Near 3 kpc Arm
The Near 3 kpc Arm was discovered in the 1950s by astronomer van Woerden and collaborators through 21-centimeter radio measurements of HI. It was found to be expanding away from the center of the Milky Way at more than 50 km/s. This spiral arm contains about 10 million solar masses of gas, mostly hydrogen atoms and molecules. It's named for its distance from the galactic center. It's about 5.2 kpc from the Sun, and is located in the fourth galactic quadrant.
The last attempt to search for star forming regions in the Near 3 kpc Arm showed little star formation occurring in the numerous molecular clouds of this arm.
Along with the Far 3 kpc Arm discovered in 2008, these inner arms establish our Galaxy's simple symmetry.
