Question

why does sky appear red during sunriseand sunset?

Answer 1

During sunrise and sunset, the rays have to travel a larger part of the atmosphere because they are very close to the horizon. Therefore, light other than red is mostly scattered away. Most of the red light, which is the least scattered, enters our eyes. Hence, the sun and the sky appear red.

Answer 2

this is due to the phenomena of scattering of light. As red light scatters the least it can travel long distance so during sunrise and sunset. other lights may fade due to passing from the layers of atmosphere as they have shorter wavelength.