Factual error: The sun can't rise out of the Pacific ocean when viewed from America, as seen when Danny is playing the clarinet. (00:01:20)
Factual error: In scenes that take place in 1912 on the porch of the hotel you can sometimes see American flags in the background. The flags in the movie have 50 stars. The 50 star flag wasn't adopted until after 1959. (01:25:15)
Factual error: After Superman accidentally frees the phantom zone villains with the exploding hydrogen bomb, they start flying towards the moon. The sleeves in their clothes can be seen fluttering around. This would be impossible because there is no air in outer space, hence nothing to cause resistance against the clothes.
Factual error: A solid gold cross of the size used in the film would weigh more than what any human could hold in front of them (nearly 200kg), much less as "easily" as the priest did at the end of the movie.
Factual error: There are three major mistakes regarding gravity in the escape sequence in the asteroid field. Han and Chewie take the Millennium Falcon to refuge on an asteroid that, while visually huge, is still far too tiny to have sufficient gravity to allow humans to walk in anything like a normal fashion; yet, they walk normally both inside and outside of the ship. They also do not use pressurized suits outside of the ship, even though the asteroid's gravity should be far too weak to accumulate any significant atmospheric pressure; they use oxygen masks, but their blood should have boiled in near-zero atmospheric pressure. Finally, and most ridiculously, they fly straight down the giant cave worm's throat and land on the side of its throat (this is obvious in the shot where the Millennium Falcon lifts off and heads toward the toothy exit), and they get out and walk around on the side of its throat, which would mean the asteroid's gravity was impossibly perpendicular to its mass. (00:57:50)