Perseus (constellation)

Perseus is a constellation in the northern sky, named after the Greek hero Perseus. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations defined by the International Astronomical Union. It contains the famous variable star Algol (β Per), and is also the location of the radiant of the annual Perseids meteor shower.
==Notable features==
*α Per (Mirfak): The brightest star of this constellation is also called Algenib (a name which is used for other stars as well, e. g. γ Peg). Mirfak (Arabic for elbow) is a supergiant of spectral type F5 Ib with an apparent brightness of 1.79m lying at a distance of ca. 590 light-years. Its luminosity is 5,000 times and its diameter is 42 times that of our sun.
*Algol (β Per): The most well-known star in Perseus, Algol (from the Arabic Ra's al-Ghul, which means The Demon's Head) represents the eye of the gorgon Medusa. It was also called Rosh ha Satan ("Satan's Head") by the Hebrew people, who saw Algol as representing Lilith. It is 92.8 light-years from Earth and varies in magnitude from a minimum of 3.5 to a maximum of 2.3. This star is the prototype of a whole group of eclipsing variable stars. Its period is merely 2.867 days. It is a triple star with the brightest component having a spectral type B8 V. 
*Nova Persei 1901 (GK Per), a bright nova discovered on February 21, 1901.
===Deep-sky objects===
*h + χ Per: These two open clusters (NGC 869 and NGC 884 respectively) belong to two objects of the night sky for binoculars and small telescopes. They are sometimes called the Double Cluster. Both lie at distances of more than 7,000 ly and are separated by several hundred light-years. The cluster was first recorded during the reign of the Chinese king Tsung-K'ang, who reigned during the Hsia Dynasty (2858-2146 BCE). Both clusters are of approximately 4th magnitude and 0.5 degrees in diameter. Both are Trumpler class I 3 r clusters, though NGC 869 is a Shapley class f and NGC 884 is a Shapley class e cluster. These classifications indicate that they are both quite rich; NGC 869 is the richer of the pair. Both clusters are distinct from their star field and are clearly concentrated at their centers. The constituent stars, numbering over 100 in each cluster, range widely in brightness.
*M34: This open cluster with an apparent brightness of 5.5m lies at a distance of approximately 1,400 ly and consists of about 100 stars that are scattered over an area larger than that of the full moon. Its true diameter is about 14 ly. M 34 can be resolved even with good binoculars but is best viewed using a telescope at low magnifications.
*M76: This planetary nebula is also called Little Dumbbell Nebula. It measures about 65 arc seconds and has an apparent brightness of 10.1m.
*NGC 1499: Also called California Nebula this emission nebula, discovered in 1884-85 by the American astronomer Edward E. Barnard, is a great target for astrophotographers. Due to its low surface brightness it's a very difficult object when observed visually.
*NGC 1333 is a reflection nebula and the location of star formation.
*NGC 1260 contains the second brightest known object in the universe, SN 2006gy.
*Alpha Persei Cluster (also known as Melotte 20 and Collinder 39) is an open cluster containing Alpha Persei.
*Perseus also contains a giant molecular cloud, named Perseus molecular cloud; it belongs to the Orion Spur and is well known for its low-star formation.
*The Perseus Cluster (Abell 426) is a massive galaxy cluster located 250 million light-years from Earth; at a redshift of 0.0183, it is the closest major cluster to Earth. NGC 1275, a component of the cluster, has an active nucleus that produces massive bubbles surrounding the galaxy with its jets of material. The Perseus Cluster also has sound waves traveling through it, caused by these bubbles, with a note of B flat 57 octaves below middle C.
*NGC 1275 is a member of the Perseus Cluster. It is a cD galaxy that has undergone many mergers throughout its existence, as evidenced by the "high velocity system" surrounding it (the remnants of a smaller galaxy). Its active nucleus is a strong source of radio waves.
===Meteor showers===
The Perseids, an annual meteor shower, radiate from Perseus in late summer.
The September Epsilon Perseids are a recently discovered meteor shower with a parent body in the Oort cloud.
==History==
The Greek constellation may be an adaptation of the Babylonian constellation known as the Old Man (MUL.SHU.GI) which is associated with East (as a cardinal direction) in the MUL.APIN, an astronomical compilation dating to around 1000 BCE.
In Greek mythology, Perseus was the son of Danae, who became the hero who slew Medusa. He later used the Gorgon's head to rescue the princess Andromeda from the monster Cetus.
===In non-Western astronomy===
Four Chinese constellations existed in the area of the sky now assigned to Perseus. T'ien-tchouen, translated as the "Celestial Boat", was the third paranatellon of the third house of the White Tiger of the West. It represented the boats that Chinese people were reminded to build in case of a catastrophic flood season. Tsi-choui, translated as the "Swollen Waters", was the fourth paranatellon of the third house of the White Tiger of the West. It represented the potential of unusually high floods during the beginning of the flood season, which commenced at the end of August and beginning of September. Ta-ling, translated as the "Great Trench", was the fifth paranatellon of the third house of the White Tiger of the West. It represented the trenches where criminals executed en masse in August were interred. The pile of corpses prior to their interment was represented by Tsi-chi (Algol), the sixth paranatellon of the third house of the White Tiger.
The Double Cluster, h and χ Persei, had special significance in Chinese astronomy. Known as Hsi and Ho, the two clusters represented two astronomers who failed to predict a total solar eclipse and were beheaded thereafter.
==Visualizations==
Traditionally, the stars of Perseus are visualized as forming a 'Y' shape.
thumb|right|300px|Diagram of H.A. Rey's alternative way to connect the stars of the constellation Perseus.
H.A. Rey has suggested an alternative way to connect the stars into the shape of a man. Perseus' body is formed by the stars β Per, κ Per, ι Per, α Per, σ Per, ν Per, and ε Per. α Per and β Per are of the second magnitude. The star ε Per is of the third magnitude. The stars α Per, γ Per, τ Per, and ι Per form Perseus' head: gamma Persei is of the third magnitude. Stars γ Per, η Per, and τ Per form Perseus' cap. The stars α Per, ψ Per, δ Per, 48 Per, μ Per, and λ Per form Perseus' left arm and hand: δ Per being of the third magnitude. The stars ι Per, θ Per, and φ Per form the right arm and hand. Perseus' right hand, φ Per, is yanking at one of Andromeda's feet (51 Andromedae), intent on liberating her. Stars ε Per, ξ Per, ζ Per, and ο Per form Perseus' left leg and foot: ζ Per being of the third magnitude. Finally, stars β Per, ρ Per, 16 Per (with π Per) form Perseus' right leg and foot.
==See also==
* V718 Persei
==References==
* 
* H. A. Rey, The Stars — A New Way To See Them. Enlarged World-Wide Edition. Houghton Mifflin, Boston, 1997. ISBN 0-395-24830-2.
* Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0-00-725120-9. Princeton University Press, Princeton. ISBN 978-0-691-13556-4.
==External links==
*The Deep Photographic Guide to the Constellations: Perseus
*SEDS' comprehensive Messier Catalog
*The clickable Perseus
*Star Tales – Perseus
 
Category:Constellations
Category:Northern constellations
Category:Constellations listed by Ptolemy