Earth's Color Carousel

(calming music) Today's episode is all about the way that our experience of color changes over the course of a day, a natural phenomenon we don't even notice. The vibrant range of visible light we see from sunrise to sunset obviously brightens, then darkens. But this evolution also turns through every color on the color wheel. It's a good reminder of how our lives continue to change, never staying exactly the same from one moment to the next. When the morning sun begins to rise in the east, its reddish-orange glow illuminates the world. This light heightens the chroma or intensity of orange and red objects, but dulls blue-green ones, making red barns radiate and spruce trees dull to olive. These optical phenomenon are explained by the physical properties of our environment. Our atmosphere, full of nitrogen and oxygen, scatters the shorter wavelengths of white light coming from the sun, making the sky appear blue, and diffusing the longer wavelengths of red, orange, and yellow. As the sun begins to climb and brighten the sky, its red-orange light becomes more clearly orange, and then morphs into the dominant yellow that we think of when we think of sunlight. Curiously though, the light that illuminates buildings, woods, lakes, and meadows is actually a composite of that yellow sun, and a huge source of reflected blue from the dome of the sky. And so what we see resembles a green light source, enhancing the green hue of foliage and anything else that's green. It's an effect that reaches its peak at high noon, and then reverses over the afternoon hours, until we land again at the orange-red of sunset and its long, cool, blue shadows. During the evening hours, we have the dark blue-violet starlit sky, and a moon of pale white reflected light that looks greenish-blue to us, reducing shadows with dark cranberry tones, blue-green's color complement, or opposite on the color wheel. When the stars and moonlight slowly disappear as the moon sets and the morning sun rises again, we begin another turn on a ride as old as the Earth itself, the color carousel. (calming music)...