Earth Sciences and Ecology Question #153

Amy L., a 14 year old female from the Internet asks on March 16, 2000,

What makes the horizon glow pink and red?

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The answer

Barry Shell answered on March 16, 2000

The atmosphere contains lots of atoms which scatter the sunlight in all directions. This is called Rayleigh scattering. It turns out that it is easier to scatter blue light than red. At noon, the sun is overhead and the sunlight does not have to pass through much atmosphere before it reaches us. This leaves the colour relatively unchanged. At sunset though, the sunlight has to travel through a thick layer of atmosphere, because the sun is at a low angle relative to the Earth. The blue light is scattered away from the line of sight, leaving the red light to go straight through - so the sun looks red. The effect of scattered sunlight is also why the sky is blue during the day.

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