Astronauts

Astronauts Can Actually See Cosmic Rays

Here on Earth, it's tricky to detect cosmic rays, the high-energy particles that regularly blast through our solar system from other galaxies or our own sun. But in space, it's easy. Astronauts regularly see them with their naked eyes.

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Dangerous Apparitions

The first person to report seeing cosmic rays was none other than Buzz Aldrin. During the Apollo 11 mission in 1969, he mentioned seeing strange flashes of light that took on a variety of shapes and dimensions. When astronauts say they're seeing things, people take them seriously, so by the time Apollo 16 and 17 took off there was a special detector on board to figure out what was going on. The results? The flashes were caused by high-energy charged particles, the stuff of cosmic rays. Over many more missions, the research continued, showing that the particles affected every astronaut differently: some could see them in bright conditions while others could only see them in the dark; some were so bothered by them that they had trouble sleeping while others couldn't see them at all.

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Here's the problem: cosmic rays aren't just sci-fi jargon. They're really harmful. Specifically, they're radioactive fragments of atoms—mostly protons, but also some neutrons and electrons—that move at incredibly high speeds and tear through any molecules unlucky enough to be in their path. They're the reason radiation is a primary concern on future missions to Mars. The fact that astronauts are seeing them means that cosmic rays are hurtling into astronauts' eyes. Not good.

Why Can Astronauts See Them?

We know the flashes are cosmic rays, but we don't actually know the reason astronauts are seeing them. The rays aren't light, after all—they're just radioactive particles. Researchers have formed three theories about why astronauts can see them: one was that they were entering the eye and hitting the optic nerve. Another was that they were entering the astronauts' skulls and hitting the vision center of the brain.

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The third theory is definitely scariest: the particles are traveling through the vitreous humor of the astronauts' eyes and emitting light in the form of something called Cherenkov radiation. As io9 puts it, "The light is coming from inside their eyeballs."

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