Perseus is a constellation in the northern hemisphere. It was first charted by the Greek astronomer Ptolemy in the 2nd century. The constellation was named after the mythical hero Perseus. In Greek mythology, Perseus was the son of Zeus and Danaë, daughter of Acrisius, the king of Argos. Acrisius had kept his daughter locked away in a dungeon because an oracle had told him that he would die by his grandson’s hand. Zeus, determined to conquer Danaë, transformed himself into golden rain, falling into her lap, and got her pregnant.
The most famous stories about Perseus involve the Gorgon Medusa and the princess Andromeda. It was King Polydectes, Danaë’s unwanted suitor, who sent Perseus to get the head of the Gorgon as a wedding gift to himself and a woman he said he intended to marry to get Perseus out of the way. Medusa was the only mortal of the three hideous Gorgon sisters, whose gaze could turn people into stone. She had tusks, snakes for hair, golden wings and brass hands. Perseus waited until she was asleep and then decapitated her. On his way home, he came across the princess Andromeda, who was chained to a rock and left to the sea monster Cetus. He rescued her and took her home to Seriphos with him. Polydectes, who had hoped that Perseus would not come back, was hostile when Perseus returned. Perseus, angered by the king, took out Medusa’s head and turned him into a stone. The constellation Perseus is located next to Andromeda
, the constellation that represents his wife.
The constellation Perseus occupies an area of 615 square degrees and contains three stars with known planets. It can be seen at latitudes between +90° and -35° and is best visible at 9 p.m. during the month of December.
The brightest star in Perseus is 
alpha Persei, also known by its traditional names Mirfak ("elbow") and Algenib ("the side"). Mirfak is a yellow-white supergiant lying approximately 590 light-years from Earth. Its luminosity is 5,000 that of the Sun. Mirfak is the title member of the Alpha Persei Cluster, an open star cluster also known as Collinder 39 or Melotte 20. Other bright stars in the cluster are 
epsilon and 
beta Persei is much better known by its traditional name, Algol, from the Arabic phrase "ra’s al-ghul," meaning "head of the ogre." In the 16th century, the star was known by its Latin name, Caput Larvae, which means "spectre’s head." The British sometimes call it Demon Star or The Ghoul. The star’s Hebrew name is "Rosh ha Satan," or "Satan’s head." The Chinese know it as Tseih She ("piled up corpses") or "the Fifth Star of the Mausoleum." Algol marks the head of the Gorgon Medusa, which Perseus is holding. Medieval astrologers considered it the most unfortunate star in the sky.
Algol is an eclipsing spectroscopic binary star, in fact a triple star system, and one of the first variables found in the sky. It is 92.8 light-years distant from Earth. The primary component is a B8 main sequence star and the companion is a K2-type subgiant.
zeta Persei is another supergiant, B class, approximately 980 light-years away. It has the luminosity 105,000 times that of the Sun. The primary star has four companions: two dwarfs and two line-of-sight coincidences.
epsilon Persei, or Adid Australis ("southern one of the upper arm"), is another multiple star system with a blue, class B main sequence star and a white companion as the primary components. Adid Australis is approximately 540 light-years distant from Earth.
gamma Persei, also known as Al Fakhir or Alpecher ("the excellent one") and Seid ("forearm"), is another multiple star system. It consists of a yellow giant and a white companion star. The system lies approximately 260 light-years away.
delta Persei, or Adid Borealis ("the northern one of the upper arm") is a blue giant about 530 light-years away. The star has another traditional name, Basel, which means "the brave one."
iota Persei is a Sun-like star lying relatively close to our solar system, only 34 light-years away. It is a main sequence dwarf, slightly larger and more massive than the Sun.
GK Persei, or Nova Persei 1901, was one of the brightest novae in modern times. It occurred in 1901, about 1,500 light-years away. Rather than fading away, the star occasionally displays outbursts of 2 to 3 magnitudes, which occur once every three years and last for about two months.
Perseus also contains several notable deep sky objects. The Double Cluster, consisting of the open clusters NGC 884 and NGC 869, can be seen by the naked eye. Both clusters are relatively young; one is estimated to be 5.6 million years of age, while the other is 3.2 million years old. The Double Cluster is on the list of the Royal Astronomical Society of Canada's Finest N.G.C. Objects.
Messier 34 (NGC 1039) is another open star cluster, with about 400 member stars, approximately 1,500 light-years distant. The age of the cluster is estimated at 180 million years.
The Little Dumbbell Nebula (NGC 650/651, Messier 76) is sometimes also called the Barbell Nebula or the Cork Nebula. It got its name after the Dumbbell Nebula (Messier 27) in the constellation Vulpecula
, which it resembles. It has two numbers in the New General Catalogue (NGC) because it was believed to consist of two separate nebulae. It is a rather faint object, with an apparent magnitude of 10.1.
The California Nebula (NGC 1499) is an emission nebula that got its name because it resembles the outline of the State of California. It was discovered in the mid-19th century by the American astronomer Edward E. Barnard. Approximately 1,000 light-years distant, the California Nebula is hard to observe without an H-beta filter because it has a very low surface brightness.
NGC 1333 is a reflection nebula lying about 1,000 light-years from Earth. The clouds of dust and gas are illuminated by the light of a dense group of newborn stars, split into two sub-clusters: one appearing red and the other yellow and green.
NGC 1260 is a spiral galaxy that was the site of the second brightest, most violent star death ever observed, the supernova SN 2006gy. The explosion, which could be referred to as a hypernova or quark-nova, was 100 times more energetic than a typical supernova. Its brightness reached its peak only after 70 days, when it emitted more than 50 billion Suns' worth of light. The galaxy in which the explosion occurred is approximately 238 light-years distant.
Perseus belongs to the Perseus family of constellations, along with Cassiopeia
Constellations directly bordering Perseus are Cassiopeia