Irrational echo

Irrational echoes were a phenomenon on a Tragan Cluster celestial body near the moon Raspar-6 resulting from a large-scale nuclear blast.

Behind the scenes
Irrational echoes were mentioned in a one-page weather forecast titled "Region 29: The West Fissure", written by Bob Carrau for the 1993 book Monsters and Aliens from George Lucas, a publication that collects concept designs and photographs from various George Lucas projects. Lucasfilm employee Leland Chee, who maintains the Holocron continuity database, has indicated that information contained in the book is non-canonical.