We’ve all been coming up with rainbows as colorful bridges or arcs extending from one patch of green to another. There is even a so-called “pot of gold” at the end in the folklore. But physics explains the story more symmetrically: there’s no end to a rainbow because it is not an arc at all: It’s a perfect 360-degree circle. That we hardly ever see this full-size ring is less a result of the rainbow and more of how we view things from the ground.
The Geometry of Light : Making the Cone
A rainbow is more of an optical phenomenon than a material thing. It forms when sunlight strikes a raindrop, mirrors back off the drop's back, and refracts (bends) when it returns to the atmosphere. This process occurs at an extremely specific angle – from about 40° to 42° from the “antisolar point”, that point in the sky directly opposite the sun from your point of view.
And since this angle is constant in all directions around that antisolar point, the light getting into your eyes is a cone. When you see the base of the cone from the tip, you are seeing a circle.
The Horizon: The Great Interrupter
If our rainbows were circles, why do we see arcs? The Ground: The bottom half of that light cone when you stand on the Earth’s surface is actually blocked by the ground. There are no raindrops below the horizon line that could be reflected back to your eyes.
The Position of the Sun: As the sun is positioned lower to the horizon, the more of the circle you can see. At sunset, you might see one perfect semicircle (180 °). As the sun rises higher, the arc "sinks" below the horizon until it disappears altogether.
How to See the Full 360° Circle
You have to eliminate the horizon to see complete circle of rainbow. This needs a high position above the water droplets in both directions of your line. Airplanes/Helicopters: Pilots and passengers are the primary witnesses to 360° rainbows. When you soar above a rain shower with the sun behind your aircraft, the shadow of the plane often strikes the center of a perfect, glowing ring of color.
A rainbow is a 360° circle, but only someone at a very high altitude can see the complete circle. pic.twitter.com/V2skEbyhFX
— The Figen (@TheFigen_) February 5, 2026
Skyscrapers and Mountains: Once in a while, if you are sitting top of a very tall building (the Burj Khalifa, for example) or on a steep mountain peak on a misty day, you can spot the lower part of the circle.
The Backyard Hack: You don’t even need a plane ticket to catch a glimpse of a circular rainbow. Stand with your back to the sun and spray small mist around your shadow with a garden hose in a wide circle on a sunny day. When the mist is too thick and your angle is properly adjusted, you will see a little 360° rainbow sprouting directly at your feet!
Rainbow vs. Glory: Don't Get Confused
Frequent fliers often sight a small, rainbow-colored halo centered on the shadow of their airplane on the clouds below. Though beautiful, this is often not a real rainbow but rather a “Glory.” Glories have a much smaller diameter and are obtained from diffraction of light rather than reflecting/refracting light, which causes the entire 40-degree-wide circular rainbow to reflect off of.
