Introduction..3 Blue skies...3 Red sunsets.4 Experimentation...5 References7 Blue skies and Red sunsets Throughout history, many people have wondered exactly what makes the sky blue and what makes some sunsets red. This can be done by examinations on how the scattering of sunlight by the Earth's atmosphere produces blue skies and red sunsets. Red sunsets have also been called orange sunsets because they are actually more orange in color. Blue SkiesTo understand why the sky is blue, one needs to understand a little about light. Light is a form of radiation, electromagnetic energy that travels in the form of waves possessing electric and magnetic properties. This form of energy does not need matter to propagate. We can characterize this energy by its wavelength -- the distance along a wave from one crest to another. Our eyes are remote sensors that are sensitive to light with wavelengths between approximately 0.4-0.7 microns (one micron is a millionth of a meter or one one-hundredth the diameter of a human hair). When light interacts with objects that are much smaller than the wavelength of the light, the light being scattered, rather than reflected. The electrons of such a small object are all shaken up and down at the same time by the electric field of the light wave, and they radiate that frequency of light in all directions. It turns out that the higher the frequency of the light, the more the light is scattered. The diameter of most molecules is much smaller than the wavelengths of visible light. A thin protective layer of ozone gas in the upper atmosphere absorbs most of the ultraviolet light from the sun, and the remaining ultraviolet sunlight that passes through the atmosphere is scattered by atmospheric particles and molecules. Of the visible frequencies of light, the high-frequency violet is scattered the most, followed by blue, green, yellow, orange, and red, in the order of decreasing frequency. Red is scattered less th...
