Learn Hardcore Japanese: hiru no sora ni kumo ga ooi to, hosi ha miemasen. - When there are many clouds in the daytime sky, stars cannot be seen.

昼の空 literally means “the sky of the daytime,” or more naturally “the daytime sky.” The particle の links 昼 (daytime) as a modifier of 空 (sky), showing that the sky in question is specifically during the day.

Why is the particle に used after 空 instead of で?

Here に marks the location where clouds exist or accumulate. With existence expressions (like adjectives of quantity such as 多い) you use に to indicate “in/at that place.” So 空に雲が多い means “there are many clouds in the sky.”

Why do we say 雲が多い rather than 多い雲?

雲が多い is a predicate structure meaning “there are many clouds.” You use noun + が + 多い to express that many of something exist. By contrast, 多い雲 would simply describe “clouds that are many,” which is unnatural—you’d only use that if you were, say, contrasting types of clouds (“the many clouds” vs. “the few clouds”).

What function does と have in 雲が多いと?

と here is a conditional particle meaning “whenever” or “when.” It indicates an inevitable consequence: “When there are many clouds, (then) …” In this case the consequence is that stars cannot be seen.

Why is the verb 見えません used? Isn’t it a passive or potential form?

Actually, 見える is an intransitive verb meaning “to be visible” or “can be seen.” It’s not the passive or potential of 見る. So 見えません simply means “(they) are not visible” or “(you) cannot see (them).”

Why is 星は marked with the topic particle は instead of が?

Using は marks 星 (stars) as the topic of the sentence, focusing the statement on stars: “As for stars, …” It contrasts stars with other things you might see, and sets up the comment that stars can’t be seen under these conditions.

There’s no subject like “you” or “we.” Why is that omitted?

Japanese often omits subjects when they’re clear from context. Here it’s a general statement about what happens—“(people) can’t see stars.” The speaker assumes a general audience so no explicit pronoun is needed.

Is the comma after と necessary?

In writing, the comma (、) simply shows a pause and separates the conditional clause from the main clause. It isn’t grammatically required, but it makes the sentence easier to read.