Yes, a rainbow is actually a full circle. We typically only see a partial arc because the Earth's surface blocks the lower portion of the circle.
Why We Only See an Arc
- The curvature of the Earth obscures the lower half of the rainbow's circular shape when viewed from the ground. We only see the portion of the circle above the horizon.
- The necessary conditions for observing a complete circular rainbow, such as the presence of water droplets both above and below the horizon, are rare at ground level.
Seeing the Full Circle
To see a complete circular rainbow, you need to be in a position where the entire circle is visible above the horizon. This is possible:
- From a high vantage point: Airplanes, tall mountains, or even tall buildings can offer a perspective that allows you to see the entire circle.
- With the right atmospheric conditions: Sufficient water droplets in the air, at various altitudes, are essential. This isn't always the case, even from high altitudes.
Multiple sources confirm that rainbows are indeed full circles, and the perceived arc is solely due to our viewing perspective and the Earth's curvature. As noted in several articles (National Geographic, Big Think, EarthSky, and many others), observing a complete circular rainbow is possible, but requires the right circumstances.
