(I work in the astronomy section of my local natural history museum, which features several large NASA photos. A visitor approaches me and points at a picture of an astronaut doing a spacewalk.)

Visitor: “What is that astronaut doing?”

Me: “Oh, he’s doing a spacewalk.”

Visitor: “You can walk…in space?!”

Me: “Well, no. They just sort of float there while tethered to the spacecraft. They only do it when they need to exit the shuttle to do repairs.”

Visitor: “Oh…” *points at a photo of Apollo 11 launching* “What’s that?”

Me: “That’s Apollo 11 launching to put the first humans on the moon.”

Visitor: “Oh…why didn’t they just build a big ladder?”