Praxis effect

The Praxis effect (also known as the Praxis explosion or Praxis ring) is a special effect commonly 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' of matter expanding out from the destroyed object. The first acknowledged use of the effect was in 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.
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 an explosion 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 the Death Star, as an explosion travelling 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. Unfortunately the Praxis effect was perpendicular to the trench in this shot, instead of on the same latitude.
The shock waves in both films were created by Industrial Light and Magic through computer animation.