Question

why does the sky appear dark to astronaut

Answer 1

In space there is a vacuum, hence there are no particles to scatter light.

Thus the sky appears dark as blue light is not scattered.

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.