Astronauts on a space station, far above most of the air, see a black sky even in full sunlight…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Astronauts on a space station, far above most of the air, see a black sky even in full sunlight. Yet the Earth below them looks blue. Explain both.
Need a reminder? The key ideaShow
The sky is blue because air scatters blue toward us from every direction. Near the horizon sunlight crosses much more air, about times as much for a Sun degrees high, so most of the blue is scattered away and the Sun looks red.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The black sky. Around the station there is almost no air to scatter sunlight toward the astronauts' eyes, so the sky is black and the stars show.
Step 2. The blue Earth. The Earth's air lies below them. It scatters blue sunlight in all directions, some of it upward, so the Earth looks wrapped in blue.
Answer: no air around them to scatter light; plenty of air below, scattering blue.
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