Choice of Words: Sky is the area above the earth. "Blue" is a color. "Vast" means very large or wide. "Above" means higher than something else.
Alternative Expressions
The sky is blue and big up there.
Meaning: This means that the sky is a big, blue space that is above us.
Choice of Words: The sky is the big, open space above us. Blue is a color that is often used to describe the sky. Big means that something is large in size.
Up above, the sky is a blue expanse.
Meaning: This means that the sky is a large, blue area that is high in the air.
Choice of Words: Up above means that something is high in the air. An expanse is a large, open area.
The vast blue sky stretches overhead.
Meaning: This means that the sky is very large and blue, and it stretches over a long distance above us.
Choice of Words: Vast means that something is very large. Stretches means that something extends over a long distance.