Since 1972 there have been 27 leap seconds: additional seconds added to the world’s common clock — Coordinated Universal Time or UTC — to account for changes in the Earth’s rate of rotation. Historically, our concept of time is defined as a fraction of the length of the solar day, but as the Earth’s rate of spin is somewhat irregular (slowing and speeding based on various factors) it means solar time and universal time tend to drift apart. So, in order to compensate, we add leap…