Calendars & Music

Leap years and 12 notes

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Leap year rules approximate 0.24219 with convergents like 1/4 and 8/33.
• The Julian calendar drifts a day every 128 years.
• The 12-note scale comes from the convergent 7/12 of log₂(3/2).

Steps

1. Fitting days into years
2. Drift of the Julian calendar
3. The Gregorian fix
4. Most accurate rule
5. Why 12 notes?
6. Better scales