More than captivating colors: the science behind sun rises and sunsets


Flannery Enneking-Norton

The bold colors of the setting sun are caused by the interaction of light waves with air and pollutant particles. Clear winter air increases the colors’ brightness, which is why the recent dawns and dusks have been particularly radiant.

Fiery orange radiates from the slowly rising orb, as pinks and purples paint the soft and glowing sky. The past few weeks have had many notably inspiring sunrises and sunsets, with many people taking to Instagram and Snapchat to record the beauty.

Everyday phenomena like sunrises and sunsets are easy to take for granted, but understanding the science behind these events adds to the experience. The normal warm hues of sunrises or sunsets are due to the way air particles interact with light waves. The sun emits a spectrum of light waves ranging in sizes. Colder colors, like blue, are smaller and closer in size to air particles, which means the air particles reflect or scatter that color more effectively. At sunrise or sunset, the light travels at a shallower angle and a greater distance through the sky, which means most of the blue has been scattered out, leaving the reds and oranges associated with the rising or setting sun behind to light up the sky.

The bold palette of colors displayed in the sky as of late can be attributed in part to the changing seasons. Air circulation is slower in the summer and the density of smog is greater, which dims the brilliance of the colors. The crisp, clean autumn and winter air means there is maximum scattering possible, resulting in the heightened beauty of the sun.

Despite the pristine and magnificent look, the increased redness at sunrise and sunset also has a tainted origin: air pollution. Although smog and cloud cover diminishes the strength of the light’s hues, research suggests some pollutant particles also contribute to increased redness, giving weight to the claim that more brilliant sunsets is indicative of climate change. Generally, dust particles and other pollutants soften the sun’s colors because they are larger, and scatter more of the light before it reaches the ground resulting in a less vibrant sky. However, aerosol particles are closer in range to the size of red light wavelengths, so in areas with higher air pollution the redness at sunset is accentuated. Furthermore, pollutant particles of different sizes can come together and scatter different colors more effectively, increasing the brightness of the sky–although the colors themselves remain dimmed. The glowing sky is partially due to the smaller dust or air particles that are higher up and are only illuminated by sunlight after the sun has reached the horizon (due to the greater angle that the light is emitted).

Although increasing air pollutants pose both health and environmental concerns, sunset admirers need not feel guilty for appreciating the sun’s beauty. The extraordinary brilliance of it this time of year is primarily due to the changing seasons, and not climate change. The best time to catch the painted sky is in the late afternoon, or right before school begins. While winter does bring that bitter cold, the brilliant sky brightens up any freezing day, and makes the season worth it.