Stars twinkle, the sky is blue, and the Sun is red at sunset. The air around the Earth is the reason for all three. In this course we study how the atmosphere bends and scatters light, and we use these ideas to explain the colours of the sky.
3 lessons, about 1 h 20 min3 simulations13 problems6 practice questionsPython in every lesson
Created by StemPy LabThe air gets denser toward the ground, so a ray of light from space bends gradually as it comes down. This is atmospheric refraction. It makes stars twinkle, it makes the Sun seem to rise about two minutes early and set about two minutes late, and it makes the Sun look flattened at the horizon.
Scattering is the sending of light in many directions by small particles. In the Tyndall effect, a beam of light through a colloid, a smoke or a dusty room becomes visible, because the particles scatter it. Very small particles scatter mostly blue light, and larger particles scatter longer wavelengths. Very large particles scatter all colours and look white.
The sky is blue because the molecules of the air scatter blue light much more than red light, so scattered blue light comes to the eye from all over the sky. At sunrise and sunset the light travels a long way through the air, most of the blue is scattered out of the beam, and the Sun looks red. Danger signals are red because red light is scattered the least. Without an atmosphere, the sky would be dark.
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