One of the more endearing—and frustrating—aspects of the human brain is its ability to hold two completely contradictory notions at the same time. Each idea seems fine on its own, but then when you put them together, you get what’s called cognitive dissonance: ideas that conflict. That sometimes leads to greater insight, if it can be resolved.
One of the more popular examples of this when it comes to space science are the two seemingly antagonistic ideas that a) gravity goes on forever, and 2) astronauts are weightless in space. How can both of these things be true?
The answer is: motion. I could explain, but instead you should just watch this adorably animated video by the folks at the Spitzer (Space Telescope) Science Center, as part of their wonderful IRrelevant Astronomy series. After all, if you’re going to learn space science, why not learn it from the brain parasite of a scientist played by Wil Wheaton?
If the voice of the brain parasite is familiar, it’s because it belongs to beloved-by-geeks actor Alan Tudyk (Wash from Firefly). And his explanation is right on the money: Gravity does go on forever, but the sideways motion by astronauts keeps them in free fall.
These videos are really good, and really funny (by the way, it’s "IRrelevant Astronomy" because Spitzer detects infrared light, commonly abbreviated as IR). You should watch more. Many feature famous actors, and they’re truly delightful. I’ve written about several, listed below. You might also like an amazing video taken inside the International Space Station during an orbital boost, which shows a fun effect of motion.