Of course it’s this year. Come New Year’s Eve, 2016 will linger for one extra second to make sure our clocks align with Earth’s rotation. Because each day actually takes 86,400.002 seconds, we add an extra “leap” second every so often. It won’t interfere with the ball drop in the U.S., as it will occur at 6:59:59 p.m. Eastern. And scientists can’t yet tell when the next one will be needed, because Earth’s rotation goes through subtle changes based on factors such as tides and melting glaciers.