Leap Seconds

Did you know? What we experience as Coordinated Universal Time (or UTC) is an atomic time scale based on the performance of atomic clocks and more stable than astronomical time (or UT1), which is based on the Earth's irregular rotational rate. Whenever the difference between UTC and UT1 approaches 0.9 seconds, a “leap” second is added to correct for it. Learn more from the National Institute of Standards and Technology.