Andromeda Constellation

Andromeda represents the princess of Greek myth chained to a rock as a sacrifice to a sea monster, only to be rescued at the last moment by the hero Perseus. Its stars form a simple, elegant line extending from the corner of the Great Square of Pegasus, and while the constellation itself is fairly modest to the naked eye, it holds one of the true showpieces of amateur astronomy: the Andromeda Galaxy, the most distant object most people will ever see without a telescope, and the closest large galactic neighbor to our own Milky Way.

Andromeda at a Glance

• AbbreviationAnd
• Genitive FormAndromedae
• MeaningThe Chained Princess
• Constellation FamilyPerseus family
• Area722 sq. degrees (19th largest of 88)
• Right Ascension23h 26m – 2h 40m
• Declination+53.2° to +21.7°
• Brightest StarAlpheratz (magnitude 2.06)
• Best Evening ViewingNovember, visible 90°N to 40°S

Mythology and History

Andromeda was the daughter of King Cepheus and Queen Cassiopeia of Aethiopia. When Cassiopeia boasted that her daughter's beauty surpassed that of the sea nymphs, the offended sea god Poseidon sent the monster Cetus to ravage the kingdom's coast. An oracle warned that only Andromeda's sacrifice would satisfy the god's anger, so she was chained to a rock by the sea to await the monster. The hero Perseus, returning from slaying the Gorgon Medusa, happened upon the scene, turned Cetus to stone with Medusa's severed head, and freed Andromeda, whom he then married. Nearly every character from this myth — Andromeda, Perseus, Cassiopeia, Cepheus, and Cetus — has its own constellation, all clustered together in the same region of autumn sky. Andromeda was one of the 48 constellations recorded by Ptolemy in the 2nd century AD.

Notable Stars in Andromeda

Alpheratz, the brightest star in Andromeda at magnitude 2.06, sits right at the constellation's border and was historically shared with neighboring Pegasus, forming one corner of the Great Square, before formal constellation boundaries assigned it exclusively to Andromeda in the 20th century. Mirach, a cool red giant, is often used by stargazers as a signpost, since a line drawn through it and a fainter neighboring star points almost directly at the Andromeda Galaxy. Almach, meanwhile, is prized by telescope owners for its striking color contrast — a golden-yellow giant paired with a fainter blue-green companion star.

Deep-Sky Objects

Andromeda's centerpiece is the Andromeda Galaxy (M31), a giant spiral galaxy roughly 2.5 million light-years from Earth — the most distant object visible to the naked eye, appearing as a faint, elongated smudge under dark skies. It is the largest member of our Local Group of galaxies and is slowly approaching the Milky Way, with the two expected to merge several billion years from now. Two smaller companion galaxies, M32 and M110, orbit it and are visible in the same telescopic field of view.

• Andromeda Galaxy (M31) — the nearest large spiral galaxy to the Milky Way, roughly 2.5 million light-years away and visible to the naked eye under dark skies as a faint, elongated smudge
• M32 & M110 — two dwarf companion galaxies gravitationally bound to the Andromeda Galaxy, both visible in the same telescopic field of view

Neighboring Constellations and How to Find It

Andromeda is easiest to find by first locating the Great Square of Pegasus, then following the chain of stars extending from its northeastern corner. It climbs highest in the evening sky around November, and the Andromeda Galaxy itself is best viewed from a dark location, well away from city lights. Andromeda borders Perseus, Cassiopeia, Lacerta, Pegasus, Pisces, and Triangulum.

Andromeda is also associated with the Andromedids (Bielids) meteor shower, visible to observers who track where these annual displays radiate from.