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{{short description|Minor spiral arm of the Milky Way Galaxy and one of its most pronounced arms}}
[[Image:Milky Way Arms ssc2008-10.svg|500px|right|thumb|Observed structure of the [[Milky Way]]'s spiral arms
The '''Carina–Sagittarius Arm''' (also known as the '''Sagittarius Arm''' or '''Sagittarius–Carina Arm''', labeled '''-I'''{{clarify|date=April 2023|reason=What is this "-I" label meant to indicate?}}) is generally thought to be a minor [[spiral arm]] of the [[Milky Way]] [[galaxy]].<ref name=Churchwell2009/> Each spiral arm is a long, diffuse curving streamer of [[star]]s that radiates from the [[
Steiman-Cameron2010">{{Cite journal | last1 = Steiman-Cameron | first1 = T. Y. | last2 = Wolfire | first2 = M. | last3 = Hollenbach | first3 = D. | title = Cobeand the Galactic Interstellar Medium: Geometry of the Spiral Arms from Fir Cooling Lines | journal = The Astrophysical Journal | volume = 722 | issue = 2 | pages = 1460 | year = 2010 | doi = 10.1088/0004-637X/722/2/1460| bibcode=2010ApJ...722.1460S| doi-access = free }}</ref>▼
The Milky Way is a [[barred spiral galaxy]], consisting of a central crossbar and bulge from which two major and several minor spiral arms radiate outwards.
▲The '''Carina–Sagittarius Arm''' (also known as '''Sagittarius Arm''' or '''Sagittarius–Carina Arm''', labeled ''-I'') is generally thought to be a minor [[spiral arm]] of the [[Milky Way]] [[galaxy]].<ref name=Churchwell2009/> Each spiral arm is a long, diffuse curving streamer of [[star]]s that radiates from the [[galactic center]]. These gigantic structures are often composed of billions of stars and thousands of gas clouds. The Carina–Sagittarius Arm is one of the most pronounced arms in our galaxy as a large number of [[HII region]]s, young stars and [[giant molecular cloud]]s are concentrated in it.<ref name="
▲Steiman-Cameron2010">{{Cite journal | last1 = Steiman-Cameron | first1 = T. Y. | last2 = Wolfire | first2 = M. | last3 = Hollenbach | first3 = D. | title = Cobeand the Galactic Interstellar Medium: Geometry of the Spiral Arms from Fir Cooling Lines | journal = The Astrophysical Journal | volume = 722 | issue = 2 | pages = 1460 | year = 2010 | doi = 10.1088/0004-637X/722/2/1460| bibcode=2010ApJ...722.1460S}}</ref>
The arm dissipates near its middle, shortly after reaching its maximal angle, viewed from the Solar System, from the Galactic Center of about 80°. Extending from the galaxy's central bar is the '''Sagittarius Arm''' (Sagittarius bar). Beyond the dissipated zone it is the '''Carina Arm'''.<ref name=Churchwell2009/>
▲The Milky Way is a [[barred spiral galaxy]], consisting of a central crossbar from which two major and several minor spiral arms radiate outwards. The Carina–Sagittarius Arm lies between two major spiral arms—[[Scutum–Centaurus Arm]] inside and the [[Perseus Arm]] outside.<ref name=Churchwell2009>{{cite journal|last=Churchwell|first=Ed|author2=Babler, Brian L. |author3=Meade, Marlin A. |title=The Spitzer/GLIMPSE Surveys: A New View of the Milky Way|journal=Publications of the Astronomical Society of the Pacific|year=2009|volume=121|pages=213–230|doi=10.1086/597811|url=http://www.astro.wisc.edu/sirtf/Churchwell_2009.pdf|format=pdf|bibcode=2009PASP..121..213C}}</ref> It is named for its proximity to the [[Sagittarius (constellation)|Sagittarius]] and [[Carina (constellation)|Carina]] constellations as seen in the [[night sky]] from Earth, in the direction of the [[galactic center]].
==Geometry==
A study was done with the measured parallaxes and motions of 10 regions in the Sagittarius arm where massive stars are formed. Data was gathered using the BeSSeL Survey with the [[Very Long Baseline Array|VLBA]], and the results were synthesized to discover the physical properties of these sections (called the Galactocentric azimuth, around −2 and 65 degrees). The results were that the spiral pitch angle of the arms is 7.3 [[Plus–minus sign|±]] 1.5 degrees, and the half-width of the arms of the Milky Way were found to be 0.2 kpc. The nearest part to the Sun is around 1.4 ± 0.2 kpc away.<ref>{{cite journal |last1=Wu |first1=Y. |last2=Sato |first2=M. |last3=Zheng |first3=X. |title=Trigonometric parallaxes of star forming regions in the Sagittarius spiral arm |journal=[[Astronomy & Astrophysics]] |year=2014 |volume=566 |pages=A17 |doi=10.1051/0004-6361/201322765 |display-authors=etal |arxiv=1404.4683 |bibcode=2014A&A...566A..17W |s2cid=118592025}}</ref>
==Minor arm==
In 2008, infrared observations with the [[Spitzer Space Telescope]] showed that the Carina–Sagittarius Arm has a relative paucity of young stars, in contrast with the [[Scutum-Centaurus Arm]] and [[Perseus Arm]]. This suggests that the Carina–Sagittarius Arm is a minor arm, along with the [[Norma Arm]] (Outer Arm). These two appear to be mostly concentrations of gas, sparsely sprinkled with pockets of newly formed stars.<ref name=Churchwell2009/><ref>{{cite news |first=David |last=Shiga
▲In 2008, infrared observations with the [[Spitzer Space Telescope]] showed that the Carina–Sagittarius Arm has a relative paucity of young stars, in contrast with the [[Scutum-Centaurus Arm]] and [[Perseus Arm]]. This suggests that the Carina–Sagittarius Arm is a minor arm, along with the [[Norma Arm]] (Outer Arm). These two appear to be mostly concentrations of gas, sparsely sprinkled with pockets of newly formed stars.<ref name=Churchwell2009/><ref>{{cite news |first=David |last=Shiga |authorlink= |title=Two of the Milky Way's spiral arms may be 'demoted' |url=https://www.newscientist.com/article/dn14057-two-of-the-milky-ways-spiral-arms-may-be-demoted.html |work=NewScientist |publisher= |date=2008-06-03 |accessdate=2009-09-08 }}</ref>
==Visible objects==
[[File:Milky Way Sagittarius Arm.jpg|
A number of [[Messier
*[[Wild Duck Cluster|M11, the Wild Duck Cluster]] in [[Scutum (constellation)|Scutum]] ([[Right ascension|RA]] 18h 51m)
*[[Lagoon Nebula|M8, the Lagoon Nebula]]▼
*[[
*[[Eagle Nebula|M16, the Eagle Nebula]] in [[Serpens]] (RA 18h 19m)
*[[Omega Nebula|M17, the Omega Nebula]] in Sagittarius (RA 18h 20.4m)
*[[Open Cluster M18]] in Sagittarius (RA 18h 19.9m)
*[[Globular Cluster M55]] in Sagittarius (RA 19h 40m)▼
*[[Small Sagittarius Star Cloud|M24, the Small Sagittarius Star Cloud]] (RA 18h 17m)
*[[
▲*[[Lagoon Nebula|M8, the Lagoon Nebula]] in Sagittarius (RA 18h 4m)
*[[Carina Nebula|NGC 3372, the Carina Nebula]] in Carina (RA 10h 45m)▼
▲*[[Globular Cluster M55]]
▲*[[Carina Nebula|NGC 3372, the Carina Nebula]]
==See also==
*[[Galactic disc]]
==References==
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{{Milky Way}}
{{Portal bar|Stars|Spaceflight|Outer space|Solar System}}
{{DEFAULTSORT:Carina-Sagittarius Arm}}
[[Category:Carina–Sagittarius Arm| ]]
[[Category:Milky Way arms]]
[[Category:Galactic astronomy]]
[[Category:Spiral galaxies]]
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