Without atmosphere, what would the sky look like from the surface?

• A. The sky would appear blue.
• B. The sky would appear red.
• C. The sky would appear green.
• D. The sky would appear black.

Answer: (D)

The sky’s color comes from how sunlight interacts with the air. When sunlight hits the atmosphere, gas molecules scatter shorter blue wavelengths in all directions, so the sky looks blue during the day. Without an atmosphere, there’s nothing to scatter the light. Light would travel in straight lines, and the vast majority of the sky would look like black space, with only the Sun as a very bright focal point. So from the surface, the sky would appear black. (If you look away from the Sun, you could also see stars, since there’s no atmospheric glow to wash them out.)