Is there a word which describes being unable to see the stars because of the brightness of the moon?
You can say that the stars are washed out by the moonlight:
intransitive verb
- to become depleted of color or vitality: fade
Unlike obscured, which to me has a connotation of either covering, physical obstruction, or darkness, washed out paints a more appropriate picture, which is that there is too much light.
Obscured
Meaning (verb past tense): keep from being seen; conceal.
Example(s): The stars were obscured by the brightness of the full moon. You might well wear sunglasses to prevent the glare of the sun from obscuring your view.
Synonyms: hide, conceal, cover, veil, shroud, screen, mask, cloak, cast a shadow over, shadow, envelop, mantle, block, block out, blank out, obliterate, eclipse, overshadow
Seems to fit the purpose?