This is simultaneously cool and horrifying. Cosmic rays are actually particles—tiny protons and neutrons, that shoot through space. They’re too small to see, but astronauts may still be seeing them.
Radon is dangerous mostly because we don’t notice it. We can buy detectors, but we’re not equipped with any of them. The gas is colorless, odorless, and tasteless. You can’t see it... because it’s too hot. As radon cools down, it starts to glow. And it’s tough to say why.
When a plane goes faster than the speed of sound, those around it hear a resounding crack that's called a sonic boom. When particles go faster than the speed of light, those around them see a special glow. This is called Cherenkov Radiation. And it's a lot prettier than a sonic boom.