Continuity mistake: In the end when they shoot off their last rocket, there is a blue sky with a few scattered white clouds.after the launch when everyone is watching the rocket, there are heavy storm clouds, then it cuts back to a clear blue sky again.
Continuity mistake: At the end, when John puts his hand on Homer's shoulder, Homer looks left and down. In the next shot, he's instantaneously looking at John.
Continuity mistake: Near the beginning, just before the town sees Sputnik at night, Roy Lee is talking to Homer about seeing a movie with a date. Homer is looking up at the sky. The shot cuts and he is looking forward. (00:07:55)
Continuity mistake: In the first shot of the train scene there is no turn off track but in the next shot one appears outta nowhere. Hell it's even in a different spot judging by the lack of shrubbery in one of the shots.
Factual error: As Homer and his friends attempt to flag down the train after dislodging the old rail, the engine seen is of the 2-8-2 wheel arrangement with markings of the Norfolk and Western Railway. The Norfolk and Western never owned any 2-8-2 locomotives, preferring instead engines of the 4-8-0 arrangement.
Other mistake: Throughout the film, the Hickams' phone buzzes. When Elsie throws the phone into the yard, it breaks to reveal a pair of bells.
Factual error: This movie takes place in 1957, clear from the Sputnik reference, but at the dance they play "It's All in the Game" which didn't come out until 1959.