Why isn't the sky violet instead of blue?

This is an excellent question. Based on Rayleigh scattering, violet light has an even shorter wavelength than blue light, so it is scattered even more powerfully. Logically, the sky should look violet. However, the sky appears blue to us due to a combination of two main factors: how the Sun works and how our eyes work.

• 1. The Sun's Output: The Sun does not emit all colors of light equally. It emits slightly less violet light than it does blue light. So, even though violet is scattered more strongly, there is simply less of it to begin with.
• 2. Human Eye Sensitivity: This is the biggest reason. Our eyes are not equally sensitive to all colors. The light-detecting "cone" cells in our retinas are most sensitive to red, green, and blue light. While our blue-sensitive cones are strongly stimulated by the blue light, our violet-sensitive cones are less responsive.

When our brain takes in all the signals—the large amount of scattered blue light (which our "blue" cones are very sensitive to) and the slightly larger amount of scattered violet light (which our "blue" cones *and* "red" cones perceive slightly, but our "violet" sensitivity is weak)—it mixes them together and interprets the final color as the familiar shade of "sky blue."