The Linguistics of the Moon.
In my wife’s science fiction series there’s some action involving the Moon . . . or is it the “moon?”My wife raised the question of whether “Moon” is capitalized. My off the cuff answer was that it is, if you are talking specifically about Earth’s Moon, but not if you are speaking generically about a moon.
Not satisfied with my guess she tasked me to research the question, she is very detailed oriented and wanted to get right. This appears to be among the most hotly disputed questions in the English language, with various websites providing different answers. Most the different answers fall in three categories.
1. Planets names are all capitalized with the exception that earth, sun and moon are never capitalized. It just seems wrong to me that you would say: “The earth is three times bigger than Mars.” But that actually seems to be the prevailing book answer, and the failure to capitalize “earth” suggests an inferiority to Mars.
2. The earth, moon and sun are not capitalized unless used in conjunction with one of the capitalized planets names. Thus “The earth is six times bigger than the moon” gets transformed if one throws in a planet to “The Earth is six times bigger than the Moon and three times bigger than Mars.” That seems a rather arbitrary transformation (note: some sites add to the arbitrary approach by claiming the moon is never capitalized, even when used with other capitalized celestial bodies so the prior sentence would be: “The Earth is six times bigger than the moon and three times bigger than Mars.”). Let’s just label that approach 2b.
3. Much as I suggested above, when used as a proper noun to refer to our particular Moon (aka Luna), or our particular planet (the Earth we all live on) or the particular Sun around which our Earth orbits, it is capitalized. If used generically it is not capitalized. Examples might include: “Our Earth certainly contains much earth” or “Our Sun is but one of many suns” or “Our Moon is in many ways different from most other moons in the solar system.” Frankly, this minority approach is the one I think should be it. It follows the general rule that proper nouns are capitalized, it provides a consistent rule for treating our Earth equal to the names of other planets, and offers the benefit of providing a signal to the reader of whether you are using the word generically or specifically.