Arms

Galactic Features
Structure Core Rim Waves Arms
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Milky_Way_galaxy3TB.jpg


The Milky Way has four main spiral arms: the Norma and Cygnus arm, Carina-Sagittarius, Scutum-Crux, and Perseus. The Sun is located in a minor arm, or spur, named the Orion Spur.

In addition to this, there are several galactic structures that are smaller arms, the near and far 3KPC arms that follow the galactic bar around on either side, and a much more diffuse, outer arm that splits off of the Perseus arm early on and follows it all the way to the edge of the galactic rim.

The Norma Arm is a minor spiral arm of the Milky Way extending from and around its central hub region. 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 about 50,000 light-years. It is named for the Norma constellation, through which the Arm as seen from Earth passes.

The Carina–Sagittarius Arm (also known as Sagittarius Arm) is generally thought to be a minor spiral arm. The Carina–Sagittarius Arm is one of the most pronounced arms in our galaxy as a large number of young stars and giant molecular clouds are concentrated in it. The Carina–Sagittarius Arm lies between two major spiral arms—Scutum–Centaurus Arm inside and the Perseus Arm outside. It is named for its proximity to the Sagittarius and Carina constellations as seen in the night sky from Earth, in the direction of the galactic center. The Sagittarius Arm is divided into two parts. Curving outward from the galaxy’s central bar is the Sagittarius Arm (Sagittarius bar), which further outward becomes the Carina Arm.

The Orion Arm is a minor spiral arm of the Milky Way some 3,500 light-years across and approximately 10,000 light-years in length. Earth lies within the Orion Arm. It is also referred to by its full name, the Orion–Cygnus Arm, as well as Local Arm, Orion Bridge, Local Spur and Orion Spur. The Orion Arm is named for the Orion constellation, which is one of the most prominent constellations of Northern Hemisphere winter (Southern Hemisphere summer). Some of the brightest stars and most famous celestial objects of this constellation (Betelgeuse, Rigel, the stars of Orion’s Belt, the Orion Nebula) are located within the Orion Arm, as shown on the interactive map below. The Orion Arm is located between the Carina–Sagittarius Arm (toward the Galactic Center) and the Perseus Arm (toward the outside Universe), the latter one of the two major arms of the Milky Way. Long thought to be a minor structure, a “spur” between the two longer adjacent arms Perseus and Carina-Sagittarius, earth scientists believe it might be a branch of the Perseus Arm.

Within the Orion Arm, the Solar System, including Earth, is located close to the inner rim in the Local Bubble, about halfway along the Orion Arm’s length, approximately 26,000 light-years from the Galactic Center.

The Perseus Arm is one of two major spiral arms of the Milky Way galaxy. Perseus Arm begins from the distal end of the long Milky Way. It is 6,400 light years from Earth. The Perseus Spiral Arm, with a radius of approximately 35,000 light-years, is located between the minor Cygnus and Carina–Sagittarius Arms. It is named after the Perseus constellation in the direction of which it is seen from Earth. The local spur known as the Orion–Cygnus Arm, which includes the Solar System and Earth and is located inside of Perseus Arm, and is a branch of it

The Scutum–Centaurus Arm, also known as Scutum-Crux arm, and lies between the minor Carina–Sagittarius Arm and the major Perseus Arm. The Scutum–Centaurus Arm arm starts near the core as the Scutum Arm, then gradually turns into the Centaurus Arm.

The Near 3KPC Arm is located in the fourth galactic quadrant at a distance of about 17,000 light-years from the Sun and 11,000 light-years from the galactic center. Along with the Far 3KPC Arm these inner arms establish the Milky Way Galaxy’s simple symmetry. The Far 3KPC arm is located in the first galactic quadrant at a distance of about 10,000 light-years from the galactic center.

Arms

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