Pegasus (constellation)

Pegasus is a constellation in the northern sky, named after the winged horse Pegasus in Greek mythology. It was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and remains one of the 88 modern constellations.
==Notable features==
===Stars===
α Peg (Markab), β Peg, and γ Peg, together with α Andromedae (Alpheratz or Sirrah) form the large asterism known as the Square of Pegasus.
51 Pegasi, a star in this constellation, is the first Sun-like star known to have an extrasolar planet.
IK Pegasi is the nearest supernova candidate.
Spectroscopic analysis of HD 209458 b, an extrasolar planet in this constellation has provided the first evidence of atmospheric water vapor beyond the solar system, while extrasolar planets orbiting the star HR 8799 also in Pegasus are the first to be directly imaged.
=== Named stars ===
Name 	Bayer designation	Origin	Meaning
Markab 	α 	Arabic	the saddle of the horse
Scheat 	β 	Arabic	the leg
Algenib 	γ 	Arabic	the flank
Enif 	ε 	Arabic	nose
Homam 	ζ 	Arabic	man of high spirit
Matar 	η 	Arabic	lucky rain of shooting stars
Baham 	θ 	Arabic	the livestocks
Sadalbari	μ 	Arabic	luck star of the splendid one
===Deep-sky objects===
M15 (NGC 7078) is a globular cluster of magnitude 6.4, 34,000 light-years from Earth. It is a Shapley class IV cluster, which means that it is fairly rich and concentrated towards its center. M15 was discovered in 1746 by Jean-Dominique Maraldi.
NGC 7331 is a spiral galaxy located in Pegasus, 38 million light-years distant with a redshift of 0.0027. It was discovered by musician-astronomer William Herschel in 1784 and was later one of the first nebulous objects to be described as "spiral" by William Parsons. Another of Pegasus's galaxies is NGC 7742, a Type 2 Seyfert galaxy. Located at a distance of 77 million light-years with a redshift of 0.00555, it is an active galaxy with a supermassive black hole at its core. Its characteristic emission lines are produced by gas moving at high speeds around the central black hole.
Pegasus is also noted for its more unusual galaxies and exotic objects. Einstein's Cross is a quasar that has been lensed by a foreground galaxy. The elliptical galaxy is 400 million light-years away with a redshift of 0.0394, but the quasar is 8 billion light-years away. The lensed quasar resembles a cross because the gravitational force of the foreground galaxy on its light creates four images of the quasar. Stephan's Quintet is another unique object located in Pegasus. It is a cluster of five galaxies at a distance of 300 million light-years and a redshift of 0.0215. First discovered by Édouard Stephan, a Frenchman, in 1877, the Quintet is unique for its interacting galaxies. Two of the galaxies in the middle of the group have clearly begun to collide, sparking massive bursts of star formation and drawing off long "tails" of stars. Astronomers have predicted that all five galaxies may eventually merge into one large elliptical galaxy.
===Meteor showers===
The Eta Pegasids radiate from the area near Eta Pegasi every year on May 30.
==History==
The Babylonian constellation IKU (field) had four stars of which three were later part of the Greek constellation Hippos (Pegasus). Pegasus, in Greek mythology, was a winged horse with magical powers. One myth regarding his powers says that his hooves dug out a spring, Hippocrene, which blessed those who drank its water with the ability to write poetry. Pegasus was the one who delivered Medusa's head to Polydectes, after which he travelled to Mount Olympus in order to be the bearer of thunder and lightning for Zeus. Eventually, he became the horse to Bellerophon, who was asked to kill the Chimera and succeeded with the help of Athena and Pegasus. Despite this success, after the death of his children, Bellerophon asked Pegasus to take him to Mount Olympus. Though Pegasus agreed, he plummeted back to Earth after Zeus either threw a thunderbolt at him or made Pegasus buck him off.
In ancient Persia, Pegasus was depicted by al-Sufi as a complete horse facing east, unlike most other uranographers, who had depicted Pegasus as half of a horse, rising out of the ocean. In al-Sufi's depiction, Pegasus's head is made up of the stars of Lacerta the lizard. Its right foreleg is represented by β Peg and its left foreleg is represented by η Peg, μ Peg, and λ Peg; its hind legs are marked by 9 Peg. The back is represented by π Peg and μ Cyg, and the belly is represented by ι Peg and κ Peg.
===In non-Western astronomy===
In Hindu astronomy, the Great Square of Pegasus contained the 26th and 27th lunar mansions. More specifically, it represented a bedstead that was a resting place for the Moon.
Warrau and Arawak peoples in Guyana used the stars in the Great Square to represent a grill on stilts.
==Visualizations==
thumb|300px|right|Diagram of H.A. Rey's alternative way to connect the stars in the constellation Pegasus, showing it as a winged horse.
Pegasus is dominated by an asterism in the shape of a rough square, although one of the stars, Delta Pegasi or Sirrah, is now officially considered to be part of Andromeda, (α Andromedae) and is more usually called "Alpheratz". Traditionally, the body of the horse consists of a quadrilateral formed by the stars α Peg, β Peg, γ Peg, and α And. The front legs of the winged horse are formed by two crooked lines of stars, one leading from η Peg to κ Peg and the other from μ Peg to 1 Pegasi. Another crooked line of stars from α Peg via θ Peg to ε Peg forms the neck and head; ε is the snout.
H.A. Rey has suggested an alternative way to connect the stars into the shape of a winged horse, as seen in the diagram at right. In this visualization, the Square of Pegasus is broken into a triangle, representing the horse's wings, by the removal of Alpha Andromedae.
==Namesakes==
USS Pegasus (AK-48) and USS Pegasus (PHM-1) are United States navy ships named after the constellation "Pegasus".
==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: Pegasus
*Star Tales – Pegasus
 
Category:Constellations
Category:Northern constellations
Category:Constellations listed by Ptolemy