Carina–Sagittarius Arm

The Milky Way is a barred spiral galaxy, consisting of a central crossbar and bulge from which two major and several minor spiral arms radiate outwards. This arm lies between two major spiral arms, the Scutum–Centaurus Arm, the near part of which is visible looking inward, i.e. toward the Galactic Center with the rest beyond the galactic central bulge, and the Perseus Arm, similar in size and shape but locally much closer looking outward, away from the bright, immediately obvious extent of the Milky Way in a perfect observational sky. 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°. Extending from the galaxy's central bar is the Sagittarius Arm (Sagittarius bar). Beyond the dissipated zone it is the Carina Arm.

Geometry

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). The results were that the spiral pitch angle of the arms is 7.3 ± 1.5 degrees, and the half-width of the arms of the Milky Way were found to be 0.2 kpc. The nearest part to the Sun is around 1.4 ± 0.2 kpc away.