Question

many of the stars in the sky is¹ are² no longer as bright as they appear to us now.
option 1: is
option 2: are

Explanation:

The subject of the clause "Many of the stars in the sky" is "many" (referring to stars, a plural noun), so the verb should agree with a plural subject. "Are" is the correct plural verb form, while "is" is singular and incorrect here.

Answer:

Option 2: are