It’s easy to lose yourself in the vivid shades of orange, pink, purple and blue of a Costa Rican sunset. But why do sunsets vary so much from place to place, and from evening to evening? Why are they typically more stunning near beaches, deserts or canyons than in other parts of the world?
To understand the science behind a sunset, you’ll need to remember some basic truths about the nature of light. Light waves come in different wavelengths –some shorter and some longer than others. The sun emits pure unobstructed light, which is white. When it hits the earth’s atmosphere, the atmosphere acts as a prism. Colors with shorter wavelengths scatter (like shades of violet and blue), while colors with longer wavelengths are able to stay more or less on a straight trajectory (like shades of red and orange). This is why the sky appears blue – because blue light scatters very easily as it flies through molecules in the air.
Because the earth is round, the sun becomes farther and farther away as the day wears on. By sunset, it must go through about 10x more space in the atmosphere than it did at noon. This is why at the sunset hour the sky becomes more intense – bluer where it is blue (higher in the sky), and redder where it is red (closer to the sun).
What Makes a Beautiful Sunset?
Air Particles
Atmospheric variables – like pollution, volcanic dust, and even moisture – can have a strong effect on sunsets. Light bounces and scatters off of particles in the air, either absorbing or intensifying how colors to the human eye. Smog tends to absorb and dull the quality of light rather than intensify it, which is why sunsets are usually better in naturally pristine environments than in grungy cities.
Seasons
The time of year also has an effect on how intense a sunset is likely to be. In the Northern Hemisphere, air circulation tends to be slower during the summertime, attracting more fog and smog. This is why sunsets are usually more picturesque during the autumn and winter: the earth is tilted farther away from the sun, so light must pass through more particle-filled space to reach it.
Clouds, Volcanoes and the Tropics
Clouds can also produce vivid pinks, oranges and violets – especially ones that are high enough to intercept “clean” light that has not yet been touched by pollution. Low-hanging clouds can have this same effect in the tropics because the air tends to be cleaner when it’s close to the big blue ocean. While invisible during the day, hazy volcanic particles that linger in the air near volcanoes can have the same effect.
The Green Flash: Blink and You’ll Miss It
That elusive flash of green at the very end of a sunset supposedly does exist – but it takes nearly perfect atmospheric conditions and a seasoned eye to catch it. The moment the “red rubber ball” dips below the horizon line, a green flash sometimes appears at the very tip of the sun for a split second. Stare at the sun before it happens, your eyes won’t be able to see it. Look too late, and it’s gone.
SOURCES
http://www.spc.noaa.gov/publications/corfidi/sunset/
Photo credits: Genna Marie Robustelli of Tamarindo Family Photos
