Factual errors: A lunar eclipse can only occur when the moon is completely full, not gibbous as shown in the movie. Also, a lunar eclipse would not cast a moving shadow.
Factual errors: Frank changes stations on his neighbor's radio using the volume knob.
Factual errors: In the scene of the lunar eclipse, the moon shown is actually a mirror image of the actual moon. In a later scene, showing clouds beginning to cover the moon, the moon is shown normally.
Anachronisms: The ship entering New York at the end of the movie has radars. Radars were not available at that period on commercial ships.
Anachronisms: The newsreel shows German troops reoccupying the Rhineland in 1936. When middle Frank was watching the newsreel, he was 10 years old and therefore the year would be 1940, when Germany were occupying most of Europe and WWII was a year underway.
Anachronisms: The Statue of Liberty is shown with the solid, gold-plated flame (installed in 1984) instead of the old multi-paned lighthouse flame that in place during the timeframe of this film.
Revealing mistakes: When Frankie gets the beginnings of conjunctivitis, and he rolls his eyes back, you can see the edges of the full-eye contacts used to simulate the ailment.
Revealing mistakes: As Frankie McCourt cycles to the sanatorium to visit the stricken Theresa, a television aerial can be seen on the roof of the building. RTE, the Irish TV broadcaster, didn't start transmission until 1961.
Errors made by characters (possibly deliberate errors by the filmmakers): Young Frank does not have a cleft chin, teenage Frank does, and in real life Frank McCourt has no cleft chin.