I just came across the score for Beethoven's Moonlight Sonata, and I was surprised when I saw the time signature of the first movement.
(My background is that I've played music for many years—mainly guitars and keyboard—but not studied music theory beyond what was covered in piano lessons as a child. So I have a basic understanding of time signatures, note values, triplets and suchlike, and am used to working with them. Although while the C-shaped time signature symbol means 4/4 or Common Time, I did have to search to learn that the vertical line through it means either tempus imperfectum diminutum or Alla breve.)
My surprise came when I saw that the movement is written in 4/4 (or is it 2/2?), with the melody as triplets across it. Without really thinking about it, I had assumed it would be in something like 6/8.
Previously, I've only encountered triplets as occasional exceptions that bring a certain emphasis to short sections by their contrast. Yet here, triplets are the norm for the entire movement. What is going on here?