as promised, the expatiation of the number of stars that appear on US flags in the movies.
The number of stripes is a given; it's always 13; the count of the original colonies that formed the United States. (I'm going to ace that citizenship exam ).
The number of stars varies according to the era. You'll notice that M*A*S*H always shows the 48 star flag because, even though the series was made in the 1970's it's set at the time of the Korean War when there were only 48 states.
So much is obvious.
I take a perverse delight in comparing the number of stars shown on the US flag to the time in which the movie is set. For instance, in Tommy[^] there's a scene right at the start of the film where they're celebrating the end of WW2. The camera pans across a vista of flags (I note that the Australian flag is shown reversed - tut tut ). The US flag has 50 stars. Someone didn't do their research.
In The Patriot[^] they're very careful to show the 13 star flag with the stars arranged in a circle whenever you see the flag in closeup. But during the long shot battle scenes if you look really carefully you can see that the stars on the US flags are arranged in a rectangular array. Given that the movie was made in 1999 (released in 2000) I'd bet those flags have 50 stars.
In Gangs of New York[^] the number of stars varies. As far as I can tell the variation follows the admission of new states into the union. Certainly as time passes the number of stars increases.
And so I started to wonder. If Alaska became the 49th state on January 3, 1959 and Hawaii became the 50th state on August 21, 1959 what happened to flags in the movies during that time. It's somewhat complicated by the fact that the flags didn't change on those dates. I quote the following text[^].
'Following Alaska's admission in January, 1959, a new flag with 49 stars was designed and first flew over Independence Hall in Philadelphia on July 4, 1959. It would be the official flag for only a year. The 50 star flag became the 27th flag on July 4, 1960, and remains the official flag of the United States.'
So far I've only found one movie that shows the 49 star flag and that movie is On the Beach[^].