On Earth, gravity constantly pulls fluids in your body and your brain toward the center of the Earth. In space, that force disappears. Body fluids shift toward the head, which gives astronauts a puffy face. Under normal gravity, the brain, cerebrospinal fluid and surrounding tissues reach a stable balance. In microgravity, that balance changes.

The International Space Station passed over the Valley Monday afternoon, giving 500 students at Canfield's Hilltop Elementary School the chance to talk to a real astronaut -- live from space.

Here's a look at the science experiments on board.