Surah 75. Al-Qiyamah, Ayah 9

I.e., in their loss of light, or in the moon's colliding with the sun.

 They both will rise from the west and lose their light.

To the moon the sun is the original light, but the sun itself is a created light, and it will sink into nothingness alongwith the moon. Both will be like empty shells "whose lights are fled, whose glories dead", because the Light of Allah now shines in full splendour in a new World. See n. 4344 to xxxix. 69.