Determine whether the boldface prepositional phrase is adjectival or adverbial

Question

The stars are twinkling in the night sky
1 adjectival phrase
2 adverbial phrase

Answer 1

1. adjectival phrase - "in the night sky" describes the stars and tells us where they are twinkling.

2. adverbial phrase - "in the night sky" describes the action of twinkling and tells us where the stars are twinkling.