Why was the Norma Arm of the Milky Way galaxy given that name?

Answer 1

It's also called the Cygnus Arm or Cygnus-Norma Arm, which might give you a clue to the source of the name if you're more familiar with northern constellations than southern ones. Norma is one of the constellations the Milky Way passes through. It's otherwise fairly unremarkable, consisting mainly of two moderately bright stars, so it's not surprising that many people have never heard of it.

Answer 2

The Norma Arm was named after the Norma star-forming region, which is located in that region of the Milky Way galaxy. It is one of the spiral arms extending from the galactic center. The naming convention for galactic arms is often based on nearby prominent celestial objects or regions.