The Earth's rotation doesn't line up perfectly with our calculation of it, so to keep things consistent, we have to adjust. That's why this weekend will have a leap second. This Saturday, just before midnight Greenwich Mean Time, clocks will count to 60 seconds, instead of 59.
How should you spend that free, unexpected single second? Here are nine ideas.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.