If you’re a music lover, you may have heard of the so-called “Tristan chord” from Wagner’s opera Tristan und Isolde. Audiences were stunned to hear this infamous harmony when the opera premiered on June 10, 1865 in Munich, Germany. As Tristan turns 150, let’s take a look at what makes the Tristan chord so unique. The “Vorspiel,” or Prelude, to Tristan begins with with a “dissonant” chord. The terms “consonance” and “dissonance,” “music” and “noise” are largely subjective. Now, in an era where our ears can enjoy everything from Chopin to Chick Corea, what our modern ears hear as “consonant”...