Sagittarius

Sagittarius (abbreviation: Sgr), the Archer (actually, a centaur with a bow), is a large constellation of the southern hemisphere and ninth of the zodiac. It lies north of Corona Australis, south of Aquila, east of Capricornus and west of Ophiuchus. In the center of the constellation lies the conspicuous asterism known as the Milk Dipper or the Teapot, with a spout (formed by the stars Gamma, Delta, and Epsilon Sag), a handle (Zeta, Sigma, Tau, and Phi Sag), and a lid (Lambda Sag).

Rich in star fields, star clusters, and nebulae, Sagittarius straddles the plane of the Milky Way. At its very edge, at the border with Ophiuchus and Scorpius, lies the center of the Milky Way Galaxy, about 30,000 light-years distant. See below for details of the constellation's brightest stars and interesting deep sky objects.

Sagittarius Dwarf Irregular Galaxy

The Sagittarius Dwarf Irregular Galaxy (SagDIG, Sag dIrr) is a dwarf irregular galaxy, discovered in 1977, that is a member of the Local Group of galaxies. It has a diameter of about 3,000 light-years and lies about 3,500 light-years away in Sagittarius at celestial coordinates RA 19h 30m, Dec –17° 42'.

Sagittarius Arm

The Sagittarius Arm, also known as the Sagittarius-Carina Arm, is one of the spiral arms of the Milky Way Galaxy. It lies between the Sun and the center of the Galaxy in the direction of the constellation of Sagittarius.

Stars in Sagittarius brighter than magnitude 4.0
star	vis mag	abs mag	spec type	distance (ly)	RA (h m s)	Dec (° ' ")
Epsilon (Kaus Australis)	1.79	-1.45	B9.5III	145	18 24 10	-34 23 05
Sigma (Nunki)	2.05	-2.14	B2.5V	224	18 55 16	-26 17 48
Zeta (Ascella)	2.60	0.41	A2III+A4IV	89	19 02 37	-29 52 49
Delta (Kaus Media)	2.72	-2.14	K3IIIa	306	18 21 00	-29 49 42
Lambda (Kaus Borealis)	2.82	0.94	K1IIIb	77	18 27 58	-25 25 18
Pi (Albaldah)	2.82	-2.77	F2II	440	19 09 46	-21 01 25
Gamma (Alnasl)	2.98	0.63	K0III	96	18 05 48	-30 25 26
Eta	3.10	-0.20	M2III	149	18 17 38	-36 45 42
Phi	3.17	-1.08	B8III	231	18 45 39	-26 59 27
Tau	3.32	0.48	K1III	120	19 06 56	-27 40 13
Xi-2	3.52	-1.77	G8II	372	18 57 44	-21 06 24
Omicron	3.76	0.61	K0III	139	19 04 41	-21 44 30
Mu (Polis)	3.84v	-8.15	BIape	8,150	18 13 46	-21 03 32
Rho-1	3.92	1.06	F0III	122	19 21 40	-17 50 50
Beta-1 (Arkab Prior)	3.96	-1.37	B9V	378	19 22 38	-44 27 32
Alpha (Rukbat)	3.96	0.37	B8v	170	19 23 53	-40 36 58

Other objects of interest
name	type of object	notes
W Sgr	star	A Cepheid variable. Magnitude range 4.4 to 5.0; period 7d 14h; RA 18h 5.0m, Dec -29° 35'
NGC 6818	planetary nebula	Irregular oval shape. Magnitude 10; diameter 0.3'; RA 19° 44'
Lagoon Nebula	diffuse nebula	M8. See separate entry
Omega Nebula	diffuse nebula	M17. See separate entry
Trifid Nebula	diffuse nebula	M20. See separate entry
M18 (NGC 6613)	open cluster	A loose scattering of about 20 stars over 0.2° best viewed with binoculars or a small telescope. Magnitude 6.9; diameter 9'; RA 18h 19.0m, Dec -17° 8'
M21 (NGC 6531)	open cluster	Easy to resolve with a tight central grouping. Magnitude 6.9; diameter 9'; R.A. 18h 19.0m, Dec. -17° 8'
M23 (NGC 6494)	open cluster	A large cluster spanning nearly 0.5o, excellent with binoculars and resolvable with a small telescope into about 100 stars. Magnitude 5.5; diameter 27'; RA 17h 56.8m, Dec -19° 1'
M25 (IC 14725)	open cluster	About 50 stars, the brightest of sixth magnitude; good binocular object. Magnitude 4.6; diameter 31'; RA 18h 31.6m, Dec -19° 15'
NGC 6530	open cluster	About 25 stars near the Lagoon Nebula, the brightest of seventh magnitude; another good binocular cluster. Magnitude 4.6; diameter 14'; RA 18h 4.8m, Dec -24° 20'
M24	star field	The Sagittarius Star Cloud, part of Milky Way. To naked eye, it appears as a foggy patch; large telescopes reveal a rich field of stars. Magnitude 4.6; diameter 90'; RA 18h 16.9m, Dec -18° 29'
M28 (NGC 6626)	globular cluster	Magnitude 6.9; diameter 11.0'; RA 18h 24.5m, Dec -24° 52'
M54 (NGC 6715)	globular cluster	Close to Zeta Sgr and lying within the Sagittarius Dwarf Elliptical Galaxy, it is so dense that it is can mistaken through binoculars for a star. Magnitude 7.7; diameter 9.1'; RA 18h 55.1m, Dec -30° 29'
M55 (NGC 6809)	globular cluster	A large but loose globular that can be viewed with binoculars. Magnitude 6.9; diameter 19.0'; RA 19h 19.0m, Dec -17° 8'
M69 (NGC 6637)	globular cluster	Magnitude 7.7; diameter 7.1'; RA 18h 31.4m, Dec -32° 21'
M70 (NGC 6681)	globular cluster	Magnitude 8.1; diameter 7.8'; RA 18h 43.2m, Dec -32° 18'
M75 (NGC 6864)	globular cluster	Magnitude 8.6; diameter 6.0'; RA 20h 06.1m, Dec -21° 55'
Sagittarius Dwarf Elliptical Galaxy	galaxy	See separate entry
Sagittarius A	galaxy	See separate entry