Why are the colors of the rainbow visible at sunset?


Why are the colors of the rainbow visible at sunset?

In: Physics

The rainbow is light refraction through a medium which changes the speed of light.

What you have to understand is that white light is composed of many wavelengths and depending on the wavelength its a different color.

Now comes the idea of refraction, which is that in a medium that changes the speed of light, different wavelengths with different frequencies will be slowed down at different rates, so the light fans out to different color… thats how a rainbow works.

Now… why can you still see it in sunset, because there is still some light.

Funny enough, this is very closely related to the question “why is the sky blue?” (If I’m understanding your question correctly.) When light comes into our atmosphere, it bounces off of the molecules of air. However, some wavelengths (colors) bounce off better than others. In particular, blues and violets bounce off of the molecules much better than, say reds and oranges. What this does is spread the blues and violets out over the sky so it looks like those colors are coming from all around rather than just directly from the sun. That’s why the sky looks blue. However, the more that a color scatters in the atmosphere, the less of it there is deeper in the atmosphere. When the sun is setting, the light is traveling much farther through atmosphere to reach you than when the sun is overhead. The blue light scatters off and spreads out very quickly, leaving only the reds, oranges, and yellows (and sometimes greens as well). As my old professor put it, sunsets are pretty because all of those bastards to the west are stealing all the blue!