Zone of Avoidance

The Zone of Avoidance is a band of sky near the Milky Way’s plane where stars, dust, and gas obscure distant galaxies, making them difficult to detect.

Milky Way: The barred spiral galaxy containing the Solar System and billions of other stars. Its crowded disk and interstellar material create the obscuring foreground.
Great Attractor: A concentration of mass in the nearby universe that contributes to the motion of galaxies in its direction. Its location behind the Milky Way made its gravitational influence difficult to map.
Harlow Shapley: An American astronomer who measured the Milky Way’s size and studied its globular clusters. Shapley drew attention to the shortage of known external galaxies along the Galactic plane.
HI Parkes All Sky Survey: A blind southern-sky survey of neutral hydrogen using the Parkes radio telescope. Its radio detections exposed gas-rich galaxies behind the Milky Way.
Large-scale structure of the universe: The arrangement of matter into galaxies, clusters, filaments, and voids across the universe. The obscured band once left a major gap in maps of cosmic structure.
Interstellar extinction: The dimming of light as it passes through dust and gas between stars. Dust dims and reddens background galaxies along lines of sight through the Galactic plane.
Norma Cluster: A massive galaxy cluster in the direction of the constellation Norma, near the Milky Way’s plane. Its discovery helped trace mass concentrations inside the Zone of Avoidance.
Bart Bok: A Dutch-American astronomer known for research on the Milky Way and interstellar matter. Bok helped establish the term “Zone of Avoidance” for the apparent galactic gap.
Arecibo Observatory: A former radio observatory in Puerto Rico, known for its 305-meter telescope. Arecibo surveys detected neutral-hydrogen galaxies in parts of the obscured sky.
Peculiar velocity: A galaxy’s motion relative to the uniform expansion of the universe. Incomplete galaxy maps complicated attempts to explain local motions toward hidden mass.

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