Near 3 kpc Arm

The Near 3 kpc Arm (formerly also called Expanding 3 kpc Arm or simply 3 kpc Arm) was discovered in the 1950s by astronomer van Woerden and collaborators through <a href="/facts/Hydrogen_line/fQaWCT2t">21-centimeter</a> radio measurements of HI (<a href="/facts/Atomic_hydrogen/ncVpPbuE">atomic hydrogen</a>). It was found to be expanding away from the center of the <a href="/facts/Milky_Way/ulF6lccN">Milky Way</a> at more than 50 <a href="/facts/Kilometer_per_second/hSEkho3J">km/s</a>. This <a href="/facts/Spiral_arm/hRT2dtxJ">spiral arm</a> contains about 10 million <a href="/facts/Solar_mass/j6Auhku8">solar masses</a> of gas, mostly hydrogen atoms and molecules. It is named for its distance (more accurately, 3.3 <a href="/facts/Parsec/SwSsk57J">kpc</a>) from the <a href="/facts/Galactic_Center/TI4MwWwM">Galactic Center</a>. It is about 5.2 kpc from the <a href="/facts/Sun/CadPCVHh">Sun</a>, and is located in the fourth <a href="/facts/Galactic_quadrant/YRLmL9Ub">galactic quadrant</a>.
The last attempt to search for star forming regions in the Near 3 kpc Arm (in 1980) showed little <a href="/facts/Star_formation/SMyfVDY6">star formation</a> occurring in the numerous molecular clouds of this arm.
Along with the <a href="/facts/Far_3_kpc_Arm/WtHKm45c">Far 3 kpc Arm</a> discovered in 2008, these inner arms establish the Milky Way galaxy's simple symmetry.

Near 3 kpc Arm open-in-new

Near 3 kpc Arm