Generalities: it is an important  wide constellation of the northern sky. It contains the great spiral galaxy M31. This constellation transits at midnight in September.

Origins and mythology: it is one of the original Ptolemaic constellations. Andromeda represents the beautiful daughter of  king Cepheus and the Ethiopian queen Cassiopeia. According to the mythology the latter offended Neptune, the sea god , saying that her daughter Andromeda was more beautiful than all the sea nymphs. Therefore Neptune sent  a monster to destroy the kingdom and the only way of soothing his anger was  to sacrifice  young Andromeda chaining her to a rock, near which the sea monster would have devoured her. The young girl was sent for the sacrifice but the hero Perseus, returning to the country after having defeated Jellyfish,saved the girl , turning the monster into stone by showing him  the head of Jellyfish (who petrified whoever  looked at her). After this heroic deed, Perseus married Andromeda.
Cepheus, Cassiopea, Perseus and Andromeda are constellations that are in the same sky zone, just because they are  tied to each other by  mythology

Table of stars brighter than magnitude 3.5
 

Star	Proper name	Magnitude	Spectrum	Colour	Distance (light-years)	Notes
Alpha	Alpheratz	2.06	A0p	white	90
Beta	Mirach	2.06	M0	red	75
Gamma	Almach	2.12  (2.18-5.03)	K2-A0	orange+white	120	Visual double star
Delta		3.27	K3	orange	160
51		3.57	K3	orange	186
Omicron		3.6 (variable)	B6-A2	white	114	Variable between 3.5 and 3.7
Lambda		3.82 (variable)	G8	orange	78	Variable between 3.7 and 4.1
Mu		3.87	A5	white	81

Other objects: M31, the great galaxy of Andromeda,  2.2 million light-years far and containing 400 billion stars, stands out from all of them; it is  the nearest spiral galaxy. Nearby  M32 and M110, two small galaxies satellites of M31, are found.

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