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 is named after the explosion of the fictional Klingon moon Praxis at the start of the 1991 science fiction film Star Trek VI: The Undiscovered Country.
The first known use of the effect was in the 1979 science fiction film Alien during the self-destruction of the spaceship Nostromo. It first forms a horizontal multicolored line, with an orange sphere behind or inside it. The shockwave strikes Ellen Ripley's ship a moment later. A similar effect occurs during the evolution of V'Ger in Star Trek: The Motion Picture, released later that same year.
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.
A horizontal shockwave is seen edge-on near the end of the 1996 film Independence Day, when the alien mother-ship is destroyed by a nuclear bomb.
The effect is seen twice in the 1997 Special Edition of Star Wars Episode IV: A New Hope during the explosions of Alderaan and the first Death Star. It is once again seen in the 1997 Special Edition of Star Wars Episode VI: Return of the Jedi during the explosion of the second Death Star. The 2007 Star Wars expanded universe novel Death Star explained the ring effect at Alderaan as the shadow of a hyperspace ripple from firing the superlaser at full charge.
The effect is also seen near the end of the 1998 film Armageddon, when the asteroid is split in half by a nuclear bomb.
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 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 the first 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. However, the Praxis effect was perpendicular to the trench in this shot, instead of on the same plane. 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.
- Plait, Philip (2002). Bad Astronomy: Misconceptions and Misuses Revealed, From Astrology to the Moon Landing "Hoax" (Google Books). New York: Wiley. p. 254. ISBN 0-471-40976-6. OCLC 48885221.
- Liefeld, Rob; Murray, Brian (w), Murray, Brian (a). "Strange Interlude" Supreme 1 (November 1992), Extreme Studios/Image Comics
- Reaves, Michael; Perry, Steve (2007). Death Star. Star Wars. Del Rey Books. p. 342. ISBN 978-034547743-9.