Orion Arm

The Orion Arm is a minor spiral arm of the Milky Way Galaxy that is 3,500 light-years (1,100 parsecs) across and approximately 10,000 light-years (3,100 parsecs) in length,[2] containing the Solar System, including Earth. It is also referred to by its full name, the Orion–Cygnus Arm, as well as Local Arm, Orion Bridge, and formerly, the Local Spur and Orion Spur.

Milky Way centre from Sinai, Egypt
For the stars which form the arm of the Orion asterism, see Orion (constellation). For the online project, see Orion's Arm.
Observed structure of the Milky Way's spiral arms[1]

The arm is named for the Orion Constellation, which is one of the most prominent constellations of Northern Hemisphere winter (Southern Hemisphere summer). Some of the brightest stars and most famous celestial objects of the constellation (e.g. Betelgeuse, Rigel, the three stars of Orion's Belt, the Orion Nebula) are within it as shown on the interactive map below.

The arm is between the Carina–Sagittarius Arm (the local portions of which are toward the Galactic Center) and the Perseus Arm (the local portion of which is the main outer-most arm and one of two major arms of the galaxy).

Long thought to be a minor structure, namely a "spur" between the two arms mentioned, evidence was presented in mid 2013 that the Orion Arm might be a branch of the Perseus Arm, or possibly an independent arm segment.[3]

Within the arm, the Solar System is close to its inner rim, in a relative cavity in the arm's Interstellar Medium known as the Local Bubble, about halfway along the arm's length, approximately 8,000 parsecs (26,000 light-years) from the Galactic Center.

Messier objects
The shape of the Orion Spur[4]

The Orion Arm contains a number of Messier objects:

Interactive maps
Rosette NebulaCrab NebulaOrion NebulaTrifid NebulaLagoon NebulaOmega NebulaEagle NebulaNorth America NebulaRigelOrion's BeltPolarisSunBetelgeuseDenebPerseus ArmOrion Arm
Orion and neighboring arms (clickable map)
Rosette NebulaCone NebulaCalifornia NebulaHeart NebulaOrion NebulaNorth America NebulaVeil NebulaTrifid NebulaCrescent NebulaLagoon NebulaOmega NebulaEagle NebulaCrab NebulaMessier 37Messier 36Messier 38Messier 50Messier 46Messier 67Messier 34Messier 48Messier 41Messier 47Messier 45Messier 39Messier 52Messier 93Messier 7Messier 25Messier 23Messier 21Messier 18Messier 26Messier 35NGC 2362IC 2395NGC 3114NGC 3532IC 2602NGC 6087NGC 6025NGC 3766IC 4665IC 2944NGC 3293NGC 6067NGC 6193NGC 6231Messier 103Messier 29Perseus ArmOrion ArmStar clusterNebula
The nearest nebulae and star clusters (clickable map)
Location of Earth
(view • discuss)
Planet Earth
Solar System
Gould Belt
Orion Arm
Milky Way
Local Group
Virgo SCl
Laniakea SCl
Observable
Universe

See also

References
  1. See the "Spiral Arms" part of this NASA animation for details
  2. Harold Spencer Jones, T. H. Huxley, Proceedings of the Royal Institution of Great Britain, Royal Institution of Great Britain, v. 38–39
  3. Earth's Milky Way Neighborhood Gets More Respect, National Radio Astronomy Observatory, Dave Finley, 3 June 2013
  4. Vázquez, Ruben A.; May, Jorge; Carraro, Giovanni; Bronfman, Leonardo; Moitinho, André; Baume, Gustavo (January 2008). "Spiral Structure in the Outer Galactic Disk. I. The Third Galactic Quadrant". The Astrophysical Journal. 672 (2): 930–939. arXiv:0709.3973. Bibcode:2008ApJ...672..930V. doi:10.1086/524003.
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