Well, Whadya Know

Why do we joke about fools believing the moon is made from
green cheese?

It's not just green cheese by default. Did you ever stop
to think, just what is "green cheese," after all? There's no
such thing, right? Literally, that's true. The "green" in
this old proverb refers to the quality of "newness."
Specifically it described a hunk of cheese that had not yet
aged, the appearance of which reminded people of what the
moon looked like from afar. But only a fool thought it was
really made from it.

[source: Dictionary of Word and Phrase Origins by William and
Mary Morris]

Why do they call that radioactive stuff "uranium?"

Uranium was discovered in 1789 by Martin Klaproth, a
German chemist, who named it after the planet Uranus.
Sir William Herschel discovered
and named Uranus a few years previously.

In fact, 150 years ago people were already practicing
radioactive medicine, treating everything from birthmarks to
ringworm with uranium. No wonder they're all dead! (hehe)

[source: The Secret Lives of Words by Paul West]