The Norma Arm is a minor spiral arm of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

extending from and around its central hub region. The inner portion of the Arm is called the ''Norma Arm'' in narrow meaning. The outer part of it is identified either with the Cygnus Arm, which lies outside the

Perseus Arm The Perseus Arm is one of two major spiral arms of the Milky Way galaxy. The second major arm is called the Scutum–Centaurus Arm. The Perseus Arm begins from the distal end of the long Milky Way central bar. Previously thought to be 13,000 lig ...

, or the Outer Arm, which is located farther away from the center of the Galaxy than the Cygnus Arm. The Norma Arm begins from the

Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact rad ...

, and extends outward to a radius of . It is named for the

Norma Norma may refer to: * Norma (given name), a given name (including a list of people with the name) Astronomy *Norma (constellation) * 555 Norma, a minor asteroid *Cygnus Arm or Norma Arm, a spiral arm in the Milky Way galaxy Geography *Norma, Lazi ...

constellation, through which the Arm as seen from Earth passes. Like many other galaxies of similar type, the Milky Way consists of a large mass of

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s shaped into the form of a relatively flat disc by

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

. The disc is rotating, with the dense central body of stars moving at greater speeds than those toward 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.

References

{{Portal bar, Stars, Spaceflight, Outer space, Solar System Milky Way arms Galactic astronomy Spiral galaxies

See also

References