Image zoom Credit: Getty / Aaron Foster On July 19, 2020, the day was 1.4602 milliseconds shorter than the full 24 hours—the shortest day since scientists began keeping records in the 1960s. Similar to leap year, timekeepers at the Paris-based International Earth Rotation Service have added what's known as so-called "leap seconds" to a total of 27 days since the 1970s, the most recent one occurring on New Year's Eve in 2016. Those few extra seconds help satellites and communications equipment accurately align with solar time, which is determined by the positions of the stars, moon, and the sun. So, what exactly is causing this to happen? A 2015 study published in