hiru no hizasi ga tuyokatta node, kouen no kokage de yasumimasita.

Here の links two nouns, so 昼の日差し means something like the sunlight of midday / daytime sunlight.

• 昼 = daytime, noon
• 日差し = sunlight, sun’s rays

So 昼の日差し is a noun phrase. It describes what kind of sunlight it was.

If you used に instead, it would not make the same noun-modifying phrase. の is the natural particle here because 昼 is acting like a descriptor for 日差し.

Not exactly.

• 太陽 = the sun itself
• 天気 = weather
• 日差し = sunlight, especially the sunlight shining down on you

日差し often suggests the strength of the sun’s rays and how they feel. So in this sentence, it fits very well with 強かった because the idea is that the sunlight was intense.

が marks 日差し as the subject of 強かった.

So the structure is:

昼の日差しが強かった
= the midday sunlight was strong

The thing being described as strong is 日差し, so が is the natural particle.

It is in the past because the sentence is telling a past event as a whole:

• the sunlight was strong
• so the speaker rested in the shade

Japanese often uses the past tense in both parts when describing a completed situation in the past. It does not necessarily mean the sunlight stopped being strong before the resting happened; it just means the speaker is narrating what the situation was at that time.

Both ので and から can mean because, but ので usually sounds a little:

• softer
• more explanatory
• more neutral or polite

So:

• 強かったので = because it was strong
• 強かったから = also correct, but can sound a bit more direct or personal

In a calm narrative sentence like this, ので sounds very natural.

影 means shadow in a broad sense.

木陰 specifically means the shade of a tree / shade under a tree.

So 公園の木陰 gives a very specific image: a shady spot under a tree in the park. It is more natural and vivid than just saying 公園の影 here.

Again, の connects two nouns.

公園の木陰 means:

• the park’s tree shade
• more naturally, the shade of a tree in the park or a shady spot in the park

It tells you which shade: the shade associated with the park.

で marks the place where an action happens.

Here, the action is 休みました = rested.

So:

• 木陰で休みました = rested in the shade

Compare:

• で = where an action takes place
• に = destination, existence, specific point in time, etc.

Because resting is an action happening at that location, で is correct.

休みました simply states that the speaker rested.

It is a straightforward past action.

休んでいました would mean something more like:

• was resting
• had been resting

That form focuses more on the action being in progress or on the state during a period of time. In this sentence, the simpler 休みました is enough because the speaker is just reporting what they did.

Japanese often leaves out the subject when it is clear from context.

In this sentence, 休みました strongly suggests that the speaker is talking about their own action, so English would usually supply I:

I rested in the shade of a tree in the park because the midday sunlight was strong.

This omission is very normal in Japanese.

It can suggest either, depending on context, but here it most naturally points to daytime / midday sunlight.

昼 often refers to the daytime period, especially around noon. In this sentence, the exact clock time is not the main point. The important idea is that it was the sunny part of the day, and the sunlight was strong.

Yes, this is a very common Japanese pattern:

reason + ので / から, result

So:

昼の日差しが強かったので、公園の木陰で休みました。
= Because the midday sunlight was strong, I rested in the shade of a tree in the park.

Japanese often puts the reason first and the main action second. This is very natural and common.

Yes. The plain-style version would be:

昼の日差しが強かったので、公園の木陰で休んだ。

Changes:

• 休みました → 休んだ
• the rest can stay the same

The original sentence is in polite style because of 休みました. That makes it suitable for normal conversation or written explanations in polite Japanese.