Editing Sagittarius (constellation) (section)

=== Deep-sky objects ===
[[File:Large Sagittarius star cloud.jpg|thumb|Large Sagittarius Star Cloud with Lagoon Nebula at top]]
[[File:Omega Nebula.jpg|thumbnail|right|250px|The Omega Nebula, also known as the Horseshoe or Swan Nebula]]
The [[Milky Way]] is at its densest near Sagittarius, as this is where the [[Galactic Center]] lies. As a result, Sagittarius contains many [[star cluster]]s and [[nebula]]e.

==== Star clouds ====
Sagittarius contains two well-known [[star cloud]]s, both considered fine binocular objects.
* The [[Large Sagittarius Star Cloud]] is the brightest visible region of the Milky Way. It is a portion of the central bulge of the galaxy seen around the thick dust of the [[Great Rift (astronomy)|Great Rift]], and is the innermost galactic structure that can be observed in visible wavelengths. It has several embedded clusters and superimposed dark nebulae.<ref>{{Cite journal |last=Crossen |first=Craig |date=July 2013 |title=Observing the Milky Way, part I: Sagittarius & Scorpius |journal=Sky & Telescope |volume=126 |issue=1 |language=en|page=24|bibcode=2013S&T...126a..24C }}</ref>
* The [[Small Sagittarius Star Cloud]], also known as Messier 24, has an apparent magnitude of 2.5. The cloud fills a space of significant volume to a depth of 10,000 to 16,000 light-years. Embedded in M24 is [[NGC 6603]], a small star cluster that is very dense. [[NGC 6567]], a dim [[planetary nebula]], and [[Barnard 92]], a [[Bok globule]], are also nearby.{{sfn|Levy|2005|pp=143–144}}

==== Nebulae ====
Sagittarius contains several well-known nebulae, including the [[Lagoon Nebula]] (Messier 8), near λ Sagittarii; the [[Omega Nebula]] (Messier 17), near the border with [[Scutum (constellation)|Scutum]]; and the [[Trifid Nebula]] (Messier 20), a large nebula containing some very young, hot stars.
* The [[Lagoon Nebula]] (M8) is an emission nebula that is located 5,000 light-years from Earth and measures 140 light-years by 60 light-years ([[celestial sphere|1.5°]]). Though it appears grey in telescopes to the unaided eye, long-exposure photographs reveal its pink hue, common to emission nebulae.<ref name="Wilkins Dunn 2006" /> It is fairly bright, with an integrated magnitude of 3.0.{{sfn|Levy|2005|p=108}} The Lagoon Nebula was discovered independently by [[John Flamsteed]] in 1680,{{sfn|Levy|2005|p=109}} [[Guillaume Le Gentil]] in 1747,<ref name="Wilkins Dunn 2006" /> and [[Charles Messier]] in 1764.{{sfn|Levy|2005|p=109}} The central area of the Lagoon Nebula is also known as the Hourglass Nebula, so named for its distinctive shape. The Hourglass Nebula has its shape because of matter propelled by [[Herschel 36]]. The Lagoon Nebula also features three [[dark nebula]]e listed in the [[Barnard Catalogue]].<ref name="Wilkins Dunn 2006" /> The Lagoon Nebula was instrumental in the discovery of [[Bok globules]], as [[Bart Bok]] studied prints of the nebula intensively in 1947. Approximately 17,000 Bok globules were discovered in the nebula nine years later as a part of the [[Palomar Sky Survey]]; studies later showed that Bok's hypothesis that the globules held [[protostar]]s was correct.{{sfn|Levy|2005|pp=111–112}}
* The [[Omega Nebula]] is a fairly bright nebula, sometimes called the Horseshoe Nebula or Swan Nebula.  It has an integrated magnitude of 6.0 and is 4890 light-years from Earth. It was discovered in 1746 by [[Jean-Philippe de Cheseaux|Philippe Loys de Chésaux]]; observers since him have differed greatly in how they view the nebula, hence its myriad of names. Most often viewed as a checkmark, it was seen as a swan by [[George Frederick Chambers|George F. Chambers]] in 1889, a loon by [[Roy Bishop]], and as a curl of smoke by [[Camille Flammarion]].{{sfn|Levy|2005|p=103}}
* The [[Trifid Nebula]] (M20, NGC 6514) is an emission nebula in Sagittarius that lies less than two degrees from the Lagoon Nebula. Discovered by French comet-hunter [[Charles Messier]], it is located between 2,000 and 9,000 light-years from Earth and has a diameter of approximately 50 light-years. The outside of the Trifid Nebula is a bluish [[reflection nebula]]; the interior is pink with two dark bands that divide it into three areas, sometimes called "lobes". Hydrogen in the nebula is ionized, creating its characteristic color, by a central triple star, which formed in the intersection of the two dark bands.<ref name="Wilkins Dunn 2006" /> M20 is associated with a cluster that has a magnitude of 6.3.{{sfn|Levy|2005|p=114}}
* The [[Red Spider Nebula]] (NGC 6537) is a planetary nebula located at a distance of about 4000 light-years from Earth.
* [[NGC 6559]] is a star-forming region located at a distance of about 5000 light-years from Earth, in the constellation of Sagittarius, showing both emission (red) and reflection (blue) regions.

In addition, several other nebulae have been located within Sagittarius and are of interest to astronomy.
* [[NGC 6445]] is a [[planetary nebula]] with an approximate magnitude of 11. A large nebula at over one [[arcminute]] in diameter, it appears very close to the [[globular cluster]] [[NGC 6440]].{{sfn|Levy|2005|p=133}}
* [[NGC 6638]] is a dimmer globular at magnitude 9.2, though it is more distant than M71 at a distance of 26,000 light-years. It is a Shapley class VI cluster; the classification means that it has an intermediate concentration at its core. It is approximately a degree away from the brighter globulars [[Messier 22|M22]] and [[Messier 28|M28]]; NGC 6638 is southeast and southwest of the clusters respectively.{{sfn|Levy|2005|pp=167–168}}

==== Other deep sky objects ====
[[File:Messier 54 HST.jpg|thumb|[[Messier 54]] was the first globular cluster found that is outside the Milky Way.<ref name="spacetelescope" /> ]]

In 1999 a violent outburst at [[V4641 Sagittarii|V4641 Sgr]] was thought to have revealed the location of the closest known black hole to Earth,<ref name="nrao" /> but later investigation increased its estimated distance by a factor of 15.<ref name="SAX" /> The complex radio source [[Sagittarius A]] is also in Sagittarius, near its western boundary with [[Ophiuchus]]. Astronomers believe that one of its components, known as [[Sagittarius A*]], is associated with a [[supermassive black hole]] at the [[Galactic Center|center of the galaxy]], with a mass of 2.6 million [[solar mass]]es.{{sfn|Levy|2005|p=143}} Although not visible to the naked eye, Sagittarius A* is located off the top of the spout of the Teapot asterism.<ref name="McClure2019" /> The [[Sagittarius Dwarf Elliptical Galaxy]] is located just outside the [[Milky Way]].

[[Baade's Window]] is an area with very little [[dust lane|obscuring dust]] that shows objects closer to the Milky Way's center than would normally be visible. [[NGC 6522]], magnitude 8.6, and [[NGC 6528]], magnitude 9.5, are both globular clusters visible through Baade's Window. 20,000 and 24,000 light-years from Earth, with Shapley classes of VI and V respectively, both are moderately concentrated at their cores. NGC 6528 is closer to the galactic core at an approximate distance of 2,000 light-years.{{sfn|Levy|2005|pp=174–175}}

[[2MASS-GC02]], also known as '''Hurt 2''', is a [[globular cluster]] at a distance of about 16 thousand [[light-year]]s from [[Earth]]. It was discovered in 2000 by Joselino Vasquez, and confirmed by a team of astronomers under the leadership of R. J. Hurt at [[2MASS]].<ref>{{cite web|title=2MASS-GC02, Hurt 2|url=http://spider.seds.org/spider/MWGC/2mass-gc02.html|access-date=15 January 2016}}</ref>