Editing Canis Major (section)

=== Deep-sky objects ===
The band of the [[Milky Way]] goes through Canis Major, with only patchy obscurement by [[interstellar dust]] clouds. It is bright in the northeastern corner of the constellation, as well as in a triangular area between Adhara, Wezen and Aludra, with many stars visible in binoculars. Canis Major boasts several [[open cluster]]s.<ref name="crossen 2004">{{cite book|author1=Crossen, Craig |author2=Rhemann, Gerald |title=Sky Vistas: Astronomy for Binoculars and Richest-Field Telescopes|publisher=Springer|location=New York, New York|year=2004|pages=[https://archive.org/details/springer_10.1007-978-3-7091-0626-6/page/n139 113]–15|isbn=978-3-211-00851-5|url=https://archive.org/details/springer_10.1007-978-3-7091-0626-6|quote=Canis Major. }}</ref> The only [[Messier object]] is [[Messier 41|M41]] (NGC 2287), an open cluster with a combined [[visual magnitude]] of 4.5, around 2300 light-years from Earth. Located 4 degrees south of Sirius, it contains contrasting blue, yellow and orange stars and covers an area the apparent size of the [[full moon]]—in reality around 25 light-years in diameter.<ref name="kambic09">{{cite book|last=Kambic|first=Bojan |title=Viewing the Constellations with Binoculars: 250+ Wonderful Sky Objects to See and Explore|publisher=Springer|location=New York, New York|year=2009|pages=230–32|isbn=978-0-387-85355-0|url=https://books.google.com/books?id=3vxLNPNHOcwC&q=Sirius+%22M+41%22&pg=PA230}}</ref><!-- cites two previous sentences --> Its most luminous stars have already evolved into giants. The brightest is a 6.3-magnitude star of spectral type K3. Located in the field is [[12 Canis Majoris]], though this star is only 670 light-years distant.<ref>{{cite book|last=De Laet|first=Rony |title=The Casual Sky Observer's Guide: Stargazing with Binoculars and Small Telescopes|publisher=Springer|location=New York, New York|year=2011|pages=95–97|isbn=978-1-4614-0595-5|url=https://books.google.com/books?id=3fhBelJk-30C&pg=PA95}}</ref><!-- cites previous two sentences --> [[NGC 2360]], known as Caroline's Cluster after its discoverer [[Caroline Herschel]], is an open cluster located 3.5 degrees west of Muliphein and has a combined apparent magnitude of 7.2. Around 15 light-years in diameter, it is located 3700 light-years away from Earth,<ref name="o'meara">{{cite book |title=The Caldwell Objects |first=Stephen James |last=O'Meara |publisher=Cambridge University Press|location=Cambridge, United Kingdom |year=2002 |pages=231–33 | isbn=978-0-521-82796-6}}</ref> and has been dated to around 2.2&nbsp;billion years old.<ref name="Mermilliod">{{cite journal|author1=Mermilliod, Jean-Claude |author2=Mayor, Michel |year=1990|title= Red Giants in Open Clusters. III - Binarity and Stellar Evolution in Five Intermediate-age Clusters: NGC 2360, 2423, 5822, 6811, and IC 4756|journal=Astronomy and Astrophysics |volume=273|issue=1|pages= 61–72 |bibcode=1990A&A...237...61M}}</ref> [[NGC 2362]] is a small, compact open cluster, 5200 light-years from Earth. It contains about 60 stars, of which Tau Canis Majoris is the brightest member.{{sfn|Ridpath|Tirion|2001|pp=98–99}} Located around 3 degrees northeast of Wezen, it covers an area around 12 light-years in diameter, though the stars appear huddled around Tau when seen through binoculars. It is a very young open cluster as its member stars are only a few million years old.  Lying 2 degrees southwest of NGC 2362 is [[NGC 2354]] a fainter open cluster of magnitude 6.5, with around 15 member stars visible with binoculars.<ref name="kambic09"/><!-- cites previous three sentences --> Located around 30' northeast of NGC 2360,<ref>{{cite book|author=Thompson, Robert and Barbara|title=Illustrated Guide to Astronomical Wonders: From Novice to Master Observer|publisher=O'Reilly Media, Inc.|location=Sebastopol, California|year=2007|page=144|isbn=978-0-596-52685-6|url=https://books.google.com/books?id=ymt9nj_uPhwC&pg=PA144}}</ref> [[NGC 2359]] (Thor's Helmet or the Duck Nebula) is a relatively bright [[emission nebula]] in Canis Major, with an approximate magnitude of 10, which is 10,000 light-years from Earth. The nebula is shaped by [[HD 56925]], an unstable [[Wolf–Rayet star]] embedded within it.<ref>{{cite book |first = David H. |last = Levy |title = Deep Sky Objects |publisher = Prometheus Books |location = Amherst, New York |year = 2005 |isbn = 978-1-59102-361-6 |page = [https://archive.org/details/deepskyobjects00davi/page/108 108] |url = https://archive.org/details/deepskyobjects00davi/page/108 }}</ref>

[[File:Stars fleeing a cosmic crash.jpg|thumb|[[ESO 489-056]] is an irregular [[dwarf galaxy]], located 16 million light-years distant.<ref name="www.spacetelescope.org">{{cite news|title=Stars Fleeing a Cosmic Crash |url=http://www.spacetelescope.org/images/potw1332a/|access-date=14 August 2013|newspaper=ESA/Hubble Picture of the Week}}</ref> ]]

In 2003, an overdensity of stars in the region was announced to be the [[Canis Major Dwarf]], the closest [[satellite galaxy]] to Earth. However, there remains debate over whether it represents a disrupted dwarf galaxy or in fact a variation in the thin and thick disk and spiral arm populations of the Milky Way. Investigation of the area yielded only ten [[RR Lyrae variable]]s—consistent with the [[Milky Way halo|Milky Way's halo]] and thick disk populations rather than a separate dwarf spheroidal galaxy.<ref>{{cite journal|author1=Mateu, Cecilia |author2=Vivas, A. Katherina |author3=Zinn, Robert |author4=Miller, Lissa R. |author5=Abad, Carlos |year=2009|title=No Excess of RR Lyrae Stars in the Canis Major Overdensity|journal=The Astronomical Journal|volume=37|issue=5|pages=4412–23 |bibcode=2009AJ....137.4412M|doi=10.1088/0004-6256/137/5/4412|arxiv = 0903.0376 |s2cid=18967866 }}</ref> On the other hand, a [[globular cluster]] in Puppis, [[NGC 2298]]—which appears to be part of the Canis Major dwarf system—is extremely metal-poor, suggesting it did not arise from the Milky Way's thick disk, and instead is of extragalactic origin.<ref>{{cite book  | last = O'Meara  | first = Stephen James  | year = 2011  | title = Deep-Sky Companions: The Secret Deep | publisher = Cambridge University Press | location = Cambridge, United Kingdom  | isbn = 978-0-521-19876-9 |url=https://books.google.com/books?id=v859bKO0A4gC&q=Canis+Major&pg=PA140 |page=139}}</ref>

[[NGC 2207 and IC 2163]] are a pair of face-on [[interacting galaxy|interacting]] spiral galaxies located 125&nbsp;million light-years from Earth. About 40&nbsp;million years ago, the two galaxies had a close encounter and are now moving farther apart; nevertheless, the smaller IC 2163 will eventually be incorporated into NGC 2207. As the interaction continues, gas and dust will be perturbed, sparking extensive [[star formation]] in both galaxies.{{sfn|Wilkins|Dunn|2006|p=456}} Supernovae have been observed in NGC 2207 in 1975 (type Ia [[SN 1975a]]),<ref>{{cite journal|author1=Kirshner, Robert P. |author2=Arp, H.C. |author3=Dunlap, J.R. |year=1976|title=Observations of Supernovae – 1975a in NGC 2207 and 1975b in the Perseus Cluster|journal=Astrophysical Journal|volume=207|issue=1|pages=44–52|bibcode=1976ApJ...207...44K|doi=10.1086/154465|doi-access=free}}</ref> 1999 (the type Ib [[SN 1999ec]]),<ref>{{cite journal|author1=Jha, S. |author2=Garnavich, P. |author3=Challis, P. |author4=Kirshner, R. |author5=Berlind, P. |year=1999|title=Supernova 1999ec in NGC 2207|journal=IAU Circular|volume=7269|page=2|bibcode=1999IAUC.7269....2J}}</ref> 2003 (type 1b supernova [[SN 2003H]]),<ref>{{cite web | first=David | last=Bishop | title=Bright Supernovae – 2003 | publisher=Rochester University | url=http://www.rochesterastronomy.org/sn2003/ | access-date=7 March 2014}}</ref> and 2013 (type II supernova [[SN 2013ai]]).<ref>{{cite journal |last1=Alain |first1=Klotz |last2=E. |first2=Conseil |last3=M. |first3=Fraser |last4=Joseph |first4=Brimacombe |last5=C. |first5=Inserra |last6=N. |first6=Walton |last7=N. |first7=Blagorodnova |last8=M. |first8=Nicholl |last9=S. |first9=Benetti |last10=A. |first10=Pastorello |last11=S. |first11=Valenti |last12=S. |first12=Taubenberger |last13=J. |first13=Smartt S. |last14=K. |first14=Smith |last15=D. |first15=Young |last16=M. |first16=Sullivan |last17=A. |first17=Gal-Yam |last18=O. |first18=Yaron |title=Supernova 2013ai in NGC 2207 = Psn J06161835-2122329 |journal=Central Bureau Electronic Telegrams |date=2013 |volume=3431 |pages=1 |bibcode=2013CBET.3431....1K}}</ref> Located 16&nbsp;million light-years distant,<ref name="www.spacetelescope.org"/> [[ESO 489-056]] is an irregular [[dwarf galaxy|dwarf-]] and [[low-surface-brightness galaxy]] that has one of the lowest [[metallicity|metallicities]] known.<ref>{{cite journal|author1=Kunth, Daniel |author2=Östlin, Goran |date=2000|title=The Most Metal-poor Galaxies|journal=The Astronomy and Astrophysics Review|volume=10|issue=1–2|pages=1–79|bibcode=2000A&ARv..10....1K|doi=10.1007/s001590000005|arxiv = astro-ph/9911094 |s2cid=15487742 }}</ref>

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