Extras

Last updated on September 16, 2023

Extras: Exploring the Phenomenon of Supernumerary Rainbows

When we think of rainbows, we typically envision a beautiful arc of colors stretching across the sky. However, there is more to this optical phenomenon than meets the eye. In addition to the primary rainbow, there are "extras" known as supernumerary rainbows that add an extra touch of magic to the atmospheric display. These colored fringes inside the primary rainbow were once considered inexplicable, defying the principles of geometric and Newtonian optics. But with a deeper understanding of the wave nature of light, we can now unravel the mystery behind these mesmerizing extras.

The Wave Nature of Light

To comprehend the formation of supernumerary rainbows, we must first grasp the concept of light as waves rather than classical rays. When light passes through a raindrop, it can take two distinct paths and still emerge at the same angle to contribute to the creation of a rainbow. By replacing the traditional rays with waves, we gain insight into how supernumeraries come into existence. Imagine two sets of wave crests emerging from the raindrop but out of step with each other. At certain angles, these waves cancel each other out, resulting in no visible light. However, as the angle of emergence changes, the waves alternate between being in step and out of step, leading to the formation of light and dark interference fringes known as supernumeraries.

The Colorful Array of Supernumeraries

Upon closer examination, we discover that supernumerary rainbows exhibit predominantly green and purple hues. This color diversity stems from the fact that waves of different frequencies (or colors) have distinct fringe spacings. These overlapping waves create a complex interplay of colors, resulting in the vibrant palette observed in supernumeraries. The intricate patterns and shades serve as a testament to the intricate nature of light and its interaction with water droplets in the atmosphere.

The Mystery of the Bow Top

One intriguing aspect of supernumerary rainbows is their tendency to appear primarily near the top of the primary rainbow. The reasons behind this phenomenon are still being explored and studied by scientists. While no definitive explanation has been established, several factors may contribute to this concentration of supernumeraries near the bow top. These factors could include variations in droplet size and shape, as well as the specific angles at which light enters and exits the droplets. Further research is needed to fully unravel this enigma and shed light on the precise mechanisms at play.

Embracing the Magic of Nature

The existence of supernumerary rainbows serves as a reminder of the intricate beauty and complexity of the natural world. As we delve deeper into the wave nature of light and its interaction with water droplets, we uncover hidden wonders that enhance our understanding of atmospheric optics. Supernumeraries are a testament to the harmonious interplay between physics and nature, showcasing the delicate balance of scientific principles and artistic allure.

Capturing the Elusive Extras

Photographers and enthusiasts alike strive to capture the elusive beauty of supernumerary rainbows. These intricate features of atmospheric optics provide a unique challenge for those seeking to document their existence. By utilizing specialized equipment and techniques, photographers can showcase the vibrant colors and ethereal patterns of supernumeraries, allowing us to witness their enchantment even when they momentarily grace our skies.

A Glimpse into Atmospheric Optics

The study of atmospheric optics is a fascinating field that encompasses various phenomena, including rainbows, halos, and mirages. Each of these optical marvels offers a glimpse into the intricate workings of light as it interacts with particles in the atmosphere. By delving into the details of these phenomena, scientists gain valuable insights into the fundamental properties of light and its behavior in different atmospheric conditions.

Exploring Beyond Rainbows

While rainbows and supernumeraries are undoubtedly captivating, there is a wealth of other atmospheric optical phenomena waiting to be explored. From the intricate ice crystal displays of halos to the mesmerizing mirages that distort our perception of reality, the atmospheric realm offers a cornucopia of visual wonders. By venturing beyond rainbows, we can uncover a multitude of optical delights that continue to captivate and inspire scientists and nature enthusiasts alike.

Appreciating the Dance of Light and Water

As we marvel at the spectacle of supernumerary rainbows and other atmospheric optical phenomena, let us take a moment to appreciate the delicate dance between light and water. These enchanting displays serve as a reminder of the intricate interplay between the laws of physics and the beauty of nature. By embracing and studying these phenomena, we deepen our understanding of the world around us and develop a greater appreciation for the wonders that unfold above us in the ever-changing tapestry of the sky.

A Window into the Sublime

Supernumerary rainbows are not just extras; they are windows into the sublime beauty and complexity of the natural world. Through these colorful fringes, we catch a glimpse of the hidden intricacies that lie within raindrops and light waves. By unraveling the secrets of supernumeraries, scientists continue to push the boundaries of our knowledge and deepen our connection with the awe-inspiring phenomena that grace our atmosphere. So, the next time you find yourself gazing at a rainbow, remember to look beyond the arc and embrace the extras that add an extra touch of wonder to our world.

Rainbow with Supernumeraries imaged by Eva Seidenfaden (Paraselene Optics Site) at Trier, Germany on June 27th '08. ©Eva Seidenfaden, shown with permission.

Supernumeraries, coloured fringes inside a primary rainbow were supposed not to exist. They could not be explained by geometric or Newtonian optics. They are a consequence of the wave nature of light.

Light can take two paths (top left) through a raindrop and yet emerge deflected through the same angle to contribute to a rainbow. Replace the classical rays by waves (right drop) and we can see how supernumeraries form. In the example, the emerging two sets of wave crests are out of step and no light would be seen at that angle. As the emergence angle changes the waves alternate between being in step and out of step. The result, the light and dark interference fringes we call supernumeraries.

As Eva's close-up shows, the supernumeraies are predominantly green and purple hued. Waves of different frequency (colour) have different fringe spacings and overlap to form the complex hues. Why do supernumeraries appear mostly near the bow top? That is another story.

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Reference Atmospheric Optics

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