Rainbows can sometimes form a complete circle from an airplane because the height at which the observer is situated influences the perception of the rainbow. From an airplane, with a bird's-eye view of the water droplets, the rainbow may appear to form a complete circle.
When you're on a plane, you are at an altitude much higher than on the ground. And that changes everything when it comes to seeing a full-circle rainbow. From the air, nothing blocks the light, unlike on the ground where the earth cuts off the view. Essentially, the height gives us a clear view of the entire rainbow. The higher up you are, the more the viewing angle allows you to see the complete circle. The plane offers an unobstructed view, making it possible to admire this spectacular effect that you never see from solid ground.
Rainbows appear when the sun is low in the sky. In flight, this rule changes a little. When you are in the air, the sun can be at different angles relative to you. To see a full-circle rainbow, the sun must be behind the plane. The plane acts like a sort of screen, and you see the rainbow in front of you. The circle forms because the light is scattered in all directions, not just in an arc. It's a bit like being at the center of a circle of colors. The higher the plane, the clearer the view of the circle.
Rainbows are formed through two key phenomena: refraction and reflection of light. When sunlight hits a water droplet, it bends upon entering — this is refraction. Then, inside the droplet, the light reflects off the inner wall and bends again as it exits the droplet. This double bending separates the colors of the light into a true prism-like display. The white light from the sun is composed of all the colors of the rainbow. Each color bends differently, resulting in a range of distinct colors. That’s why rainbows are so colorful.
To see a full circle rainbow, you need water droplets suspended in the air, essentially clouds or rain. The smaller and more numerous these droplets are, the better it is for the formation of the rainbow. Sunlight enters these droplets, gets reflected inside, and exits, splitting into different colors. When you're in an airplane, you're above the cloud layer, so you can see the arc from above, where it appears as a full circle. Humidity and air purity are also important. Very polluted or dry air will hinder the formation. That's why it's easier to see the complete arc from a plane than from the ground.
Full circle rainbows seen from an airplane are related to the halo effect and the dispersion of light. When sunlight enters a raindrop, it is refracted, then reflected inside the drop, and finally exits by refracting again. This process separates the light into its different colors. Normally, from the ground, we only see a half-circle. But from an airplane at the right angle, the light follows the same path in each visible drop both above and below the plane, forming a full circle. It's a bit magical, but it's just physics at work.
The phenomenon of rainbows has been widely studied for centuries, and the first scientific explanations date back to the time of Aristotle in ancient Greece.
In reality, there are double rainbows, where a second, fainter and wider rainbow can be observed outside of the first rainbow.
Rainbows are not only observable from Earth, they can also form on other planets in the solar system, such as on Mars for example.
A rainbow is an optical and meteorological phenomenon resulting from the dispersion of sunlight by water droplets in the atmosphere.
The colors of a rainbow are due to the dispersion of white sunlight by water droplets, which separate light into different wavelengths.
A rainbow is usually in the shape of a half-circle, visible from the ground at a certain angle relative to the sun.
A circular rainbow can form when the observer is at a high altitude, such as from an airplane, allowing them to see the rainbow in its entirety.
The main difference is that the circular rainbow can be observed in its entirety, forming a complete circle, while the traditional rainbow is usually a half-circle.
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