It's not something that's immeditately apparent when you hear it, but the most famous "Hedwig's Theme"
from Harry Potter owes a lot to Celtic folk music, and traditional songs like Greensleeves or
Scarborough Fair. In particular the rhythm found in the opening bar:
Follow the links to Greensleeves and Scarborough Fair above and you'll see they both use the same rhythm of dotted quarter note - eighth note - quarter note in a 3/4 bar.
They also use a half-note, quarter note which is also found in the Harry Potter theme.
To show you the similarity a bit more, here, for example
is a tune I've just invented, which uses those five notes as a starting point, but sounds much more like a folk tune.
One of the main reasons the Harry Potter theme sounds so different is the instrument it's played on - a keyboard instrument called a celeste.
To prove the point, let's hear my tune again with a celeste sound.
That's much more spooky, right?!
For more Harry Potter, have a look at the first page of Diagonal Alley, courtesy of our friends at sheetmusicplus: