A spark chamber is a device that allows the visualization of tracks made by subatomic charged particles, such as muons created by cosmic rays colliding with Earth’s atmosphere. Spark chambers work by creating a large high voltage between plates. When a particle goes between the plates a spark is created along the path of the track.
In the video above you can see the spark chamber, built by Georgia Tech undergraduate students, in operation. The red sparks indicate the passage of a down-going muon. This muon was created 10 to 20 km high in the atmosphere and is the product of the collision of a cosmic ray with an oxygen or nitrogen nucleus.