Sagittarius (constellation)

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Sagittarius

Constellation
List of stars in Sagittarius
Abbreviation	Sgr
Genitive	Sagittarii
Pronunciation	/ˌsædʒɨˈtɛəriəs/, genitive /ˌsædʒɨˈtɛəri.aɪ/
Symbolism	the Archer
Right ascension	19 h
Declination	−25°
Quadrant	SQ4
Area	867 sq. deg. (15th)
Main stars	12, 8
Bayer/Flamsteed stars	68
Stars with planets	24
Stars brighter than 3.00m	7
Stars within 10.00 pc (32.62 ly)	2
Brightest star	ε Sgr (Kaus Australis) (1.79m)
Nearest star	Ross 154 (9.69 ly, 2.97 pc)
Messier objects	15
Bordering constellations	Aquila Scutum Serpens Cauda Ophiuchus Scorpius Corona Australis Telescopium Indus (corner) Microscopium Capricornus
Visible at latitudes between +55° and −90°. Best visible at 21:00 (9 p.m.) during the month of August.

Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is (Unicode U+2650 ♐), a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow. It lies between Ophiuchus to the west and Capricornus to the east.

Visualizations

The constellation Sagittarius as it can be seen with the naked eye.

The constellation's brighter stars (from left to right on the map: τ, ζ, σ, φ, λ, ε, δ, and γ² Sagittarii) form an easily recognizable asterism known as 'the Teapot'. The stars δ Sgr (Kaus Media), ε Sgr (Kaus Australis), ζ Sgr (Ascella), and φ Sgr form the body of the pot; λ Sgr (Kaus Borealis) is the point of the lid; γ² Sgr (Alnasl) is the tip of the spout; and σ Sgr (Nunki) and τ Sgr the handle.^[1][2]

The constellation as a whole is often depicted as having the rough appearance of a stick-figure archer drawing its bow, with the fainter stars providing its horse body.

Notable features

Stars

The Teapot asterism in Sagittarius.

α Sgr (Rukbat) is not the brightest star of the constellation, having a magnitude of only 3.96 (not shown on the main map as it is located below the map's southeastern corner, north is up).

With 22 stars in this constellation known to have planets, Sagittarius has more known planetary host stars than any other constellation.

Deep-sky objects

An image showing Sagittarius.

The Milky Way is at its densest near Sagittarius, as this is where the galactic center lies. Consequently, Sagittarius contains many star clusters and nebulae. One of the brightest of the star clusters is Messier 55, about 7.5° west of δ Sgr.

The constellation contains nebulae such as the Lagoon Nebula (Messier 8), near λ Sagittarii, the Omega Nebula (Messier 17), also known as the Swan or Horseshoe Nebula, near the border with Scutum; and the Trifid Nebula (Messier 20), a large nebula containing some very young, hot stars. The grouping of the Lagoon Nebula, the Trifid Nebula, and NGC 6559 is often called the Sagittarius triplet.

Messier 54 was the first globular cluster found that is outside the Milky Way.^[3]

The Lagoon Nebula (M8) is an emission nebula discovered by Guillaume Le Gentil in 1747 that is located 5,000 light-years from Earth and measures 140 light-years by 60 light-years (1.5°). Though it appears grey in telescopes to the unaided eye, long-exposure photographs reveal its pink hue, common to emission nebulae. 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 nebulae catalogued in Barnard's Catalog.^[4]

The Trifid Nebula (M20) 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.^[4]

In 1999 a violent outburst at V4641 Sgr was thought to have revealed the location of the closest known black hole to Earth,^[5] but later investigation increased its estimated distance by a factor of 15.^[6] The complex radio source Sagittarius A is also here. Astronomers believe that one of its components, known as Sagittarius A*, is associated with a supermassive black hole at the center of the galaxy. The Sagittarius Dwarf Elliptical Galaxy is located just outside the Milky Way.

Mythology

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Sagittarius as depicted in Urania's Mirror, a set of constellation cards published in London c.1825.

The Babylonians identified Sagittarius as the god Nerigal or Nergal, a strange centaur-like creature firing an arrow from a bow.^[7] It is generally depicted with wings, with two heads, one panther head and one human head, as well as a scorpion's stinger raised above its more conventional horse's tail. The Sumerian name Pabilsag is composed of two elements - Pabil, meaning 'elder paternal kinsman' and Sag, meaning 'chief, head'. The name may thus be translated as the 'Forefather' or 'Chief Ancestor'.^[8] The figure is reminiscent of modern depictions of Sagittarius.

In Greek mythology, Sagittarius is identified as a centaur: half human, half horse. In some legends, the Centaur Chiron was the son of Philyra and Saturn, who was said to have changed himself into a horse to escape his jealous wife, Rhea. Chiron was eventually immortalised in the constellation of Centaurus or in some version, Sagittarius.^{[citation needed]}

The arrow of this constellation points towards the star Antares, the "heart of the scorpion."

Astrology

As of 2002, the Sun appears in the constellation Sagittarius from December 18 to January 18. In tropical astrology, the Sun is considered to be in the sign Sagittarius from November 22 to December 21, and in sidereal astrology, from December 16 to January 14.