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The Milky Way Galaxy is structured as barred spiral, and emerging from the end of its central bar currently closest to the Solar System are a pair of galactic arms. One of these, the Scutum-Crux Arm, is a long, dense structure that passes between the galaxy's core and the Sun's current position, and continues to spiral on around the entire Galaxy.

Also emerging from the near end of the bar is a second arm, far less dense than the major Scutum-Crux Arm. This arm forms a trailing filament that passes between the Scutum-Crux Arm and the Sun's current position before trailing off into intergalactic space. While this minor arm is sometimes called the 'Sagittarius Arm' in its entirety, the full structure is more properly called the 'Carina-Sagittarius Arm'. The term 'Sagittarius Arm' properly refers to the parts that lie in the inner Galaxy, where it passes through the constellation of Sagittarius as seen from Earth.


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