Aquarius

Figure 2. Aquarius Dwarf.

Aquarius (abbreviation: Aqr), the Water-bearer, is a large but quite faint southern constellation and the twelfth sign of the zodiac. It is surrounded by Pegasus, Equuleus, and Delphinus to the north, Aquila to the west, Capricornus so the southwest, Pisces Austrinus and Sculptor to the south, and Cetus to the east.

The stars Sadachbia (Gamma), Eta Aqr, Zeta Aqr, and Pi Aqr form a small Y-shaped asterism, called the Water Jar or Urn, thought to mark the Water-bearer's cup.

See below for details of the constellation's brightest stars and interesting deep sky objects.

R Aquarii

R Aquarii. Hubble Space Telescope image.

R Aquarii is a symbiotic star thought to consist of a white dwarf and a Mira variable in a binary system. At a distance of about 710 light-years it is one of the nearest symbiotic stars to the Sun. It has been suggested that the nebula around R Aquarii is the remains of nova-like outburst, which may have been observed by Japanese astronomers in 930 AD.

Aquarids

The Aquarids are either of two distinct meteor showers with a radiant in Aquarius. The Eta Aquarids are observed between about 28 April and 21 May, peaking around May 5 or 6. This is a fine southern shower, associated with Halley's Comet. Typical meteor velocity is 67 kilometers per second (42 miles per second). The radiant is at RA 22h 20m, Dec –1°.

The Delta Aquarids occur between 14 July and 18 August, peaking on 29 July and 7 August. Meteor velocity is about 42 kilometers per second (26 miles per second). The radiant is double, the two components lying at RA 22h 36m, Dec –17° and RA 23h 04m, Dec +2°.

Aquarius Dwarf

The Aquarius Dwarf is an irregular galaxy (type ImV) and member of the Local Group. It lies about 3.2 million light-years from the Milky Way Galaxy in Aquarius (RA 20h 47m, Dec –12° 51'). It was first catalogued in 1959 by the DDO survey.

Although the Aquarius Dwarf contains significant amounts of neutral hydrogen – the raw material needed to make new stars – it displays a very low level of star formation, which results in it being one of the least luminous members of the Local Group Local Group. It has been conjectured that this is connected to its spatial isolation.

Stars in Aquarius brighter than magnitude 4.0
star	vis mag	abs mag.	spec type	distance (ly)	RA (h m s)	Dec (° ' ")
Beta (Sadalsuud)	2.90	-3.47	G0Ib	612	21 31 33	-05 34 16
Alpha (Sadalmelik)	2.95	-3.88	G2Ib	759	22 05 47	-00 19 11
Delta (Skat)	3.27	-0.18	A3V	159	22 54 39	-15 49 15
Zeta	3.65	1.14	F6IV+F3V	103	22 28 50	-00 01 12
c²	3.68	-0.60	K1III	234	23 09 27	-21 10 21
Lambda	3.73	-1.67	M2.5IIIaFe	392	22 52 37	-07 34 47
Epsilon (Albali)	3.78	-0.46	A1V	230	20 47 40	-09 29 45
Gamma (Sadachbia)	3.86	0.43	A0V	158	22 21 39	-01 23 14
b¹	3.96	0.48	K0III	162	23 22 58	-20 06 02

Other objects of interest
name	type of object	notes
V1344 Aqr	star	An X-ray jet variable
Helix Nebula	planetary nebula	NGC 7293. See separate entry
Saturn Nebula	planetary nebula	NGC 7009. See separate
M2 (NGC 7089)	globular cluster	On of the most impressive of its type; it appears in binoculars as a misty patch with a central concentration, and with a 15-cm telescope is partially resolved into stars. Magnitude 6.5, diameter 12.9', distance 37,500 light-years; RA 21h 31m, Dec -01° 03'
M72 (NGC 6981)	globular cluster	A faint object in small telescopes. Magnitude 9.8, diameter 2', distance 55,400 light-years; RA 20h 52m, Dec -12° 39'
Atoms for Peace Galaxy	galaxy	NGC 7252. See separate entry