Defining a nanometer may be easy: One meter equals one billion nanometers. But it isn’t as easy to picture how small a nanometer really is. The first step can be to try imagining a billion of something. If you asked a billion girls to stand on each other’s shoulders, they would stretch into space two-and-a-half times farther than the Moon. Another way is to imagine a billionth of something big. If you sliced the world’s tallest building a billion times, each slice would be thinner than the red blood cells you see through a microscope. Nano is even smaller than that. And, because it’s so small, nanotechnology can influence atoms and molecules in strange ways.