Why Does the Sky Change Color?

-Houston, TX

In the words of Mahatma Gandhi, “When I admire the wonders of a sunset... My soul expands in the worship of the creator.” Sunrises and sunsets are two of the most famously beautiful occurrences in nature. What gives them their vibrant, unique colors?

Pigmentation in the sky can be attributed to a phenomenon called scattering. Scattering occurs when rays of sunlight hit miniscule particles in the atmosphere, changing the direction of light. Blue light is scattered more often than other colors of light because it has a shorter wavelength and thus hits more particles as it travels through the atmosphere. Due to this the sky usually appears blue to our eyes. However, at sunrise or sunset, the sun is low on the horizon and has to travel through more of the atmosphere. Shorter wavelength colors, like blue, are re-scattered so much through the added atmosphere that they are no longer visible. This causes longer wavelengths like red, orange, and yellow to reach our eyes.

Though particles generally give sunsets their vibrant color, not all particles enhance color. Pollutant particles like dust and smoke are generally larger than air molecules but are the same size as light waves, allowing them to absorb light rather than scattering it. When pollutants absorb light, the sky will show pale yellows and pinks as opposed to vibrant reds.

Another factor in the richness of colors during sunset and sunrise is clouds. Clouds also reflect rays of light like air particles, projecting more color during a sunset. Higher altitude clouds like altocumulus and cirrus clouds produce more vibrant color because they reflect rays of light that have not yet been muted by traveling through the atmosphere. On the contrary, lower altitude clouds like stratus and stratocumulus clouds reflect color that has already been muted through scattering thus producing fainter sunrises and sunsets.

Science can explain many of the mystical beauties of nature, including sunrises and sunsets. There is always more to learn, so as always, stay curious!