Why does the sky appear dark instead of blue to an astronaut?
The sky appears dark instead of blue to an astronaut because of the lack of atmosphere in outer space. Here's why:

No Atmosphere:
- The Earth's atmosphere scatters sunlight, making the sky appear blue to us on Earth.
- In outer space, where astronauts are, there is no atmosphere to scatter sunlight.
- Without the atmosphere, astronauts see the darkness of space instead of the blue sky.

Blackness of Space:
- In space, there is no atmosphere to scatter sunlight in all directions, so the sky looks dark.
- Astronauts see the vastness of space filled with stars, planets, and galaxies, which creates the dark sky effect.

Lack of Sunlight Scattering:
- On Earth, sunlight enters the atmosphere and scatters in all directions, making the sky appear blue.
- Without the atmosphere in space, there is no scattering of sunlight, leading to a dark sky.

Conclusion:
- The absence of an atmosphere in outer space causes the sky to appear dark instead of blue to astronauts.
- This unique perspective allows astronauts to experience the beauty and vastness of space firsthand, with a backdrop of darkness rather than a blue sky.