Editing Small Magellanic Cloud (section)

==Observation history==
[[File:Panoramic Large and Small Magellanic Clouds.jpg|thumb|left|Panoramic Large and Small Magellanic Clouds as seen from [[ESO]]'s [[Very Large Telescope|VLT]] observation site. The galaxies are on the left side of the image.]]
[[File:Tucana IAU.svg|thumb|left|Constellation of [[Tucana]]: the SMC is the green shape at the south (bottom) of the picture]]
In the southern hemisphere, the Magellanic clouds have long been included in the lore of native inhabitants, including [[Pacific Ocean|south sea]] islanders and [[indigenous Australians]]. [[Persia]]n astronomer [[Abd Al-Rahman Al Sufi|Al Sufi]] mentions them in his ''[[Book of Fixed Stars]]'', repeating a quote by the [[polymath]] [[Ibn Qutaybah]], but had not observed them himself. [[Europe]]an sailors may have first noticed the clouds during the [[Middle Ages]] when they were used for navigation. [[Kingdom of Portugal|Portuguese]] and [[Dutch Republic|Dutch]] sailors called them the Cape Clouds, a name that was retained for several centuries. During the circumnavigation of the Earth by [[Ferdinand Magellan]] in 1519&ndash;1522, they were described by [[Antonio Pigafetta]] as dim clusters of stars.<ref>{{cite book
 | first=Bengt E. | last=Westerlund | date=1997
 | title=The Magellanic Clouds
 | publisher=Cambridge University Press
 | isbn=978-0-521-48070-3 }}</ref> In [[Johann Bayer]]'s celestial atlas ''[[Uranometria]]'', published in 1603, he named the smaller cloud, Nubecula Minor.<ref>{{cite book
 | first=Stephen James | last=O'Meara | date=2002
 | title=The Caldwell Objects
 | publisher=Cambridge University Press
 | isbn=978-0-521-82796-6 }}</ref> In [[Latin]], Nubecula means a little cloud.<ref>{{cite book
 | first=Charlton Thomas | last=Lewis | date=1918
 |author2=Kingery, Hugh Macmaster
  | title=An elementary Latin dictionary
 | url=https://archive.org/details/bub_gb_2ncKAAAAIAAJ | publisher=American Book Company
 | isbn=978-0-19-910205-1 }}</ref>
[[File:Small_Magellanic_Cloud.png|thumb|left|Small Magellanic Cloud as photographed by an [[amateur astronomy|amateur astronomer]]. Unrelated stars have been edited out.]]

Between 1834 and 1838, [[John Frederick William Herschel]] made observations of the southern skies with his {{convert|14|in|cm|adj=on}} reflector from the [[Royal Observatory, Cape of Good Hope|Royal Observatory]]. While observing the Nubecula Minor, he described it as a cloudy mass of light with an oval shape and a bright center. Within the area of this cloud, he catalogued a concentration of 37 nebulae and clusters.<ref>{{cite book
 | first=John Frederick William | last=Herschel
 | date=1849 | title=Outlines of Astronomy
 | publisher=Lea & Blanchard
 | location=Philadelphia
 | isbn=978-0-665-18744-5 }}</ref>

In 1891, [[Harvard College Observatory]] opened an observing station at [[Arequipa Region|Arequipa]] in [[Peru]]. Between 1893 and 1906, under the direction of [[Solon Irving Bailey|Solon Bailey]], the {{convert|24|in|mm|adj=on}} telescope at this site was used to survey photographically both the Large and Small Magellanic Clouds.<ref>{{cite book
 | first=Malcolm S. | last=Longair | date=2006
 | title=The Cosmic Century: A History of Astrophysics and Cosmology
 | url=https://archive.org/details/cosmiccenturyhis0000long | url-access=registration | publisher=Cambridge University Press
 | isbn=978-0-521-47436-8 }}</ref> [[Henrietta Swan Leavitt]], an astronomer at the [[Harvard College Observatory]], used the plates from Arequipa to study the variations in relative luminosity of stars in the SMC. In 1908, the results of her study were published, which showed that a type of [[variable star]] called a "cluster variable", later called a [[Cepheid variable]] after the prototype star [[Delta Cephei]], showed a definite relationship between the variability period and the star's apparent brightness. Leavitt realized that since all the stars in the SMC are roughly the same distance from Earth, this result implied a similar relationship between period and absolute brightness.<ref>{{cite journal
 | last=Leavitt | first=Henrietta S.
 | title=1777 variables in the Magellanic Clouds
 | journal=Annals of Harvard College Observatory
 | date=1908 | volume=60 | pages=87&ndash;108
 | bibcode=1907AnHar..60...87L }}</ref> This important [[period-luminosity relation]] allowed the distance to any other Cepheid variable to be estimated in terms of the distance to the SMC.<ref>{{cite book
 | first=Antonio | last=Aparicio
 |author2=Herrero, Artemio |author3=Sánchez, Francisco
  | date=1998 | title=Stellar Astrophysics for the Local Group
 | publisher=Cambridge University Press | isbn=978-0-521-56327-7 }}</ref> She hoped a few Cepheid variables could be found close enough to Earth so that their [[parallax]], and hence distance from Earth, could be measured. This soon happened, allowing Cepheid variables to be used as [[standard candle]]s, facilitating many astronomical discoveries.<ref name=PLhistory>{{cite journal |last=Fernie |first=J.D. |title=The Period–Luminosity Relation: A Historical Review |journal=Publications of the Astronomical Society of the Pacific |date=December 1969 |volume=81 |issue=483 |page=707 |bibcode=1969PASP...81..707F |doi=10.1086/128847|doi-access=free }}</ref>

Using this period-luminosity relation, in 1913, the distance to the SMC was first estimated by [[Ejnar Hertzsprung]]. First, he measured thirteen nearby cepheid variables to find the [[absolute magnitude]] of a variable with a period of one day. By comparing this to the periodicity of the variables as measured by Leavitt, he was able to estimate a distance of 10,000 parsecs (30,000 light years) between the Sun and the SMC.<ref>{{cite book | first=John R. | last=Gribbin | date=1999 | title=The Birth of Time: How Astronomers Measured the Age of the Universe | publisher=Yale University Press | isbn=978-0-300-08346-0 | url-access=registration | url=https://archive.org/details/birthoftimehowas00grib }}</ref> This later proved to be a gross underestimate of the true distance, but it did demonstrate the potential usefulness of this technique.<ref>{{cite journal
 | last=Hoffleit | first=Dorrit
 | title=The Selector of Highlights: A Brief Biographical Sketch of Harlow Shapley
 | journal=The Journal of the American Association of Variable Star Observers
 | date=1992 | volume=21 | issue=2 | pages=151–156
 | bibcode=1992JAVSO..21..151H }}</ref>

Announced in 2006, measurements with the [[Hubble Space Telescope]] suggest that either the Large and Small Magellanic Clouds may be moving too fast to be orbiting the [[Milky Way]], or that the Milky Way Galaxy is more massive than was thought.<ref>{{cite web|title=Press release: Magellanic Clouds May Be Just Passing Through|url=https://www.cfa.harvard.edu/news/just-passing-through|publisher=Harvard University|date=January 9, 2007}}</ref>