Complete double rainbow encircles Australian town

A full double rainbow, captured from a helicopter flying over Cottesloe Beach in Western Australia, frames a golf course near Perth. A downpour reflects light from the setting sun back toward photographer Colin Leonhardt, creating two concentric rings of color that appear to encircle the course.

You can’t touch a rainbow; birds can’t fly over them, and leprechauns can’t loiter at their ends. A rainbow is an illusion crafted by mist. Each water droplet behaves like a prism suspended in the air. The colors embedded in sunlight separate as they race through the droplet at different speeds. When the bands of color reach the far end of the drop, they bounce back toward the sun. People looking toward the mist with their back to the sun can see the rainbow.

All rainbows are round, but seeing a full circle requires a viewing area with plenty of droplets in all directions; that’s tough for people on the ground. When the observer flies through a water-laden sky, however, a complete rainbow emerges.

The second, dimmer rainbow appears when light bounces off the inside of raindrops twice before coming back. Because most of the light leaks out after just one reflection, secondary rainbows are usually much fainter than primary ones.