When I was in art school, I looked to my instructors for the answers to all the questions in the artistic universe. Students often question the "facts" presented to them. Because it is my responsibility as an art teacher to give my students the best information possible, I've spent much time over the years researching books and talking to many artists about the "whys" of artistic principles. While many of the questions could be answered easily, some took me years to resolve to my satisfaction. And I have found along the way that many of these "principles" are not based on scientific fact as as much as they are just consistent, tried and true observations made by artists over time.
For example, I was taught that objects appear cooler as they recede into the distance. This is called aerial or atmospheric perspective. Later on I learned that there is one exception to this "rule". Snow gets warmer in the distance.
The science behind this observation I believe is Rayleigh Scattering. This phenomenon occurs when certain particles in the atmosphere scatter a particular wavelength of light.
When the sun is directly above you, the sun's rays travel a relatively short distance through the dense parts of the atmosphere until they reach your eye. According to the Rayleigh model of scattering, blue light is scattered by small particles and gasses in the atmosphere to create the blue sky we perceive. In the distance, Mie scattering of all wavelengths of sunlight by larger dust particles or clouds creates a paler blue in the lower part of the sky. (In the absence of an atmosphere, we would see a black sky}.
At sunset, the sun's rays have much farther to travel through the atmosphere to reach your eye -more than 30 times the distance at midday. This increased distance amplifies the effect of Rayleigh scattering that makes the sky blue, so that the violets and blues in sunlight are lost. The light you see is missing the violets and blues, leaving you with the various shades of yellows, reds, and even purples.
The immense variation in the colors of sunsets depends on the concentration of small particles, or very small aerosols, in the atmosphere. In the absence of these small aerosols, the sky at sunset takes on yellow or orange hues, while increasing concentrations of small particles in the lower atmosphere further increase Rayleigh scattering to shift the hues towards the red end of the spectrum.
Another recent question/observation was posed a few weeks ago in my watercolor class in Kaneville.
Why are colors warmer in the darkest shadows?
When an opaque object is placed in the path of a beam of light, a shadow occurs.
A shadow is the area behind the opaque object where light is blocked.
The darkest part of the shadow is called the umbra.
The umbra is not absolutely dark because scattered light makes its way into the shadow.
The fuzzy part of the shadow is called the penumbra.
The light bends around the edge of the opaque object and scatters the cooler light leaving only the warmer light to penetrate into the umbra.
Understanding how art and science work together can help you create more convincing artwork.