A by-product was his discovery of the 'zone of avoidance' and his extensive investigation of obscuration by interstellar matter in the Galaxy.

The universal book of astronomy: from the Andromeda Galaxy to the zone of avoidance; Wiley 2004, David J. Darling, pag.

This results in the so-called zone of avoidance, where our view of the extra-galactic sky is severely hampered, and background galaxies, such as Dwingeloo 1, were only discovered recently through observations in radio and infrared.

Additionally, the ejecta from oblique impacts show distinctive patterns at different impact angles: asymmetry starting around 60˚ and a wedge-shaped "zone of avoidance" free of ejecta in the direction the projectile came from starting around 45˚.

The gas and dust from the Milky Way (known as the Zone of Avoidance) obscure the view of astronomers and have so far made it impossible to determine if the wall ends or continues on further than they can currently observe.