Per · Persei
Perseus Constellation
IAU constellation mapPerPerseus (Per) is one of the 88 constellations recognised by the International Astronomical Union. It covers 615 square degrees of the northern sky in quadrant NQ1. Its brightest star is Mirfak. The Latin genitive of the name is Persei, used to form star names within the constellation. In Greek mythology, Perseus is associated with greek tradition. The IAU standardised all constellation boundaries in 1930.
Quick facts
- IAU name
- Perseus
- Abbreviation
- Per
- Latin genitive
- Persei
- Hemisphere
- northern
- Area
- 615 sq deg
- Brightest star
- Mirfak
- Quadrant
- NQ1
- Family
- Perseus
- Mythology origin
- Greek
- Discovery era
- Ptolemy's 48 (Almagest, c. 150 CE)
Mythology
Perseus, the hero who slew the Gorgon Medusa, is depicted in the sky holding the severed head of Medusa (represented by the star Algol, the 'Demon Star'). Perseus was the son of Zeus and Danae; he was tasked with bringing the head of Medusa, the mortal Gorgon whose gaze could turn onlookers to stone. Armed with winged sandals from Hermes, the reflective shield of Athena, and the cap of invisibility from Hades, he approached the sleeping Gorgons and beheaded Medusa without looking directly at her, using her reflection in the polished shield. On his return he rescued Andromeda from the sea monster Cetus. Algol (Beta Persei), historically called the 'Demon Star' or 'Ghoul Star' (from Arabic al-ghul), is an eclipsing binary star system with a period of about 2.87 days; as the dimmer companion passes in front of the brighter, Algol visibly fades from magnitude 2.1 to 3.4 over several hours — a variation familiar to naked-eye observers for millennia. The Perseus Double Cluster (NGC 869 and NGC 884) is a pair of open clusters visible to the naked eye and spectacular in binoculars, each containing hundreds of blue and white supergiant stars.
Sources: Apollodorus Bibliotheca 2.4.1-3; Ovid Metamorphoses 4.608-803; Hyginus Astronomica 2.12.
Overview
Perseus is one of the 88 constellations formally recognised by the International Astronomical Union (IAU). It occupies 615 square degrees of sky in the northern hemisphere sky, best visible at latitudes between +90 and -60 degrees in December. The constellation belongs to the Perseus family of constellations. Its Latin genitive is Persei, the form used when naming stars within the constellation — for example, the brightest star Mirfak may appear in catalogues as Alpha Persei 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 Perseus is Mirfak. Individual stars within Perseus are conventionally named using Bayer designation — Greek letters followed by the Latin genitive of the constellation name (Persei) — introduced by Johann Bayer in his 1603 star atlas Uranometria. Flamsteed numbers (numeric designators followed by Perseus) were added by John Flamsteed in his 1712 catalogue. Variable stars, double stars, and deep-sky objects within the Perseus boundary are catalogued by the IAU with the abbreviation Per.
History and mythology
The figure of Perseus 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 Perseus mean?
Perseus 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 Perseus are designated using the genitive form of the name (e.g. Alpha Perseus 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 Perseus compared to other constellations?
Perseus covers 615 square degrees of sky. The full sphere of the sky contains 41,253 square degrees, so Perseus occupies about 1.5% 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 Perseus visible?
Perseus is primarily a northern hemisphere constellation, best seen from mid-northern latitudes. Southern hemisphere observers may see it low on the horizon depending on their latitude. The brightest star, Mirfak, 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.
