NASA’s Jet Propulsion Laboratory has just released a fantastic explainer video about why astronauts appear weightless in space, even though they are still subject to Earth’s gravity. This latest video employs the help of Alan Tudyk, voicing a parasite inside Wil Wheaton’s brain. It’s quite good:

As the video explains, astronauts are never really weightless in space, they just appear that way relative to the ship or craft they are in. If we could zoom out far enough to see both the whole Earth and an orbiting astronaut, for example, we would see that they are indeed falling around the Earth and not floating. Every orbiting thing in the universe is falling around something else. “Every body in the universe is always falling towards something,” Tudyk’s parasite explains. “And if it doesn’t feel like you’re falling, that’s because you’re standing on something that is falling.”

NASA/JPL’s “Irrelevant Astronomy” series has had geek heroes in its science videos before. A few months ago, Ellen McClain–the voice of GLaDOS from the Portal series–voiced another Irrelevant Astronomy episdoe about the difference between nuclear fission and fusion.

By the way, there are such things as brain parasites. This one–a brain-eating amoeba–even has a “face,” which might in fact make you do this: