"...Earth is no longer accelerating its rotation. But it is still spinning at a quicker rate than average." by Stephanie Pappas via LiveScience Headline Image Caption/Credit: Star trails over Alberta, Canada, captured as the Earth spins at night. Earth's rotation has settled down since 2020. (Image credit: Nick Fitzhardinge via Getty Images) After speeding up during 2020, Earth's rotation has settled down. But timekeepers say we still may need a "negative leap second" in the next decade. On average, each Earth day contains 86,400 seconds. But Earth's rotation isn't perfect; it varies slightly all the time depending on the movement of the core, oceans and atmosphere. Universal Coordinated Time (UTC), the official international timekeeping method, is based on the atomic clock, which measures time by the movement of electrons in atoms that have been cooled to absolute zero. Atomic clocks are precise and invariable. So when Earth's rotation and the atomic clocks don't quite sync up,