In English, proper nouns are always capitalized. Since there is only one sky I would expect it to be a proper noun and capitalized. But it seems it is treated as a common noun and not capitalized. Why is this the case?
4'Sky' is a common noun because it is a general name for what we see when we look upwards. There is not a 'thing' there. Also there can be many skies. The night sky, the daytime sky, the winter sky, etc.– Michael HarveyApr 22, 2021 at 21:47
Thanks. If you put this as an answer I can accept. Makes sense to me– abirApr 22, 2021 at 21:50
Proper nouns are capitalised, but "sky" is not a proper noun.
Proper nouns name specific people, places, objects or concepts. And so for every proper noun, there should be a generic noun (or nouns) that name the type of that noun:
John is a man.
Paris is a city.
Wednesday is a day of the week.
But can you do that with sky?
Sky is a ....?
Moreover (as mentioned in a comment) "sky" isn't a single specifically named thing, as there is the "night sky" or "the daytime sky", or "a beautiful sky in Kansas" and so on.
Now, sometimes we use "majestic proper nouns". If a noun is a specially important it might be treated like a name. This is particularly common with nouns associated with God, or with common nouns used in place of names.
John is in Heaven now.
The Queen visited our factory.
The Universe formed 13.7 billion years ago.
But this would rarely be a justification to use "The Sky" as a proper noun.
Just to add a different perspective on this.
We talk about "the sun" or "the moon" but we also (perhaps poetically or pretentiously) also refer to Sol and Luna.
However, I don't know of any such "name" for the sky.
From what I’ve learned (and remember), proper nouns are usually names (of nouns) therefore “sky” is considered a common noun. An example would be the words “month” and “January”; “month” isn’t capitalized because it’s a common noun but “January” is because it’s a name of a month.
1Answers need to be definitive. Apr 23, 2021 at 0:33