The shock waves from the explosion of Praxis in The Undiscovered Country, the first film to feature such an effect
The Praxis effect (also known as the Praxis explosion or Praxis ring) is a special effect sometimes used in science fiction movies and other visual media. The effect is most commonly seen following the explosion of a large object in space — a ring or disc of matter or energy expanding out from the destroyed object. It was first used in the 1991 science fiction film Star Trek VI: The Undiscovered Country.
The first acknowledged use of the effect was in the 1991 science fiction film Star Trek VI: The Undiscovered Country. The over-mined Klingon moon of Praxis (after which the effect was named) explodes and throws a ring-like shock wave through space, precipitating the events of the film.
The same visual effect is seen in the background of the cover of the 1992 comic book Supreme #1.
Astronomer Philip Plait has described the explosion and resultant shock wave as "the most dramatic effect ever filmed", but states that in reality it would be more likely for such the explosion seen in Star Trek VI: The Undiscovered Country to generate a spherical shock wave. He finds the effect to be more plausible when appearing in the Special Edition of Star Wars Episode IV: A New Hope during the explosion of Alderaan and the Death Star, as an explosion traveling from the core of the space station would reach the equatorial trench before the surface of the station and find no resistance at this point. The Praxis effect was perpendicular to the trench in this shot, instead of on the same plane. However, when the Second Death Star explodes at the end of the Special Edition of Star Wars Episode VI: Return of the Jedi, the Praxis effect is on the same plane as the equatorial trench.