Oftentimes you'll see the Moon (Earth's moon) called "Luna" as well, although this is more understandable since "moon" (lower case) has become a term for any natural satellite of a planet—so using "the Moon" (even capitalized) could invoke the question, "which moon?"

Somewhere I've encountered an alien who's amused at "a planet named after the dirt"—i.e., Earth. That's got to bear some relation to this, no?

Assuming anybody can identify the work—or, I somehow think, series.

Thx.