When a star explodes or the Sun erupts in a flare, protons and electrons are blasted away as cosmic rays. They travel across space at high velocities and constantly bombard Earth.
Cosmic rays collide with gas molecules in our upper atmosphere. They shatter to create muons and other particles that rush to Earth’s surface. We can detect some of those “secondary” cosmic rays using cloud chambers.
How a Cloud Chamber Works
A cloud chamber shows the tracks of secondary cosmic rays that reach Earth’s surface, mostly from space. The chamber contains alcohol vapor cooled to become “supersaturated.” When high-speed charged particles pass through, they knock electrons off neutral atoms and air molecules, which become charged. The alcohol vapor condenses onto the newly charged particles, and we see long thin “clouds” along their flight paths.