When viewed from an airplane, the shape of a rainbow appears as a full circle.
While observers on the ground typically see a rainbow as a semi-circle, gaining altitude in an aircraft offers a unique perspective that allows the full circular arc to become visible. This phenomenon is directly related to how rainbows are formed and our vantage point.
The Science Behind Circular Rainbows
Rainbows are atmospheric optical phenomena that occur when sunlight interacts with water droplets suspended in the air. Specifically:
- Light Refraction: As sunlight enters a water droplet, it bends (refracts).
- Internal Reflection: The light then reflects off the back of the droplet.
- Second Refraction: It refracts again as it exits the droplet, scattering into its constituent colors.
The specific angle at which this light emerges and enters our eyes determines what we perceive as a rainbow. Rainbows are not physical objects located at a certain distance but rather optical illusions whose apparent position depends on the viewer's angle relative to the sun and the water droplets.
Why the Difference Between Ground and Air View?
The key distinction lies in the viewer's perspective and the horizon line:
- On the Ground: From the ground, the horizon obstructs the lower half of the rainbow's full circular shape. We only see the arc above the horizon, which appears as a semi-circle. The ground itself blocks the view of the lower part of the circle.
- From an Airplane: When you are high in an airplane, your vantage point is above much of the ground-level obstruction. This allows you to look down and see the light reflecting from water droplets that are below the traditional ground horizon, completing the circle. You are essentially viewing the entire cone of light that creates the rainbow.
Key Takeaway: The circular nature of a rainbow is always present, but our ability to perceive its full form depends entirely on our elevation and line of sight relative to the water droplets and the sun. From an airplane, with fewer obstructions, the complete, beautiful circular shape becomes apparent.
