Imagine you could shrink down to a size smaller than a grain of sand. You would enter a world of atoms, the tiny building blocks of all matter. Niels Bohr, born on October 7, 1885, in Copenhagen, Denmark, helped us understand this hidden world. Scientists already knew atoms existed. But no one was sure how they worked on the inside. Bohr came up with a new model in 1913. He said that atoms have a center called the nucleus. Tiny particles called electrons travel in paths around the nucleus. Think of planets orbiting the sun. Each path holds a certain number of electrons. When electrons jump between paths, they give off light. This idea explained why different elements glow different colors when heated. Hydrogen glows red. Neon glows orange. Bohr won the Nobel Prize in Physics in 1922. His model was not perfect, but it gave scientists a way to picture the invisible. Today, students still learn the Bohr model as their first step into atomic science.