Blue Skies

I was reading a magazine the other day and found the phrase, "beautiful skies over Berlin." We say "beautiful skies" or "blue skies," but how can we pluralize the word "sky"? In my understanding of this universe, there is only one sky. How do you count skies?

I mentioned this in one of my earlier posts, but I feel that the English language is inconsistent when it comes to what can be counted and what cannot be counted (countable and uncountable nouns). For example, the word "advice" is uncountable, but the word "suggestion" is countable.

Ex.
That's good advice!
That's a good suggestion!

Is there a logic behind this categorization? To me, if "advice" is uncountable, "suggestion" should also be uncountable.