OPOD - Rings

OPOD - Rings: A Closer Look at Atmospheric Optics

Have you ever looked up at the sky and noticed mysterious rings of light encircling the sun or moon? These captivating optical phenomena are known as "rings" or "halos," and they occur due to a combination of mirrors, reflections, and scattering of light. In this article, we will delve deeper into the science behind these mesmerizing atmospheric optics and explore the two main types of rings observed: light rings and coronas.

Light Rings: Mirrors and Reflections

When sunlight passes through a forest canopy, it encounters numerous twigs and branches. Some of these natural elements act as mirrors, reflecting the sunlight towards our eyes. The branches that are roughly perpendicular to the sun's rays produce individual glints of light. Our brain, always searching for patterns, merges these glints into circles, creating what we perceive as "light rings." Dry branches are capable of reflecting light well, especially at glancing angles, while wet branches can form even brighter rings.

The phenomenon of light rings is based on the principles of reflection. Light is only reflected from surfaces that are large, smooth, and continuous compared to the wavelengths of light. The rougher the surface, the more likely it is to scatter light rather than reflect it. Therefore, when we observe these circles of light, we are witnessing the combined effect of multiple reflections from the branches in the surrounding environment.

Coronas: Scattering and Diffraction

In addition to reflections from mirrors, another optical phenomenon known as scattering contributes to the formation of rings in the sky. Scattering occurs when individual droplets in mist or clouds disperse or scatter light in different directions. When sunlight interacts with these droplets, it undergoes a process called diffraction. Each droplet scatters waves of light, forming a circular diffraction pattern. Our eyes perceive fragments of these patterns created by each droplet and assemble them into a complete image – a corona.

A corona consists of a central white aureole surrounded by colored rings. The colors arise from the constructive and destructive interference of light waves as they interact with the droplets. The size and arrangement of the droplets determine the specific colors and the overall appearance of the corona. Capturing the intricate details of a corona requires complex mathematical simulations, which are made possible with modern computers.

Mathematical Simulations: Unlocking the Secrets of Rings

Both light rings and coronas can be mathematically simulated to understand their underlying principles. While simple geometry is sufficient to reproduce the reflections seen in light rings, the diffraction patterns responsible for coronas require intricate calculations that were once mind-numbing but are now easily achievable with modern computing power. These simulations enable scientists and researchers to gain deeper insights into the behavior of light in various atmospheric conditions.

By studying the patterns and characteristics of rings, scientists can learn more about the properties of light, the interaction of sunlight with different particles in the atmosphere, and the atmospheric conditions that give rise to these optical phenomena. The ability to simulate these phenomena not only enhances our understanding of atmospheric optics but also allows us to appreciate the beauty and complexity of nature's light displays.

In conclusion, the study of rings in atmospheric optics provides us with a fascinating glimpse into the intricate interplay between light and the natural world. Whether it's the enchanting light rings formed by reflections from twigs and branches or the captivating coronas created by the scattering and diffraction of light waves, these optical phenomena remind us of the astonishing beauty that surrounds us. So, the next time you observe rings encircling the sun or moon, take a moment to appreciate the science behind their creation and marvel at nature's captivating light show.

Rings of two kinds

Imaged by Rick Stankiewicz near Carnarvon, Halliburton County, Ontario, Canada. "... taken a day apart in the same woods. The first day that produced the light rings (left) was colder as the Sun came through the trees. The next day was foggy and as the Sun burned through it formed a corona (right)." ©Rick Stankiewicz.

Mirrors, reflections, scattering:

At left twigs and branches act as mirrors. Those happening to be roughly perpendicular to the sun reflect its light towards the eye. Our brain – forever seeking patterns – merges the individual glints into circles, ‘light rings’. The branches were dry but even so reflected light well at glancing angles. Wet branches form even brighter rings.

Light is only reflected from mirrors - large surfaces smooth and continuous compared to the wavelengths of light. Rough surfaces scatter light.

Individual droplets in mist or clouds also scatter light. At upper right the scattering forms a corona. Each individual droplet scatters waves to form a circular diffraction pattern. Our eye sees a fragment of the pattern made by each drop and reassembles a whole – a corona of central white aureole and coloured rings.

Below: Both effects can be mathematically simulated.

Simple geometry suffices to reproduce the reflections of light rings.

The diffraction of a corona requires lengthy mind numbing arithmetic only possible with modern computers that relish that sort of thing.

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Reference Atmospheric Optics

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