Ori · Orionis
Orion Constellation
IAU constellation mapOriOrion (Ori) is one of the 88 constellations recognised by the International Astronomical Union. It covers 594 square degrees of the equatorial sky in quadrant NQ1. Its brightest star is Rigel. The Latin genitive of the name is Orionis, used to form star names within the constellation. In Greek mythology, Orion is associated with greek tradition. The IAU standardised all constellation boundaries in 1930.
Quick facts
- IAU name
- Orion
- Abbreviation
- Ori
- Latin genitive
- Orionis
- Hemisphere
- equatorial
- Area
- 594 sq deg
- Brightest star
- Rigel
- Quadrant
- NQ1
- Family
- Orion
- Mythology origin
- Greek
- Discovery era
- Ptolemy's 48 (Almagest, c. 150 CE)
Mythology
Orion the Hunter is one of the most recognisable constellations in the sky, dominated by the asterism of three bright stars in a row (Alnitak, Alnilam, and Mintaka) that form Orion's Belt. In Greek mythology Orion was a giant huntsman of divine parentage — son of Poseidon according to most accounts — famed for his beauty and his prowess as a hunter. His death has several contradictory accounts: Artemis killed him, either because Apollo tricked her into shooting him, because Orion boasted he would kill all the animals on Earth (enraging Gaia who sent the Scorpion), or because he tried to assault Artemis herself. Orion's hunting dogs are the constellations Canis Major and Canis Minor; his prey includes Lepus the Hare. Rigel (Beta Orionis), the constellation's brightest star at magnitude 0.13, is a blue-white supergiant about 860 light-years from Earth and approximately 120,000 times more luminous than the Sun. Betelgeuse (Alpha Orionis) is a red supergiant in the late stages of stellar evolution, expected to explode as a supernova within the next million years or so. The Orion Nebula (Messier 42) is the nearest stellar nursery to Earth, about 1,344 light-years away, and easily visible to the naked eye as the 'fuzzy star' in Orion's Sword.
Sources: Aratus Phaenomena 323-335; Hesiod Works and Days 619-620; Apollodorus Bibliotheca 1.4.3.
Overview
Orion is one of the 88 constellations formally recognised by the International Astronomical Union (IAU). It occupies 594 square degrees of sky in the equatorial sky region, crossing both hemispheres, best visible at latitudes between +90 and -60 degrees in December. The constellation belongs to the Orion family of constellations. Its Latin genitive is Orionis, the form used when naming stars within the constellation — for example, the brightest star Rigel may appear in catalogues as Alpha Orionis 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 Orion is Rigel. Individual stars within Orion are conventionally named using Bayer designation — Greek letters followed by the Latin genitive of the constellation name (Orionis) — introduced by Johann Bayer in his 1603 star atlas Uranometria. Flamsteed numbers (numeric designators followed by Orion) were added by John Flamsteed in his 1712 catalogue. Variable stars, double stars, and deep-sky objects within the Orion boundary are catalogued by the IAU with the abbreviation Ori.
History and mythology
The figure of Orion 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 Orion mean?
Orion 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 Orion are designated using the genitive form of the name (e.g. Alpha Orion 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 Orion compared to other constellations?
Orion covers 594 square degrees of sky. The full sphere of the sky contains 41,253 square degrees, so Orion occupies about 1.4% 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 Orion visible?
Orion 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, Rigel, 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.
