The science of rainbows
Welcome! I'm so excited to explore the beautiful science behind rainbows with you. Before we dive into how these stunning bands of color form, I'd love to know a bit about where we are starting from.
To help me tailor this session perfectly to you, what is your current understanding of light and optics, and is there any specific part of rainbow science you're most curious about?
I am totally new to optics and want to start from the absolute basics!
Your path
The Physics of Light
Rainbow Characteristics and Variations
An Optical Illusion of Light
Let's start at the absolute beginning: a rainbow isn't a physical object. It's not a colorful ribbon hanging in the sky, and you can't hike over to touch it or find that legendary pot of gold at its end. Instead, a rainbow is an , which is just a scientific way of saying it's a beautiful trick of the eye. It only exists as an image formed by light hitting your eyes at a very specific angle. If you move, the rainbow moves with you!
Because it's an illusion of light rather than a physical structure, every single person actually sees their own unique rainbow. The droplets reflecting light to your eyes are different from the ones reflecting light to the person standing right next to you!
Let's continue to the three essential ingredients.
Now let's talk about the master key that unlocks how a rainbow positions itself in the sky: the . Even though it sounds like something out of science fiction, it's actually just a fancy geometric term for the imaginary spot in the sky that is directly opposite the Sun from your point of view.
Think of it as a straight line running from the Sun, straight through the back of your head, out through your eyes, and pointing directly ahead of you. If you were standing outside on a sunny day, the head of your shadow on the ground would mark this exact spot.
Every rainbow is actually a perfect circle centered around this imaginary point! Because the ground blocks the bottom half of the circle, you usually only see the top half as a colorful arc.
A 2D perspective diagram illustrating the geometric line from the Sun behind an observer, through the observer's head, to the antisolar point below the horizon, with the visible top arc of the rainbow cone.
Since the rainbow is centered on the antisolar point, and that point is directly opposite the Sun, the height of a rainbow changes depending on where the Sun is in the sky. If the Sun is high, the antisolar point is pushed deep underground, hiding most of the rainbow. But if the Sun is low, near the horizon, the antisolar point rises, and you get a stunning, tall arch in the sky!