How does the sky appear to an astronaut?  

The correct answer is Dark (Black).

Concept:

Scattering of light

• Scattering of light refers to the process where light rays change direction due to interaction with particles or substances in the medium through which they travel. 
• When light encounters particles that are much smaller than the wavelength of light, it can scatter in various directions.
• Scattering of light plays a significant role in how we perceive the sky's color, the appearance of objects in the atmosphere, and various optical phenomena.

Explanation:

• The sky appears blue when the scattering of light takes place through the atmosphere.
• The blue color of the sky is due to scattering of light from the atmosphere.
• Because there is no atmosphere in space, light does not scatter into its constituent colors, so an astronaut in space sees the sky as dark (black) rather than blue.

Thus, the sky appear to an astronaut is Dark (Black).