What does 'dimmed the stars for a great arc' mean.
The moon was halfway up and dimmed the stars for a great arc.
A Wrinkle in Time by Madeleine L'Engle
It's saying that the moon was so bright the stars appeared dimmer along a whole arc of the sky. An arc is an portion of the circumference of a circle, which would of course be just a line, so I imagine it's referring more to a sector of the sky really.