Cloud Chamber Exhibit at the Exploratorium

My new favorite exhibit.
...A chamber is filled with supersaturated, supercooled alcohol, so it is just at the point of condensation. When high speed charged particles ('cosmic rays') interact with the chamber, the paths they trace become ionized and act as condensation nuclei for the alcohol, creating momentarily visible "cloud" trails. It's a bit like watching shooting stars. Cosmic rays are subatomic particles that are so small they penetrate through buildings, rock and people. They reach Earth at about one particle per square centimeter every minute. Ninety percent are protons (mostly helium, but also some heavier elements), and a small percentage are electrons. They can originate from our sun, supernovas across the galaxy, the big bang, or other cosmic events.