[1] Each spiral arm is a long, diffuse curving streamer of stars that radiates from the Galactic Center.
[1] 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 arm dissipates near its middle, shortly after reaching its maximal angle, viewed from the Solar System, from the Galactic Center of about 80°.
[1] A study was done with the measured parallaxes and motions of 10 regions in the Sagittarius arm where massive stars are formed.
Data was gathered using the BeSSeL Survey with the VLBA, and the results were synthesized to discover the physical properties of these sections (called the Galactocentric azimuth, around −2 and 65 degrees).