And Luna makes a ton of sense if you want to remove the ambiguity of a moon and the moon.

Right? I can't think of any scifi that refers to the sun as helios?

And moon is called Luna

That's why an orbit around the sun is "solar" and an orbit around the moon is 'lunar"

It seems like earth is just called earth for most spaceflight purposes (e.g. low-earth orbit), although the word for it in some Latin languages comes from "terra"

I think it'd be fun to call earth "Humus". We get words like posthumous, exhume, humility from it, and it's theorized that it may share an origin with the word Homo, from which we get "Human".

So if we called it Earth we'd be Earthlings, if we call it Terra we'd be Terrans, if we called it Tellus we'd be Tellurians, but if we called it Humus we could stay as Humans =D

Originally it was called Jimmy though.