containing numerous star-forming [[H II region]]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.<ref name="hoetal1997" /> It is a [[flocculent spiral galaxy]], with short, patchy arms.<ref name=Kostiuk>{{cite journal|last1=Kostiuk |first1=Valeria |last2=Marchuk |first2=Alexander |last3=Gusev |first3=Alexander |last4=Chugunov |first4=Ilia V. |title=A Comprehensive Analysis on the Nature of the Spiral Arms in NGC 3686, NGC 4321, and NGC 2403 |journal=Galaxies |date=2025 |volume=13 |issue=2 |page=27 |doi=10.3390/galaxies13020027 |doi-access=free |arxiv=2503.19587 |bibcode=2025Galax..13...27K }}</ref> The northern spiral arm connects it to the star forming region [[NGC 2404]].<ref name="NSOG" /> NGC 2403 can be observed using 10×50 [[binoculars]].<ref name="NSOG" /> [[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]] in M33, both in size and location in galaxy.

== Supernovae and supernovae imposters ==
There have been four reported [[Time-domain astronomy|astronomical transients]] in the galaxy:
* '''[[SN 1954J]]''' was first noticed by [[Gustav Andreas Tammann|Gustav Tammann]] and [[Allan Sandage]] as a "bright blue irregular variable" [[Star|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.<ref name=Tammann /> In 1972, [[Fritz Zwicky]] classified this event as a Type V [[supernova]].<ref name=Zwicky /> It was later determined to be a [[supernova imposter]]: a highly luminous, very massive eruptive star, surrounded by a dusty [[Nebula|nebula]], similar to the 1843 Great Eruption of [[Eta Carinae|η Carinae]] in the Milky Way.<ref name=VanDyk />
* '''SN 2002&nbsp;kg''' was discovered by LOTOSS ([[Lick Observatory]] and [[Tenagra_Observatories|Tenagra Observatory]] Supernova Searches) on 26 October 2002 and initially classified as a [[Type II supernova#Type IIn supernovae|Type IIn]], or possibly the outburst of a [[luminous blue variable]].<ref name=IAUC8051 /> On 24 August 2021, it was reclassified as a [[Calcium-rich supernova|Gap transient]].<ref name=TNS-2002kg />
* '''[[SN 2004dj]]''' ([[Type II supernova#Light curves for Type II-L and Type II-P supernovae|Type II-P]], mag. 11.2) was discovered by [[Kōichi Itagaki]] on 31 July 2004.{{r|IAUC-8377|TNS-2004dj}} At the time of its discovery, it was the nearest and brightest supernova observed in the 21st century, and is now listed as the brightest supernova of 2004.{{r|bishop}}
* '''AT{{nbsp}}2016ccd''', initially designated as SNhunt225, is a luminous blue variable, first discovered by [[Catalina Real-time Transient Survey]] (CRTS) and Stan Howerton in December 2013. Outbursts from this star have been observed as recently as November 2021.{{r|AT2016ccd|TNS-2016ccd}}

== Companions ==
NGC 2403 has two known companions. One is the relatively massive [[Dwarf galaxy|dwarf galaxy]] [[DDO 44]]. It is currently being disrupted by NGC 2403, as evidenced by a tidal stream extending {{cvt|25|kpc|kly|lk=on|order=flip}} 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.<ref name=jeffrey />

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]] 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]] stars.<ref name=Carlin2021 />

== See also ==
* [[Triangulum Galaxy]] - looks very similar to NGC 2403.
* [[List of NGC objects (2001–3000)]]

== References ==
{{reflist|refs=

<ref name="ned">{{cite web
| website = NASA/IPAC Extragalactic Database
| publisher = [[NASA]] and [[California Institute of Technology|Caltech]]
| title = Results for object NGC 2403
| url = https://ned.ipac.caltech.edu/byname?objname=NGC+2403
| access-date = 2006-11-21}}</ref>

<ref name=jeffrey>{{cite journal|arxiv=1906.08260|doi=10.3847/1538-4357/ab4c32|title=Tidal Destruction in a Low-mass Galaxy Environment: The Discovery of Tidal Tails around DDO 44|year=2019|last1=Carlin|first1=Jeffrey L.|last2=Garling|first2=Christopher T.|last3=Peter|first3=Annika H. G.|last4=Crnojević|first4=Denija|last5=Forbes|first5=Duncan A.|last6=Hargis|first6=Jonathan R.|last7=Mutlu-Pakdil|first7=Burçin|last8=Pucha|first8=Ragadeepika|last9=Romanowsky|first9=Aaron J.|last10=Sand|first10=David J.|last11=Spekkens|first11=Kristine|author11-link=Kristine Spekkens|last12=Strader|first12=Jay|last13=Willman|first13=Beth|journal=The Astrophysical Journal|volume=886|issue=2|page=109|bibcode=2019ApJ...886..109C|s2cid=195218404 |doi-access=free }}</ref>

<ref name="NSOG">{{cite book
 |last= Kepple
 |first= George Robert
 |author2=Glen W. Sanner
 |title= The Night Sky Observer's Guide
 |volume= 1
 |publisher= Willmann-Bell, Inc.
 |date= 1998
 |isbn= 978-0-943396-58-3
 |page=73
}}</ref>

<ref name="hoetal1997">{{cite journal
 | last1 = Ho
 | first1 = Luis C.
 | last2 = Filippenko
 | first2 = Alexei V.
 | last3 = Sargent
 | first3 = Wallace L. W.
 | title = A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies
 | date = October 1997
 | periodical = Astrophysical Journal Supplement
 | volume = 112
 | issue = 2
 | pages = 315–390
 | arxiv = astro-ph/9704107
 | bibcode = 1997ApJS..112..315H
 | doi = 10.1086/313041
 | s2cid = 17086638
 }}</ref>

<ref name=Tammann>{{cite journal | doi=10.1086/149487 | doi-access=free | title=The Stellar Content and Distance of the Galaxy NGC 2403 IN the M81 Group | date=1968 | last1=Tammann | first1=G. A. | last2=Sandage | first2=Allan | journal=The Astrophysical Journal | volume=151 | page=825 | bibcode=1968ApJ...151..825T}}</ref>

<ref name=Zwicky>{{cite journal | doi=10.1086/129392 | doi-access=free | title=The 1971 Palomar Supernova Search | date=1972 | last1=Kowal | first1=C. T. | last2=Sargent | first2=W. L. W. | last3=Searle | first3=L. | last4=Zwicky | first4=F. | journal=Publications of the Astronomical Society of the Pacific | volume=84 | issue=502 | page=844 | bibcode=1972PASP...84..844K}}</ref>

<ref name=VanDyk>{{cite journal|doi=10.1086/430238 |title=Supernova 1954J (Variable 12) in NGC 2403 Unmasked |date=2005 |last1=Van Dyk |first1=Schuyler D. |last2=Filippenko |first2=Alexei V. |last3=Chornock |first3=Ryan |last4=Li |first4=Weidong |last5=Challis |first5=Peter M. |journal=Publications of the Astronomical Society of the Pacific |volume=117 |issue=832 |pages=553–562 |arxiv=astro-ph/0503324 |bibcode=2005PASP..117..553V }}</ref>

<ref name=IAUC8051>{{cite journal |last1=Schwartz |first1=M. |last2=Li |first2=W. |last3=Filippenko |first3=A. V. |last4=Chornock |first4=R. |title=Supernova 2002kg in NGC 2403 |journal=International Astronomical Union Circular |volume=8051 |pages=1 |date=2003-01-01 |bibcode=2003IAUC.8051....1S |url=http://www.cbat.eps.harvard.edu/iauc/08000/08051.html#Item1}}</ref>

<ref name=TNS-2002kg>{{cite web | website=Transient Name Server | title=SN 2002&nbsp;kg | url=https://www.wis-tns.org/object/2002kg | publisher = [[International Astronomical Union|IAU]] | access-date=14 August 2024}}</ref>

<ref name=IAUC-8377>{{Cite journal |last1=Nakano |first1=S. |last2=Itagaki |first2=K. |last3=Bouma |first3=R. J. |last4=Lehky |first4=M. |last5=Hornoch |first5=K. |date=2004-08-01 |title=Supernova 2004dj in NGC 2403 |url=http://www.cbat.eps.harvard.edu/iauc/08300/08377.html#Item1 |journal=International Astronomical Union Circular |issue=8377 |pages=1 |bibcode=2004IAUC.8377....1N}} </ref>

<ref name=TNS-2004dj>{{cite web | website=Transient Name Server | title=SN 2004dj | url=https://www.wis-tns.org/object/2004dj |publisher = [[International Astronomical Union|IAU]] | access-date=14 August 2024}}</ref>

<ref name=bishop>{{cite web | url = https://www.rochesterastronomy.org/sn2004/index.html | title = Bright Supernovae - 2004 | last = Bishop | first = David | website = Rochester Astronomy | access-date = 21 August 2025}}</ref>

<ref name=AT2016ccd>{{cite web | url = https://www.rochesterastronomy.org/sn2013/sn2016ccd.html	| title = LBV AT2016ccd in NGC 2403 | last = Bishop | first = David | date = 9 November 2021 | website = Rochester Astronomy | access-date = 31 August 2024}}</ref>

<ref name=TNS-2016ccd>{{cite web | website=Transient Name Server | title=AT{{nbsp}}2016ccd | url=https://www.wis-tns.org/object/2016ccd | publisher = [[International Astronomical Union|IAU]] | access-date=31 August 2024}}</ref>

<ref name="selig">{{cite web | url = https://cseligman.com/text/atlas/ngc24.htm#2403 | title = New General Catalogue Objects: NGC 2403 | last = Seligman | first = Courtney | website = Celestial Atlas | access-date = 21 May 2025}}</ref>

<ref name=Carlin2021>{{cite journal|doi=10.3847/1538-4357/abe040|arxiv=2012.09174|bibcode=2021ApJ...909..211C|title=Hubble Space Telescope Observations of Two Faint Dwarf Satellites of Nearby LMC Analogs from MADCASH|year=2021|last1=Carlin|first1=Jeffrey L.|last2=Mutlu-Pakdil|first2=Burçin|last3=Crnojević|first3=Denija|last4=Garling|first4=Christopher T.|last5=Karunakaran|first5=Ananthan|last6=Peter|first6=Annika H. G.|last7=Tollerud|first7=Erik|last8=Forbes|first8=Duncan A.|last9=Hargis|first9=Jonathan R.|last10=Lim|first10=Sungsoon|last11=Romanowsky|first11=Aaron J.|last12=Sand|first12=David J.|last13=Spekkens|first13=Kristine|last14=Strader|first14=Jay|journal=The Astrophysical Journal|volume=909|issue=2|page=211|s2cid=229297953 |doi-access=free }}</ref>

}}

== External links ==
{{Commons}}
*[http://ryutao.main.jp/english/st2k_ngc2403.html Spiral Galaxy NGC 2403] at the astro-photography site of Mr. Takayuki Yoshida
*[https://web.archive.org/web/20070930031507/http://www.spacetelescope.org/bin/images.pl?searchtype=freesearch&string=2403 NGC 2403] at ESA/Hubble
*{{WikiSky}}
*{{APOD |date=19 February 2016 |title=NGC 2403}}
* [http://messier.seds.org/xtra/ngc/n2403.html SEDS] – NGC 2403

{{Sky|07|36|51.298|+|65|36|09.662|1000000}}
{{Catalogs|NGC=2403|C=7|UGC=3918|PGC=21396}}
{{Caldwell catalogue}}
{{Ngc25}}
{{Camelopardalis}}

[[Category:Intermediate spiral galaxies]]
[[Category:M81 Group]]
[[Category:Camelopardalis]]
[[Category:NGC objects|2403]]
[[Category:UGC objects|03918]]
[[Category:Principal Galaxies Catalogue objects|021396]]
[[Category:Caldwell objects|007b]]
[[Category:Astronomical objects discovered in 1788|17881101]]
[[Category:Discoveries by William Herschel]]
[[Category:MCG objects|+11-10-007 ]]
[[Category:IRAS catalogue objects|07321+6543]]