08 September 2006
During space flights they see pinprick flashes of light streak across their field of vision when they close their eyes. Not a lot, and not all the time, but often enough that they report it. They are seeing cosmic radiation; tiny particles from distant stars have traveled for millions of years to pass through their eyeballs. Think of it. Astronauts have their own private mini planetariums, swiveling around in their skulls. Back on the ground, the absence of the streaks is a reminder: above the atmosphere, there’s nothing to protect you. Air is all we have for our ultimate defense.