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Cosmic Rays

© TRACE (Standford-Lockheed Institute for Space Research/NASA)

Every moment of every day, the universe reaches out and touches us with cosmic rays. They come from stellar explosions, black holes, and even our own Sun. These particles dash across space at close to the speed of light. They move easily through matter, including our bodies.

Cosmic rays shatter air molecules high in our atmosphere and send atomic and subatomic particles showering down on Earth. We can measure the presence of these tiny, unseen visitors with special devices that record their paths as they rush past us.

Cloud Chamber

© Anthony Cook, Griffith Observatory

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.

© Anthony Cook, Griffith Observatory   image of how it works.

Spark Chamber

© Anthony Cook, Griffith Observatory

Cosmic rays are not rays, but high-energy particles from space. When they collide with gas molecules in our upper atmosphere, muons and other "secondary rays" are created. These constantly shower down to Earth's surface.

Dozens of those secondary cosmic rays pass through our bodies every second. We can detect them when they go through a spark chamber and cause electrical disturbances.

How a Spark Chamber Works

A spark chamber detects energetic particles (mostly muons) that pass through it. When these particles encounter the helium and neon gases inside, they ionize the atoms of gas (by stripping electrons away from their atoms). If a particle hits all three sensors, the high-voltage plates become electrified. We see and hear sparks created along the particle's ionized path where it intersects the plates.

© Anthony Cook, Griffith Observatory   image of how it works.