Answer:
Moon's matte surface that makes it less reflective and the variation in the amount of sunlight received by the Moon at the edges.
Step-by-step explanation:
The key reason for the bright rays on the Moon's surface becoming duller is the matte surface of the moon which does not allow the rays to reflect properly and appear brighter. The other reason is the variation in the amount of sunlight that the Moon receives at the center and towards the edges and the matte surface makes the light scatter in different directions instead of reflecting in the d bright direction(as in a mirror) and thus, it appears duller.