Orion Arm
The Orion Arm (also the Orion-Cygnus Arm or Local Arm) is the minor spiral arm of the Milky Way that contains the Sun. It is a broad lane of stars, gas and dust roughly 3,500 light-years across and over 10,000 light-years long, home to famous star-forming nebulae like the Orion Nebula. Because we observe it from inside the Galaxy, its large-scale shape is a reconstruction from surveys of stars and gas, not a photograph.
Science
Classification
- Type
- Minor spiral arm (a spur/branch of the Milky Way)
- Our place
- The Sun lies inside it, ~27,000 ly from the galactic centre
- Also called
- Orion-Cygnus Arm; Local Arm; Orion Spur
Scale
- Width
- ~3,500 light-years · estimated (from within)
- Length
- ~10,000+ light-years · estimated (from within)
- Notable within it
- Orion Nebula, Horsehead, Flame, the Pleiades
How we know
- Note
- We sit INSIDE the Galaxy, so the arm's large-scale shape is a reconstruction from radio maps of hydrogen gas and Gaia's 3-D stellar census — never a photograph from outside. In this view the nebulae, clusters and stars are at their REAL measured positions with real images; the dust lanes and the arm band are MODELLED / illustrative, labelled so.
Discovery & history
- Name
- Named for the constellation Orion, toward which its nearby bright star-forming clouds (the Orion Nebula complex) lie.
That the Sun sits in a spiral arm emerged from 20th-century radio maps of hydrogen gas and, since 2013, ESA's Gaia mission charting the 3-D positions of over a billion stars — which showed the Local Arm is a substantial branch of the Milky Way, not the minor spur once assumed.
Images
No official imagery available — this object has never been visited and no officially-licensed depiction exists.