Question

the sky appear Blue on earth but dark on moon

Answer 1

The Moon's atmosphere is negligibly thin, essentially vacuum, so its sky is always black.
Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere.Blue is scattered more than other colors because it travels as shorter, smaller waves.

Answer 2

Explanation:

The sky appears dark instead of blue to an astronaut because there is no atmosphere in the outer space that can scatter the sunlight. As the sunlight is not scattered, no scattered light reach the eyes of the astronauts and the sky appears black to them.