Samos Supernumerary Rainbows - OPOD

Samos Supernumerary Rainbows - OPOD: A Detailed Exploration

Rainbows have long captivated our imaginations with their vibrant colors and ethereal beauty. But did you know that rainbows can exhibit additional bows within their arcs? These fascinating optical phenomena, known as supernumerary rainbows, can be observed arching over the Greek island of Samos. In this article, we will delve into the intricacies of Samos supernumerary rainbows, shedding light on their formation and characteristics.

The Primary and Secondary Rainbows

When the sun is low in the sky, primary and secondary rainbows grace the horizon above Samos. The primary rainbow is the innermost arc, while the secondary rainbow appears as a fainter and broader outer arc. Both rainbows are adorned with a fringe of supernumerary bows, creating a mesmerizing spectacle for those fortunate enough to witness it.

Alexander's Dark Band

Between the primary and secondary rainbows lies a peculiar phenomenon known as Alexander's Dark Band. Although there are an equal number of raindrops in this region as elsewhere, they do not glint light towards us. This absence of glinting light creates a dark band, contrasting with the vibrant colors of the surrounding rainbows.

The Formation of Supernumeraries

Supernumeraries owe their existence to the interaction of light with raindrops. As rays of sunlight pass through raindrops, they undergo reflection and refraction. The primary rainbow emerges from rays that are reflected once inside the raindrops. These rays converge at the rainbow's rim, producing the familiar colors we associate with rainbows.

The Play of Light and Color

Within the rainbow's rim, rays passing closer to the drop center deflect and illuminate the sky. Each ray exhibits bright colors, but when combined with the millions of drops present, these colors mix to create white light. It is at this point that waves of light overlap, resulting in a series of bright fringes known as supernumeraries. The angle at which these fringes appear depends on the color of the light, giving rise to a stunning display dominated by greens and purples.

Observing Secondary Supernumeraries

While supernumeraries within the primary rainbow are relatively common, spotting secondary supernumeraries is a rare occurrence. These faint, broad bows with low contrast require specific conditions for visibility. A dark background sky and fine raindrops of similar sizes aid in their observation. When enhanced, secondary supernumeraries become more apparent, showcasing their broader and more widely spaced nature compared to those within the primary.

The Crowding Effect

As one's gaze extends towards the center of the rainbow, the supernumeraries gradually fade and become increasingly crowded together. This phenomenon occurs due to the nature of wave interference. The overlap of wave crests creates areas of bright light, while areas where crests cancel out result in darkness. The spacing and intensity of the supernumeraries vary with angle, culminating in a beautiful convergence towards the center of the rainbow.

Samos supernumerary rainbows offer a captivating glimpse into the intricate interplay between light and water droplets in our atmosphere. They remind us of the vast complexity that lies within seemingly simple natural phenomena. So, the next time you find yourself on the enchanting island of Samos, keep your eyes peeled for these extraordinary optical wonders that grace its skies.

Samos Supernumeraries ~ Primary and secondary rainbows arch over the Greek island of Samos. Both are fringed by supernumerary bows, . Images by Manolis Thravalos (more images). Images ©Manolis Thravalos, shown with permission

These bows have all. Almost semicircles from the low sun. Nearby glinting raindrops extend the primary beneath the horizon. The sky whitens inside the primary and the nearby Turkish coast blots out.

The same number of raindrops are there as elsewhere but they glint light, rainbow light, to the eye and camera. Between the bows the drops glint no light towards us (yet they glint elsewhere) – Alexander’s Dark Band. The sky lightens again outside the secondary from more rainbow light. Rainbows are not rings.

The inner primary and outer secondary light creates supernumeraries. Those inside primaries are common.

Secondary supernumeraries - seen at 2 o’clock on the top image and enhanced at right – are rare. They are faint. They are broad. They have low contrast. A dark background sky helps visibility. So does fine rain whose drops are nearly the same size.

Right: Levels enhanced crop from the top image. The primary is overexposed. Two secondary supernumeraries show. They are broader and more widely spaced than those inside the primary.

Far right: A colour subtraction enhancement. Two, possibly three supernumeraries. Spacing decreases farther from the main bow.

Greens and purples dominate the supernumeraries. Each is a mix of all the spectral colours.

The primary comes from rays reflected once inside raindrops.

There are always two rays that emerge at the same angle. Only at the rainbow's rim do they coincide.

Rays passing closer to the drop centre deflect inside the rainbow rim and light the sky there. Each ray is brightly coloured but the colours from millions of drops mix to white.

Two rays deflect through the same angle inside the rainbow's rim.

Not straight line rays but waves. Waves overlap. Where crests coincide there is light. Where they cancel there is darkness.

The overlap depends on angle. There are a series of bright fringes, their angle colour dependent - supernumeraries.

Supernumeraries extend to the bow centre. They get fainter and crowd ever closer together.

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Reference Atmospheric Optics

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  • "Samos Supernumerary Rainbows - OPOD". Atmospheric Optics. Accessed on March 29, 2024. https://atoptics.co.uk/blog/samos-supernumerary-rainbows-opod/.

  • "Samos Supernumerary Rainbows - OPOD". Atmospheric Optics, https://atoptics.co.uk/blog/samos-supernumerary-rainbows-opod/. Accessed 29 March, 2024

  • Samos Supernumerary Rainbows - OPOD. Atmospheric Optics. Retrieved from https://atoptics.co.uk/blog/samos-supernumerary-rainbows-opod/.