The Norma Arm is a minor spiral arm of the Milky Way galaxy extending from and around the central hub region of the Milky Way Galaxy. The inner portion of the Arm is called Norma Arm in narrow meaning. The outer part of it is identified either with Cygnus Arm, which lies outside the Perseus Arm, or Outer Arm, which is located further away from the center of the Galaxy than Cygnus Arm. Norma Arm has a radius of 15.5 ± 2.8 kpc. It is named for the Norma constellation, through which the Arm as seen from Earth passes.
The Milky WayGalaxy in which the Sun dwells, in common with many other galaxies of similar type, consists of a large mass of stars drawn by gravitational forces into the form of a relatively flat disc. The disc is rotating, with the dense central body of stars moving at greater speeds than those towards the rim of the disc. As a result, the pattern of stars within the Galaxy as viewed from directly above or below the disc has formed into a spiral.
Because of localised gravitational variations, the spiral pattern has itself formed several distinct 'spiral arms', where particularly large numbers of stars can be found.