Pegasus

Pegasus

Constellation
List of stars in Pegasus
Abbreviation	Peg
Genitive	Pegasi
Pronunciation	/ˈpɛɡəsəs/, genitive /ˈpɛɡəsaɪ/
Symbolism	the Winged Horse / Pegasus
Right ascension	23 h
Declination	+20°
Quadrant	NQ4
Area	1121 sq. deg. (7th)
Main stars	9, 17
Bayer/Flamsteed stars	88
Stars with planets	10
Stars brighter than 3.00m	5
Stars within 10.00 pc (32.62 ly)	3
Brightest star	ε Peg (Enif) (2.38m)
Nearest star	EQ Peg (20.38 ly, 6.25 pc)
Messier objects	1
Meteor showers	July Pegasids
Bordering constellations	Andromeda Lacerta Cygnus Vulpecula Delphinus Equuleus Aquarius Pisces
Visible at latitudes between +90° and −60°. Best visible at 21:00 (9 p.m.) during the month of October.

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

Deep-sky objects

• M15 – a globular cluster near the nose (ε Peg) of Pegasus.

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.^[1]

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.^[1] 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.^[1]

History

The Babylonian constellation IKU (field) had four stars of which three were later part of the Greek constellation Hippos (Pegasus).^[2]

Visualizations

Pegasus with the foal Equuleus next to it, as depicted in Urania's Mirror, a set of constellation cards published in London c.1825. The horses appear upside-down in relation to the constellations around them.

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.

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

Wikimedia Commons has media related to: Pegasus (constellation) (category)

• The Deep Photographic Guide to the Constellations: Pegasus
• Star Tales – Pegasus

Coordinates: 23^h 00^m 00^s, +20° 00′ 00″