Italy's first post-WW2 science fiction film (and third overall after 1910's 'Matrimonio interplanetario' and 1921's 'The Mechanical Man') begins with a malfunction on an atomic rocket heading to the moon. The astronaut (Paul Hubschmid) evacuates the ship in an emergency capsule but does not shut off the ship's atomic engines, which eventually explode, causing an asteroid cluster to coalesce into a single mass that ends up on a trajectory towards Earth. Despite being partially shielded by the moon, the rogue asteroids cause calamitous changes in the environment and, if they cannot be diverted or destroyed, will ultimately destroy the planet. The film is not particularly good (although the grainy, poorly dubbed version I watched may not have done the original justice). After some promising special effects (for era and budget) at the rocket base, the film devolves into talky sequences in cheap-looking sets, a time-filling subplot as the strangely inexpressive astronaut has a stress-induced martial crisis, and extensive use of stock footage. Cinematography was by Mario Bava (who is sometimes given directing credits as well) and while there were some interesting, moody shots, they don't raise the film above mediocre. 'The Day the Sky Exploded' is more of interest for its primal place in the history Italian science fiction cinema than as standalone entertainment (and even then, Antonio Margheriti's "Space Men" (1960) makes a much better introduction to spaghetti space-operas).