6 Bows

6 Rainbows - Captured by Nola Davies looking over Camden Haven River approx 350 km north of Sydney, Australia. ©Nola Davies, shown with permission.

This tranquil early morning scene contains at least six rainbows.

The bright primary with its supernumeraries and secondary with inverted colours are obvious.

Between them is a faint 'reflection bow'. (Rainbow nomenclature with its 'reflection and reflected bows is not easy!)

Three more bows appear below the horizon in front of the water.

Reflection primary

Sunlight reflected off the water and traveling upwards makes the reflection bow. To raindrops, the reflected light appears to come from a second sun the same angular distance below the water as the real sun is above it.

The 'second sun' forms a rainbow centered on a point opposite in the sky called the 'anthelic point'. The reflection bow intersects the ordinary primary at the horizon and curves above it in the sky.

Secondary bows also produce reflection rainbows and there is a trace of one in the image between the two yachts and the red buoy.

Bows in front of the water

The bows below the horizon are not reflections in the true sense. Rainbows do not exist as real objects and therefore do not have reflections. The bows beneath the horizon are formed by different raindrops from the ones that formed the sky bows. They are called reflected bows.

Reflected bows are made by rays that are reflected by the water surface after they have passed through raindrops. The reflection inverts the rainbow and the bow centre is then above the horizon at the anthelic point. The reflected bow and the corresponding ordinary bow meet in a cusp at the horizon.

The reflected - reflection primary bow below the horizon is formed by a tortuous ray path. Sunlight reflects off the water and travels upwards. It then meets raindrops which form rainbow rays. These reflect again off the water into the eye.

The continuation of the primary follows the same path and the two bows are superimposed. The intensity of the reflected bow and the extent to which the suspected 'reflected-reflection' bow's intensity falls off with distance from the horizon give some clues as to its contribution relative to a pure continuation of the primary. A rapid fall off for an observer close to the ground or sea surface suggests a primary bow continuation. Here there is probably a contribution from both bows.