The Perseus Arm is one of two major

spiral arm Spiral arms are a defining feature of spiral galaxies. They manifest as spiral-shaped regions of enhanced brightness within the galactic disc. Typically, spiral galaxies exhibit two or more spiral arms. The collective configuration of these arms i ...

s of the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

galaxy. The second major arm is called the

Scutum–Centaurus Arm The Scutum–Centaurus Arm, also known as Scutum-Crux arm, is a long, diffuse curving streamer of stars, gas and dust that spirals outward from the proximate end of the Milky Way's central bar. The Milky Way has been posited since the 1950s to h ...

. The Perseus Arm begins from the

distal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...

end of the long

central bar. Previously thought to be 13,000 light-years away, it is now thought to lie 6,400 light years from the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Overview

The Milky Way is a

barred spiral galaxy A barred spiral galaxy is a spiral galaxy with a central bar-shaped structure composed of stars. Bars are found in about two thirds of all spiral galaxies in the local universe, and generally affect both the motions of stars and interstellar gas ...

with two major arms and a number of minor arms or spurs. The Perseus Spiral Arm, with a radius of approximately 10.7

kiloparsecs The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

, is located between the minor Cygnus and

Carina–Sagittarius Arm The Carina–Sagittarius Arm (also known as the Sagittarius Arm or Sagittarius–Carina Arm, labeled -I) is generally thought to be a minor spiral arm of the Milky Way galaxy. Each spiral arm is a long, diffuse curving streamer of stars that radia ...

s. It is named after the

Perseus constellation Perseus is a constellation in the northern sky, named after the Greek mythological hero Perseus. It is one of the 48 ancient constellations listed by the 2nd-century astronomer Ptolemy, and among the 88 modern constellations defined by the Inte ...

in the direction of which it is seen from Earth. Recently, scientists in two large radio astronomy projects, the Bar and Spiral Structure Legacy (BeSSeL) Survey and the Japanese VLBI Exploration of Radio Astrometry (VERA), have made great efforts over about 20 years to measure the trigonometric parallaxes toward about 200 water vapor () and

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

() masers in massive star-forming regions in the Milky Way. They have employed these parallax measurements to delineate the forms of spiral arms from the Galactic longitude 2 to 240 degrees and extended the spiral arm traces into the portion of the Milky Way seen from the Southern Hemisphere using tangencies along some arms based on carbon monoxide emission. The image clearly presents the Milky Way as a barred spiral galaxy with fairly symmetric four major arms and some extra arm segments and spurs. The Perseus Arm is one of the four major arms. The arm is the length of more than 60,000 lr and the width of about 1,000 lr and the spiral extension in the pitch angle near 9 degree. There is speculation that the local spur known as the

Orion–Cygnus Arm The Orion Arm, also known as the Orion–Cygnus Arm, is a minor spiral arm within the Milky Way Galaxy spanning in width and extending roughly in length. This galactic structure encompasses the Solar System, including Earth. It is sometimes r ...

, which includes the

and

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

and is located inside of the Perseus Arm, or is a branch of it, but this is unconfirmed. The Perseus Arm contains the

Double Cluster The Double Cluster, also known as Caldwell 14, consists of the open clusters NGC 869 and NGC 884 (often designated h Persei and χ (chi) Persei, respectively), which are close together in the constellation Perseus. Both visible to the ...

and a number of

Messier objects The Messier objects are a set of 110 astronomical objects catalogued by the French astronomer Charles Messier in his ' (''Catalogue of Nebulae and Star Clusters''). Because Messier was interested only in finding comets, he created a list of thos ...

: *The

Crab Nebula The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus (constellation), Taurus. The common name comes from a drawing that somewhat resembled a crab with arm ...

(M1) * Open Cluster M36 * Open Cluster M37 * Open Cluster M38 * Open Cluster M52 * Open Cluster M103.

References

External links

Messier Objects in the Milky Way Galaxy (SEDS)
{{Portal bar, Stars, Outer space Milky Way arms Galactic astronomy Spiral galaxies

Overview

See also

References

External links