And · Andromedae
Andromeda Constellation
IAU constellation mapAndAndromeda (And) is one of the 88 constellations recognised by the International Astronomical Union. It covers 722 square degrees of the northern sky in quadrant NQ1. Its brightest star is Alpheratz. The Latin genitive of the name is Andromedae, used to form star names within the constellation. In Greek mythology, Andromeda is associated with greek tradition. The IAU standardised all constellation boundaries in 1930.
Quick facts
- IAU name
- Andromeda
- Abbreviation
- And
- Latin genitive
- Andromedae
- Hemisphere
- northern
- Area
- 722 sq deg
- Brightest star
- Alpheratz
- Quadrant
- NQ1
- Family
- Perseus
- Mythology origin
- Greek
- Discovery era
- Ptolemy's 48 (Almagest, c. 150 CE)
Mythology
Andromeda, the chained princess, is one of the characters in the famous Perseus cycle of myths. Her mother, Queen Cassiopeia of Ethiopia, boasted that Andromeda was more beautiful than the Nereids, the sea-nymphs. Poseidon, enraged at this slight to his divine handmaidens, sent the sea monster Cetus to devastate the coastline. An oracle told King Cepheus that the only remedy was to sacrifice his daughter Andromeda to the monster. She was accordingly chained to a coastal rock as an offering — but the hero Perseus, returning through the sky with the severed head of Medusa, saw her plight and fell in love with her. He killed Cetus (some accounts say by showing it the Gorgon's head, turning it to stone; others that he slew it with his sword), freed Andromeda, and married her. The Andromeda Galaxy (Messier 31) — the most distant object visible to the naked eye at about 2.537 million light-years — lies within this constellation, a spiral galaxy similar to and larger than the Milky Way, with which it will eventually merge in about 4.5 billion years.
Sources: Apollodorus Bibliotheca 2.4.3; Hyginus Astronomica 2.11; Ovid Metamorphoses 4.663-764.
Overview
Andromeda is one of the 88 constellations formally recognised by the International Astronomical Union (IAU). It occupies 722 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 Andromedae, the form used when naming stars within the constellation — for example, the brightest star Alpheratz may appear in catalogues as Alpha Andromedae 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 Andromeda is Alpheratz. Individual stars within Andromeda are conventionally named using Bayer designation — Greek letters followed by the Latin genitive of the constellation name (Andromedae) — introduced by Johann Bayer in his 1603 star atlas Uranometria. Flamsteed numbers (numeric designators followed by Andromeda) were added by John Flamsteed in his 1712 catalogue. Variable stars, double stars, and deep-sky objects within the Andromeda boundary are catalogued by the IAU with the abbreviation And.
History and mythology
The figure of Andromeda 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 Andromeda mean?
Andromeda 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 Andromeda are designated using the genitive form of the name (e.g. Alpha Andromeda 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 Andromeda compared to other constellations?
Andromeda covers 722 square degrees of sky. The full sphere of the sky contains 41,253 square degrees, so Andromeda occupies about 1.8% 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 Andromeda visible?
Andromeda 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, Alpheratz, 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.
