Question

why the sky appear dark to passenger flying at very high altitudes

Answer 1

Do you know why sky looks blue?? please read about that. What do you mean by sky? if you say boundary, then there is none. If by sky you mean the boundary you see, it's color depends on the atmosphere of the planet you are in. For example, in earth it's blue, in Mars it's pinkish/red. If you are in deep space, where there is no atmosphere, it's black. Hope that helps.

Answer 2

Answer:

ya because scattering of light 8s very low there