How do we know?
↻ One of the pages with a moving picture
Newton spread sunlight into colors with a piece of glass.
- Sunlight looks white, but it is a mix of all the colors of the rainbow.
- When sunlight goes into a raindrop, it bends. Each color bends a different amount, so the colors spread apart.
- The light bounces off the back of the drop and bends again on the way out.
- Millions of drops do this at once. You see a rainbow when the Sun is behind you and rain is in front.
In 1666, Isaac Newton shone sunlight through a glass prism. It spread into a long band of colors. He wrote about it in a famous letter.
A raindrop does the same job as the prism. It bends sunlight and spreads it into colors.
Rainbows need the Sun to be low. On flat ground, the Sun must be lower than about 40 degrees above the horizon for you to see one.
Even the Moon can do it. At Yosemite Falls in California, in April and May, full-moon light on the mist can make a moonbow.
Wow number
40° On flat ground, the Sun must be lower than about 40 degrees above the horizon for you to see a rainbow.
Myth or fact?
A rainbow is really a half circle. Myth. Rainbows are full circles. The ground hides the bottom.
In a double rainbow, the outer bow’s colors are reversed. Fact. Its light bounces twice inside the drops.
Think about it
Why can’t you ever walk to the end of a rainbow?
Where in the world?
Hawaiʻi, USA which one rainbow scientist calls the “Rainbow Capital of the World.” At Yosemite Falls in California, in April and May, full-moon light on the mist can make a moonbow — 21.3069° N, 157.8583° W.
Where these facts come from
Every number on page 31, and who measured it
This page explains how raindrops bend and bounce sunlight, and tells us about full-circle and double rainbows.
Rainbows: optical wonders — The Met Office, the United Kingdom's weather service
weather.metoffice.gov.uk/learn-about/weather/optical-effects/rainbows
We checked it on 31 October 2026
This page tells us how low the Sun must be for a rainbow on flat ground.
Secrets of the best rainbows on Earth — The University of Hawaiʻi
hawaii.edu/news/2021/03/12/best-rainbows-on-earth-hawaii
We checked it on 31 October 2026
This page tells us why Hawaiʻi is called the Rainbow Capital of the World.
Q&A: Expert reveals why Hawaiʻi is World’s Rainbow Capital — The University of Hawaiʻi
hawaii.edu/news/2024/04/02/hawaii-rainbow-capital
We checked it on 31 October 2026
This page tells us about moonbows at Yosemite Falls in April and May.
Lower Yosemite Fall Viewing Area (U.S. National Park Service) — The U.S. National Park Service
nps.gov/places/000/yosemite-falls.htm
We checked it on 31 October 2026
This is Isaac Newton's own letter about his 1666 prism test.
A Letter of Mr. Isaac Newton … containing his New Theory about Light and Colors (Normalized) — The Newton Project at Oxford University, which shares Isaac Newton's own writings
newtonproject.ox.ac.uk/view/texts/normalized/NATP00006
We checked it on 31 October 2026
Has this changed?
How rainbows are made is not going to change.
What does change is where and when you can see one: you need the Sun behind you and rain in front.
Words from this page
- prism
- A piece of glass that bends light and spreads it into colors.
- moonbow
- A rainbow made by moonlight instead of sunlight.
Try it!
Make a rainbow with a glass of water.
1. Fill a clear glass with water. Set it on a sunny windowsill. 2. Put white paper on the floor below, in the light that shines through the glass. 3. Move the paper or the glass until a little rainbow appears.
What happens: the water bends sunlight like a giant raindrop and spreads it into colors.
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