Segmentum Obscurus

Segmentum Obscurus is one of the Imperium's five Segmentum Majoris, the northern cube whose fortress is Cypra Mundi and whose most famous wound is the Eye of Terror.

Cadia, Calixis, Gothic, Scarus, Agripinaa, Belis Corona, Nachmund, Medusa, and the Halo Stars all sit in this half of the map. After the 13th Black Crusade much of it woke up in Imperium Nihilus.

Segmentum Obscurus still matters as the Gate and the dark above Terra, not as a synonym for the Eye. Unofficial fan summaries keep a null parent; this is a primary cube, not Sector Solar.