When is 的 needed to express "of"? Consider the following two sentences:


早晨的太阳为什么是红色的
中午太阳又变白了


For the first sentence: the second 的 is because 红色 is 区别词 and the first 的 expresses alienable possession (i.e. no close possession).

But in the second sentence: there is no "的" after "中午" as I would expect. Why?

I also found the following sentence: 你还得提高教育质量. In English, I would say "quality of education" and not "quality education". Hence, I would also expect a "的".

Another difficult case is "科学模型" vs "科学的模型".

Can somebody clarify how to use "的" to express "of"?
早晨的太阳为什么是红色的
中午太阳又变白了

中午的太阳又变白了 is a correct sentence. But, if you put that 的, you'd change the parsing:

[中午的太阳][又变白了] vs [中午][太阳又变白了]

The original sentence uses 中午 adverbially, which is for the effect of contrast: Why the sun in the morning is red, while at noon(when it comes to noon) it becomes white.(I'm curious how come).
中午的太阳又变白了 would reduce that effect dramatically.
So, the question here is not about grammar but the way people express their ideas.
P.S. I might think to add a comma after 中午 would probably be a little bit improvement? Maybe, not everyone would agree with that.

早晨的太阳为什么是红色的
中午, 太阳又变白了