Aqr · Aquarii
Aquarius Constellation
IAU constellation mapAqrAquarius (Aqr) is one of the 88 constellations recognised by the International Astronomical Union. It covers 980 square degrees of the equatorial sky in quadrant SQ4. Its brightest star is Sadalsuud. The Latin genitive of the name is Aquarii, used to form star names within the constellation. In Greek mythology, Aquarius is associated with babylonian tradition. The IAU standardised all constellation boundaries in 1930.
Quick facts
- IAU name
- Aquarius
- Abbreviation
- Aqr
- Latin genitive
- Aquarii
- Hemisphere
- equatorial
- Area
- 980 sq deg
- Brightest star
- Sadalsuud
- Quadrant
- SQ4
- Family
- Zodiac
- Mythology origin
- Babylonian/Greek
- Discovery era
- Ptolemy's 48 (Almagest, c. 150 CE)
Mythology
Aquarius, the Water Bearer, is one of the oldest recognised constellations. In Babylonian astronomy (c. 2000 BCE) it was called GU.LA, identified with the god Ea, who was associated with wisdom and water; the figure was depicted pouring water from a vase, creating the 'great flood' of Babylonian cosmology. In Greek tradition the Water Bearer was variously identified with Deucalion, who survived the great flood sent by Zeus, or with Ganymede, the beautiful Trojan prince whom Zeus (in the form of an eagle) abducted to serve as cupbearer to the gods on Olympus. In some accounts Aquarius represents Cecrops, the first king of Athens, who poured water rather than wine in early religious sacrifices. The constellation lies in a region of sky sometimes called the 'Sea', a large area containing several water-related constellations including Pisces, Capricornus, and Piscis Austrinus. Sadalsuud (Beta Aquarii), the brightest star at magnitude 2.87, is a yellow supergiant about 610 light-years from Earth. The Helix Nebula (NGC 7293) in Aquarius is the closest planetary nebula to the Solar System, about 650 light-years away, and the largest apparent planetary nebula in the sky.
Sources: Aratus Phaenomena 283-299; Hyginus Astronomica 2.29; Apollodorus Bibliotheca 3.12.2.
Overview
Aquarius is one of the 88 constellations formally recognised by the International Astronomical Union (IAU). It occupies 980 square degrees of sky in the equatorial sky region, crossing both hemispheres, best visible at latitudes between +45 and -90 degrees in September. The constellation belongs to the Zodiac family of constellations. Its Latin genitive is Aquarii, the form used when naming stars within the constellation — for example, the brightest star Sadalsuud may appear in catalogues as Alpha Aquarii or similar. The IAU standardised the boundaries of all 88 constellations in 1930 under the direction of Eugène Delporte, using straight lines of right ascension and declination to eliminate the ambiguities of earlier variable-boundary systems.
Notable stars
The brightest star in Aquarius is Sadalsuud. Individual stars within Aquarius are conventionally named using Bayer designation — Greek letters followed by the Latin genitive of the constellation name (Aquarii) — introduced by Johann Bayer in his 1603 star atlas Uranometria. Flamsteed numbers (numeric designators followed by Aquarius) were added by John Flamsteed in his 1712 catalogue. Variable stars, double stars, and deep-sky objects within the Aquarius boundary are catalogued by the IAU with the abbreviation Aqr.
History and mythology
The figure of Aquarius appears in the classical astronomical tradition. Ptolemy included this constellation in the Almagest (c. 150 CE), the definitive ancient catalogue of 48 constellations, which formed the foundation for Islamic, medieval European, and Renaissance astronomy. The constellation's figure and mythology were transmitted through works such as Aratus's Phaenomena, Eratosthenes's Catasterismi, and Hyginus's Astronomica. See the Mythology section above for the full narrative.
Sources & further reading (2)
- official-iau — accessed 2026-05-06
- encyclopedia — accessed 2026-05-06
Frequently asked questions
What does the name Aquarius mean?
Aquarius is the Latin name used by the IAU to designate this constellation. The name comes from classical Latin and Greek astronomical tradition. In star catalogues, stars within Aquarius are designated using the genitive form of the name (e.g. Alpha Aquarius or similar Latin genitive forms) — a naming convention introduced by Johann Bayer in his 1603 atlas Uranometria and still in use today.
How large is Aquarius compared to other constellations?
Aquarius covers 980 square degrees of sky. The full sphere of the sky contains 41,253 square degrees, so Aquarius occupies about 2.4% of the total sky. For comparison, the largest constellation is Hydra at 1303 square degrees; the smallest is Crux at 68 square degrees.
When and where is Aquarius visible?
Aquarius straddles the celestial equator and is visible from both hemispheres, though part of it may be low on the horizon depending on the observer's latitude. The brightest star, Sadalsuud, serves as the main visual anchor for locating the constellation. As with all constellations, the best viewing conditions are a dark sky away from artificial light pollution, with the constellation high enough above the horizon to minimise atmospheric absorption.
