Supernumerary Rainbows

Last updated on September 16, 2023

Supernumerary Rainbows: A Delightful Phenomenon in the Sky

Rainbows have long captivated our imagination with their vibrant colors and ethereal beauty. But did you know that there is more to rainbows than meets the eye? Enter supernumerary rainbows, a fascinating atmospheric optical phenomenon that adds an extra touch of magic to the already enchanting display.

What are Supernumerary Rainbows?

Supernumerary rainbows are faint, closely spaced bands of colors that appear just inside the primary or secondary rainbow. They are often seen as a series of pastel-colored fringes, resembling miniature rainbows within the larger bow. Unlike the main rainbow, which displays a continuous spectrum of colors, supernumeraries exhibit discrete bands that alternate between light and dark hues.

The Science Behind Supernumerary Rainbows

To understand the formation of supernumerary rainbows, we need to delve into the intricate behavior of light as it interacts with water droplets in the atmosphere. When sunlight passes through these tiny droplets, it undergoes a process called diffraction. This phenomenon causes the light waves to bend and interfere with each other, resulting in the formation of the supernumerary bands.

The key to the appearance of supernumeraries lies in the size of the water droplets. For these secondary rainbows to occur, the droplets must be extremely uniform in size, with diameters on the order of micrometers. It is this uniformity that allows the diffracted light waves to reinforce or cancel each other out, creating the distinctive pattern of bright and dark bands.

Where to Spot Supernumerary Rainbows

Supernumeraries can be observed in various settings where water droplets are present, such as after a rainfall or when mist hangs in the air. However, one of the best places to witness these elusive phenomena is through garden hosepipe sprays. The droplets produced by hosepipe sprays tend to have similar diameters, making them ideal for the formation of clear and distinct supernumeraries.

Captivating Examples of Supernumerary Rainbows

Photographers and sky enthusiasts have managed to capture the elusive beauty of supernumerary rainbows in stunning images. One such example is a photograph taken by Michael Ellestad, showcasing a hosepipe spray rainbow with a faint supernumerary visible to the naked eye. The image highlights the delicate nature of the supernumeraries, which often appear as subtle enhancements to the primary or secondary bow.

Another captivating image, captured by Les Cowley, features a secondary supernumerary that is just visible after enhancing the contrast. While the primary colors may be distorted in the process, the faint supernumerary still manages to leave its mark on the scene. These photographs serve as a testament to the allure of supernumerary rainbows and the skill required to capture their ephemeral beauty.

Exploring the Wonders of Atmospheric Optics

Supernumerary rainbows are just one example of the countless atmospheric optical phenomena that grace our skies. From halos and sundogs to iridescent clouds and glory, the study of these mesmerizing displays offers a window into the intricate workings of light and atmospheric conditions. By understanding the science behind these phenomena, we gain a deeper appreciation for the natural wonders that surround us.

Conclusion

Supernumerary rainbows are a delightful addition to the already captivating display of rainbows. These faint bands of colors, closely spaced within the primary or secondary bow, offer a glimpse into the complex interplay between light and water droplets in the atmosphere. Whether observed through garden hosepipe sprays or captured in breathtaking photographs, supernumerary rainbows remind us of the beauty and mystery that abound in our natural world. So, next time you find yourself gazing at a rainbow, take a moment to search for these enchanting celestial companions and let them transport you to a world of wonder.

Secondary rainbows have very faint and broad supernumeraries outside the main bow.

Rainbows from garden hosepipe sprays often show them. In the image look to the left and below the blue of the secondary bow to see its faint supernumerary.

Hosepipe sprays produce clear supernumeraries because their droplets have very similar diameters.

Michael Ellestad (site) made this hosepipe bow. Image ©Michael Ellestad.

A secondary supernumerary is just visible in this much enhanced image. The primary's colours are grossly distorted by the contrast increase.

The two bows were not particularly bright but the supernumerary was faintly visible to the unaided eye.

Photo: Les Cowley

Another secondary supernumerary.

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Reference Atmospheric Optics

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