MadSci Network: Physics

Re: Why is the sun yellow at noon and red at sunset?

Area: Physics
Posted By: Rob Jeffries, Faculty Astrophysics, Keele University
Date: Mon Jan 20 02:39:20 1997
Message ID: 851822711.Ph

Doug, the first of these is just about right. What happens is 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 of the angle of the Sun. The blue light is scattered away from the line of sight, leaving the red light to go straight through - so the sun looks red. This is also why the sky is blue during the day - scattered sunlight.

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