For an astronaut in a spaceship, the sky looks black due to:

• Light is scattered due to the presence of the atmosphere around the earth.
• Since the wavelength of blue light is the least among the visible colours, it gets scattered the most.
• This blue light reaches our eyes and the sky appeared blue to us.
• In space, due to the absence of the atmosphere, the light rays do not scatter and reach the astronomer's eyes directly therefore the surrounding appears black.

Therefore, 'Absence of atmosphere in space' is the correct response.