Outer arm

Cygnus Arm

The Milky Way Galaxy 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.

The Cygnus Arm (also known as the Outer Arm; the Norma Arm; the Cygnus-Norma arm) is one of four major spiral arms extending from and around the central hub region of the Milky Way Galaxy. The Cygnus arm has a radius of 15.5 ± 2.8 kiloparsecs and lies outside the Perseus Arm. It is named for the Cygnus constellation, through which the Arm as seen from Earth passes.

The 'Norma Arm' is that part of the Cygnus Arm closest to the galactic hub.

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