What Is a Leap Second?

Why is June 30 the longest day in three years? Because you'll get one extra second in your day—a leap second. The International Earth Rotation and Reference Systems Service adds a leap second every few years to keep the clocks we use to measure official time and the speed of Earth's rotation in sync. But why do we need to do this? And what kind of problems could result?

Click here to read more about the leap second