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.
You can’t see these subatomic particles directly, but using a cloud chamber, you can make their paths visible to the naked eye. In this video, NOVA’s Greg Kestin shows how to create your own cloud chamber at home.
In this video, see stunning cloud chamber video of subatomic particles streaming off a radioactive rod.
Researchers now think that most cosmic rays come from supernova explosions, but the sources of very rare, ultra-high-energy cosmic rays, which carry energy that far exceeds anything produced at experimental particle accelerators like the LHC, are still a mystery.
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CERN: Cosmic rays: particles from outer space
Get acquainted with the basics of cosmic rays in this primer from CERN.
Nature: To catch a cosmic ray
The Pierre Auger Observatory in Argentina has observed dozens of ultra-high-energy cosmic rays, but their source remains a mystery. Nature News’ Katia Moskovitch asks what’s next for the observatory.
Pierre Auger Observatory: The mystery of high-energy cosmic rays
What are high-energy cosmic rays, and where might they be coming from?