Why sunsets are colorful

Particles that are small compared with the light wavelength scatter blue light more strongly than red light. Within the visible range of light, red light waves are scattered the least by atmospheric gas molecules.

So at sunrise and sunset, when the sunlight travels a long path through the atmosphere to reach our eyes, the blue light has been mostly removed, leaving mostly red and yellow light remaining. The result is that the sunlight takes on an orange or red cast, which we can see reflected from clouds or other objects as a colorful sunset or sunrise. Large particles of pollution or dust scatter light in a way that changes much less for different colors.

The result is that a dusty or polluted sky is usually more grayish white than blue. Similarly, cloud droplets typically 10 millionths to millionths of a meter are much larger than visible light waves, so they scatter light without much color variation. This is why light scattered by clouds takes on the same color as the incoming light.

For example, clouds will appear white or gray at midday and orange or red at sunrise or sunset. This is why sunsets or sunrises are so much prettier when some clouds are available to show us the colors. If the path is long enough, all of the blue and violet light scatters out of your line of sight. The other colors continue on their way to your eyes. This is why sunsets are often yellow, orange, and red. Tags: curiosities , weather. University of Wisconsin—Madison. Curiosities: What determines the colors of the sky at sunrise and sunset?

Light travels in waves. Every color we see is determined by the length of those waves. Red wavelengths are the longest, and as you go through the rainbow the waves get shorter and shorter until you reach the blues and violets, which are the smallest. But here on Earth, swirling in the air around us are thousands of near-invisible particles. Dust and water droplets are the larger ones, but there are also the minuscule gas molecules—mostly oxygen and nitrogen—that make up the air itself.

Blue wavelengths, because of their smaller size, are scattered more easily and in many directions.