When it rains, sometimes we can see oil on the street rise to the top of puddles and spread out into a rainbow of colors.

Cigdem Capan.

One of the main reasons we see color is because of light, said my friend Cigdem Capan, a physics instructor at Washington State University.

She reminded me that when our eyes sense colors, we can trace those colors back to different wavelengths of light. Perhaps you can make some waves in the air with your hand. Make small, tight waves. Now make a big, wide waves.

The light waves that help us see color are a lot smaller than any wave we can make with our hand. According to our friends at the National Oceanic and Atmospheric Administration, blue or violet wavelength is about 125 times smaller than the width of a human hair.

The colors that you see in an oily puddle are also a kind of phenomenon we call iridescence. We can see this phenomenon when we observe the outside of soap bubbles or the colorful feathers of the male peacock.

Find out more

Ask Dr. Universe