Naked-Eye Particle Physics
By Kate Becker
Cosmic rays sound like something out of a superhero comic: invisible, traveling close to the speed of light, they are constantly shooting toward (and through) Earth from outer space. But they are real—and with a little know-how, you can see them for yourself, no superpowers required.
Despite their name, cosmic rays are actually particles. Mostly protons and helium nuclei, they also include a grab bag of heavier atomic nuclei. When they collide with atoms in Earth’s atmosphere, they set off a shower of “secondary” particles that rain down on Earth.