Why are sunsets red and orange?
Sunsets look red and orange because sunlight travels through much more air when the Sun is low. Air scatters away most of the blue light, leaving the warm colors.
Sunlight contains all colors. As it passes through the atmosphere, tiny gas molecules scatter short wavelengths, like blue and violet, much more than long ones, like red and orange. This effect, called Rayleigh scattering, is also why the daytime sky looks blue.
When the Sun is near the horizon, its light has to cross many times more atmosphere to reach you than at noon. By the time it arrives, most of the blue has been scattered out of the direct beam. What remains is mostly red, orange and yellow light, which colors the Sun and the clouds around it.
What makes some sunsets spectacular
Dust, smoke and volcanic ash can make sunsets deeper and more colorful. After large volcanic eruptions, such as Krakatoa in 1883 and Pinatubo in 1991, people around the world saw unusually vivid sunsets for months. Clouds high in the sky also catch the light and glow after the Sun has set.
Did You Know?
On Mars the colors are reversed. Fine dust in the Martian air makes the daytime sky look reddish, while sunsets there appear bluish around the Sun.