Editing Magellanic Clouds (section)

== Characteristics ==
The [[Large Magellanic Cloud]] and its neighbour and relative, the [[Small Magellanic Cloud]], are conspicuous objects in the southern hemisphere, looking like separated pieces of the [[Milky Way]] to the naked eye. Roughly 21[[degree (angle)|°]] apart in the night sky, the true distance between them is roughly 75,000 [[light-years]]. Until the discovery of the [[Sagittarius Dwarf Elliptical Galaxy]] in 1994, they were the closest known galaxies to our own. The LMC lies about 160,000 light years away,<ref>{{cite journal |url=http://www.eso.org/public/news/eso1021/ |title=A Cosmic Zoo in the Large Magellanic Cloud |journal=European Southern Observatory Press Release |pages=21 |date=1 June 2010 |publisher=[[European Southern Observatory]] |access-date=29 August 2010|bibcode=2010eso..pres...21. }}</ref><ref name="Macrietal2006" >{{cite journal |last=Macri |first=L. M. |display-authors=etal |date=2006 |title=A New Cepheid Distance to the Maser-Host Galaxy NGC 4258 and Its Implications for the Hubble Constant |journal=The Astrophysical Journal |volume=652 |issue=2 |pages=1133–1149 |doi=10.1086/508530 |bibcode=2006ApJ...652.1133M|arxiv = astro-ph/0608211 |s2cid=15728812 }}</ref><ref name=freedman2010>Freedman, Wendy L.; Madore, Barry F. [http://adsabs.harvard.edu/abs/2010ARA%26A..48..673F "The Hubble Constant"], ''Annual Review of Astronomy and Astrophysics'', 2010</ref><ref name=majaess2010>Majaess, Daniel J.; Turner, David G.; Lane, David J.; Henden, Arne; Krajci, Tom [http://adsabs.harvard.edu/abs/2010arXiv1007.2300M "Anchoring the Universal Distance Scale via a Wesenheit Template"], ''Journal of the American Association of Variable Star Observers'', 2010</ref> while the SMC is around 200,000.<ref>{{cite web |url=http://www.spitzer.caltech.edu/images/2875-ssc2010-02a1-Little-Galaxy-Explored |title=Little Galaxy Explored |date=5 January 2010 |publisher=Jet Propulsion Laboratory, California Institute of Technology |access-date=29 August 2010}}</ref> The LMC is about 70% larger than the diameter of the SMC (32,200&nbsp;ly and 18,900&nbsp;ly respectively). For comparison, the Milky Way is about 87,400&nbsp;ly across.

The total mass of these two galaxies is uncertain. Only a fraction of their gas seems to have coalesced into stars and they probably both have large dark matter halos. One recent estimate of the total mass of the LMC is about 1/10 that of the Milky Way. That would make the LMC rather a large galaxy in the current observable universe. Since the sizes of relatively nearby galaxies are highly skewed, the average mass can be a misleading statistic. In terms of rank, the LMC appears to be the fourth most massive member of over 50 galaxies in the local group. Suggesting that the Magellanic cloud system is historically not a part of the Milky Way is evidence that the SMC has been in orbit about the LMC for a very long time. The Magellanic system seems most similar to the distinct [[NGC 3109]] system, which is on the edge of the Local Group.

Astronomers have long assumed that the Magellanic Clouds have orbited the Milky Way at approximately their current distances, but evidence suggests that it is rare for them to come as close to the Milky Way as they are now.<ref>{{cite journal|last=Ferris|first=Timothy|title=Dancing in the Dark|journal=[[National Geographic (magazine)|National Geographic]]| date=December 2011 |volume=220|issue=6|pages=118}}</ref> Observation and theoretical evidence suggest that the Magellanic Clouds have both been greatly distorted by [[tidal force|tidal]] interaction with the Milky Way as they travel close to it. The LMC maintains a very clear spiral structure in radio-telescope images of neutral hydrogen. Streams of neutral hydrogen connect them to the Milky Way and to each other, and both resemble disrupted [[barred spiral galaxy|barred spiral galaxies]].<ref>{{Cite web|url=http://www.aao.gov.au/images/captions/misc021.html|archiveurl=https://web.archive.org/web/20050715231207/http://www.aao.gov.au/images/captions/misc021.html|url-status=dead|title=The Large and Small Magellanic Clouds|archivedate=July 15, 2005|website=www.mq.edu.au}}</ref> Their [[gravity]] has affected the Milky Way as well, distorting the outer parts of the [[galactic disk]].

Aside from their different structure and lower mass, they differ from our galaxy in two major ways. They are gas-rich; a higher fraction of their mass is hydrogen and [[helium]] compared to the Milky Way.<ref>[http://home.insightbb.com/~lasweb/lessons/magellanic.htm http://home.insightbb.com/~lasweb/lessons/magellanic.htm] ''Home.insightbb.com'' Retrieved on 2007-05-31</ref> They are also more metal-poor than the Milky Way; the youngest [[star]]s in the LMC and SMC have a [[metallicity]] of 0.5 and 0.25 times solar, respectively.<ref>[http://aa.springer.de/papers/8336003/2300925/sc6.htm http://aa.springer.de/papers/8336003/2300925/sc6.htm] {{Webarchive|url=https://web.archive.org/web/20070607141837/http://aa.springer.de/papers/8336003/2300925/sc6.htm |date=2007-06-07 }} ''Aa.springer.de'' Retrieved on 2007-05-31</ref>  Both are noted for their [[nebula]]e and young [[stellar population]]s, but as in our own galaxy their stars range from the very young to the very old, indicating a long [[star formation|stellar formation]] history.<ref>Chaisson and McMillan</ref>

The Large Magellanic Cloud was the host galaxy to a [[supernova]] ([[SN 1987A]]), the brightest observed in over four centuries.

Measurements with the Hubble Space Telescope, announced in 2006, suggest the Magellanic Clouds may be moving too fast to be long term companions of the [[Milky Way]].<ref>{{cite web|title=Press release: Magellanic Clouds May Be Just Passing Through|url=https://www.cfa.harvard.edu/news/2007-02|publisher=[[Harvard University]]|date=January 9, 2007}}</ref>  If they are in orbit, that orbit takes at least 4 billion years. They are possibly on a first approach and we are witnessing the start of a galactic merger that may overlap with the Milky Way's expected merger with the [[Andromeda Galaxy]] (and perhaps the [[Triangulum Galaxy]]) in the future.

In 2019, astronomers discovered the young star cluster [[Price-Whelan 1]] using [[Gaia (spacecraft)|''Gaia'']] data. The star cluster has a low [[metallicity]] and belongs to the leading arm of the Magellanic Clouds. The existence of this star cluster suggests that the leading arm of the Magellanic Clouds is 90,000 light-years away from the Milky Way—closer than previously thought.<ref>{{Cite web|url=https://www.cosmos.ESA.int/web/Gaia/iow_20200109|title=IoW_20200109 - Gaia - Cosmos|website=www.cosmos.esa.int|access-date=2020-01-09}}</ref>

<gallery widths="200px" heights="200px">
Image:large.mc.arp.750pix.jpg|The [[Large Magellanic Cloud]] (LMC).
Image:VISTA’s view of the Small Magellanic Cloud.jpg|[[Small Magellanic Cloud]] (SMC).
File:Smclmc-35deg-16ks8k-min20k-4550k-m19-s1-s8.png|LMC and SMC rendered from [[Gaia (spacecraft)|Gaia EDR3]] data with foreground stars removed
</gallery>