Perseus Arm

The Perseus Arm is a major spiral arm of the Milky Way, extending through the Galaxy’s outer regions beyond the Sun’s position. It contains clouds of gas and dust, star-forming regions, and young stars.

Milky Way: The barred spiral galaxy that contains the Solar System and billions of other stars. The Perseus Arm is one of the Milky Way’s large-scale spiral features.
Spiral arm: An elongated region of enhanced stars, gas, and dust in the disk of a spiral galaxy. The Perseus Arm is a specific large-scale example of this galactic structure.
W3 star-forming region: A massive star-forming complex in the constellation Cassiopeia, associated with the Perseus Arm. Its masers have supplied precise distance and motion measurements for the arm.
Orion Arm: A minor spiral arm or spur of the Milky Way that contains the Sun and Solar System. The Sun lies in the Orion Arm, inside the Perseus Arm’s general outer direction.
Spiral galaxy: A galaxy with a flattened disk and spiral patterns of stars, gas, and dust. The arm’s shape and stellar populations are features of spiral-galaxy structure.
Density wave theory: A model in which spiral patterns move through a galactic disk as waves of increased matter density. It offers one explanation for how spiral patterns can persist while stars orbit at different speeds.
W4 (Heart Nebula): An emission nebula in Cassiopeia containing a young stellar cluster and surrounding ionized gas. It is a prominent star-forming complex in the direction of the Perseus Arm.
Sagittarius Arm: A major spiral arm of the Milky Way located inward from the Sun’s orbit. Its inner-Galaxy position contrasts with the Perseus Arm’s outer-disk location.
Galactic coordinate system: A celestial coordinate system that locates objects by longitude and latitude relative to the Milky Way’s plane and center. Astronomers use it to describe the arm’s position across the Galactic disk.
H II region: A cloud of ionized hydrogen surrounding young, hot stars that emit ultraviolet radiation. These luminous regions mark sites of recent massive-star formation along the arm.

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