The science of rainbows
Welcome! I'm excited to explore the science behind one of nature's most beautiful displays with you.
To help me tailor this session, what is your current understanding of rainbows or basic physics, and what sparks your interest in this topic?
I'm a beginner! I just know they happen when it rains and shines at the same time.
Your path
The Physics of Light
Inside the Droplet: Refraction, Reflection, Dispersion
Advanced Rainbow Concepts
The Perfect Recipe for a Rainbow
You are actually spot on! Having both rain and shine simultaneously is the absolute core of how a rainbow appears, but there is one more essential ingredient: you.
To see a rainbow, you must stand with the and the water droplets directly in front of you. Because of how light bounces, the center of every rainbow is physically aligned with your own shadow.
What is a rainbow?
To understand what a rainbow is, we have to start with a surprising truth about sunlight: the clean, bright light we see every day is actually a mixture of every color in the universe combined.
Scientists call this , and it contains all the colors of the visible spectrum: red, orange, yellow, green, blue, indigo, and violet. Normally, these colors travel together so closely that they blend into one single, colorless beam. To see them, we have to find a way to separate them.
Continue to how different wavelengths make these colors
To understand how white light splits into its vibrant colors, we have to look at light as a series of traveling waves.
Just like waves in the ocean, light waves have —the physical distance from the crest of one wave to the crest of the next. Red light has a longer wavelength, while violet light has a much shorter, tightly packed wavelength.
Comparison of two light waves showing a red wave with long wavelength (λ1 = 700 nm) and a blue wave with compressed wavelength (λ2 = 400 nm).
Now, here is the secret to the separation: when light enters a water droplet, it slows down because water is denser than air.
Because of their physical size, different wavelengths don't slow down equally. The short, energetic violet waves get slowed down and bent—or —the most, while the long red waves plow through with less bending. This unequal bending is what stretches the single beam of white light out into the orderly spectrum of colors we see in the sky.