Why does the sky appear dark instead of blue to an astronaut?

Explanation

During sunrise the light rays coming from the sun have to travel a greater distance in the earth.s atmosphere before reaching our eyes in this journey. The shorter waves of light are scattered out and only longer wavelengths are able to reach our eyes. Since blue colour has a shorter wave length and red colour has longer wave length the red colour is able to reach our eye after the atmospheric scattering of light, therefore the sun appears reddish early in the morning.
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 reaches the eyes of the astronauts. Without scattering the sky appears black to them.