Perseus Arm

Short description: One of two major spiral arms of the Milky Way galaxy

Observed structure of the Milky Way's spiral arms.

The Perseus Arm is one of two major spiral arms of the Milky Way galaxy. The second major arm is called the Scutum–Centaurus Arm. The Perseus Arm begins from the distal end of the long Milky Way central bar.[1] Previously thought to be 13,000 light-years away, it is now thought to lie 6,400 light years from the Solar System.[2]

## Contents

* 1 Overview
* 2 See also
* 3 References
* 4 External links

## Overview

The Milky Way is a barred spiral galaxy with two major arms and a number of minor arms or spurs.[1] The Perseus Spiral Arm, with a radius of approximately 10.7 kiloparsecs, is located between the minor Cygnus and Carina–Sagittarius Arms.[1] It is named after the Perseus constellation 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 about 20 years to measure the trigonometric parallaxes toward about 200 water vapor (H2O) and methanol (CH3OH) 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.[3][4]

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.[3]

There is speculation that the local spur known as the Orion–Cygnus Arm, which includes the Solar System and Earth and is located inside of the Perseus Arm,[1] is a branch of it, but this is unconfirmed.

The Perseus Arm contains the Double Cluster and a number of Messier objects:

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

## See also

* Galactic disc
* List of Messier objects

## References

1. ↑ 1.0 1.1 1.2 1.3 Churchwell, Ed; Babler, Brian L.; Meade, Marlin A. (2009). "The Spitzer/GLIMPSE Surveys: A New View of the Milky Way" (pdf). Publications of the Astronomical Society of the Pacific 121: 213–230. doi:10.1086/597811. Bibcode: 2009PASP..121..213C. http://www.astro.wisc.edu/sirtf/Churchwell_2009.pdf.
2. ↑ McKee, Maggie (8 December 2005). "Spiral arm of Milky Way looms closer than thought". New Scientist. Reed Business Information Ltd. https://www.newscientist.com/article/dn8436#.UnJSsvmnq1U.
3. ↑ 3.0 3.1 Reid, M. J. et al. (2009). "Trigonometric parallaxes of massive star-forming regions. VI. Galactic structure, fundamental parameters, and noncircular motions". The Astrophysical Journal 700 (1): 137–148. doi:10.1088/0004-637X/700/1/137. Bibcode: 2009ApJ...700..137R.
4. ↑ Hirota, T., Hirota, T., Nagayama, T., Honma, M., et al. 2020, PASJ,72,50

## External links

* Messier Objects in the Milky Way Galaxy (SEDS)

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The Milky Way

Location|

Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Observable universe → Universe
Each arrow (→) may be read as "within" or "part of".

Galactic core|

* Center of the Milky Way
* Sagittarius A
* Sagittarius A*
* Supermassive black hole

Spiral arms|

* Carina–Sagittarius
* Norma–Cygnus
* Orion–Cygnus
* Perseus
* Scutum–Centaurus

Satellite galaxies|

| Magellanic Clouds|

* Large Magellanic Cloud
* Small Magellanic Cloud
* Magellanic Stream
* Magellanic Bridge

|

Sagittarius Spheroidal|

* Sagittarius Stream
* Boötes II
* Coma Berenices
* Messier 54
* Palomar 12
* Segue 1
* Segue 2
* Terzan 7

Dwarfs|

* Antlia 2
* Boötes I
* Boötes III
* Canes Venatici I
* Canes Venatici II
* Canis Major
* Carina
* Crater 2
* Draco
* Fornax
* Hercules
* Leo I
* Leo II
* Leo IV
* Leo V
* Leo T
* Phoenix
* Pisces I
* Pisces II
* Sculptor
* Sextans
* Triangulum II
* Ursa Major I
* Ursa Major II
* Ursa Minor
* Virgo I

Other|

* Gaia Sausage
* Monoceros Ring
* Virgo Stream
* Koposov I
* Koposov II
* Segue 3
* Willman 1

Related|

* Andromeda–Milky Way collision
* Baade's Window

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