June 30 will be 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. The addition will mean that the last minute of June will have 61 seconds; while 23:59:59 usually becomes 00:00:00, the leap second will ensure the time becomes 23:59:60. How will you spend your extra second today? Check out this video by National Geographic for more information about the “leap second”!