On: The moon is not the Earth’s only natural satellite

[dijit]

that's not just Sci-fi, that's their actual names in latin, which means that's what's used in science.

Luna and Sol: Root origins of "Solar System" and "Lunar eclipse" etc;

[quarterto → dijit]

Well, yes, but they're not used as names in common speech, hence my point.

[ejk314 → quarterto]

I bet there's a word for that - using the more general term for something as a proper noun when the meaning is obvious from context. Like calling the largest nearby city just "The City". I figure it's the same general idea behind calling it "The Moon".

[innguest → ejk314]

Metonym?

[mturmon → innguest]

Also, synecdoche ("a figure of speech in which a part is made to represent the whole or vice versa")

[Shorel → quarterto]

'Sol' and 'Luna' are used as their names in common speech, every single day, in all Spanish speaking countries.

[quarterto → Shorel]

And this is a conversation about English common names and literature.