Wizard of Id

"I hear the Huns are sending a man to the moon" says Rodney.
The Huns were a nomadic people who existed in the fourth and fifth centuries CE. Rodney is a medieval knight, probably from somewhere between the 12th and 15th centuries. Manned space flight first became possible around the middle of the 20th century. Hold up though, I bet all these anachronisms are going to lead somewhere. There's already a lot happening here and I can feel that this joke is going to have a pretty impressive pay-off.

"I want our space program cranked up immediately!" says the king.
There's never been any mention before of an Idiot space program, but presumably it's been happening quietly in the background.

Panel three takes us to a field. A man holding a purple flag with "ID" written on it is in a cannon.
"You want me to plant this where?" he asks.
"Just focus on your tuck and roll upon landing" says Rodney.
The first known cannon-like weapon was developed in China in the 12th century, but it was not in use in Europe until the 13th. This fits quite well with Rodney's time-line, except for the small detail of the nature of the projectile. The "human cannonball" did not appear until the 19th century.

And that's the joke.

Wizard of Id, 2013-09-12.