Zero Order Glow - Rainbows

Last updated on September 16, 2023

Zero Order Glow - Rainbows: Exploring the Intense Glow in the Sunward Sky

Rainstorms have an ethereal beauty that captivates our senses. As rain falls from the heavens, it interacts with sunlight, creating a mesmerizing display of atmospheric optics. One such phenomenon is the zero order glow, a radiant glow that illuminates the sunward part of the sky during rain showers. In this article, we will delve into the intricacies of this enchanting spectacle and uncover the science behind it.

When light enters raindrops, most of it passes through without undergoing any internal reflection. This light then converges to form an intense glow in the sunward region of the sky. This phenomenon can be observed whenever rain falls in that particular direction. Imagine standing outside during a rainstorm, witnessing the celestial canvas come alive with vibrant colors.

As the zero order glow rays enter and exit the raindrops, they disperse into a beautiful array of colors. The light bends and separates into its constituent wavelengths, creating a spectrum of hues. However, unlike a traditional rainbow, there is no turning point or minimum deflection angle for these dispersed colors. Consequently, all the colors overlap again, resulting in a stunning blend of hues that dance across the sky.

The zero order glow is a captivating visual spectacle, but its scientific explanation lies in the principles of optics. When sunlight enters a raindrop, it refracts, or bends, as it transitions from air to water. This bending occurs due to the difference in the speed of light in these two mediums. The light then undergoes multiple internal reflections within the raindrop before exiting back into the air.

During these internal reflections, the light separates into its component colors due to the phenomenon of dispersion. Each color has a specific wavelength and refracts at a slightly different angle. As a result, the dispersed colors fan out and create the familiar spectrum we associate with rainbows. However, in the case of the zero order glow, these dispersed colors overlap again, creating a unique and captivating visual effect.

The intensity of the zero order glow depends on various factors, such as the size and shape of the raindrops. Larger raindrops tend to produce a more pronounced glow, while smaller drops may yield a fainter display. Additionally, the angle at which the sunlight enters the raindrops also influences the intensity of the glow. These factors combine to create a diverse range of zero order glow experiences, each with its own unique charm.

It is important to note that capturing the zero order glow in photographs can be challenging. The camera's position relative to the sun plays a crucial role in determining whether the glow will be visible or not. If the camera is pointing directly towards the sun, the intense glow may not be captured in the image. This is why, in certain photographs, the absence of a traditional rainbow can be observed.

In conclusion, the zero order glow is a captivating atmospheric optics phenomenon that occurs during rainstorms. It is characterized by an intense glow in the sunward part of the sky, formed by light passing through raindrops without internal reflection. The dispersed colors of this glow overlap again, creating a mesmerizing blend of hues. Understanding the science behind this spectacle allows us to appreciate the beauty and complexity of our natural world. So, next time you find yourself caught in a rainstorm, take a moment to look up and marvel at the enchanting display of the zero order glow.

Darko Podravec imaged this beautiful sky during an early evening rainstorm at Bjelovar, Croatia.

There is no bow because the camera is pointing sunward.

Most of the light entering raindrops passes through them without any internal reflection. This light forms an intense glow in the sunward part of the sky. Look for it whenever rain falls there.

These zero order glow rays are dispersed into colours as they enter and leave the raindrops. However, there is no turning point or minimum deflection angle and so all the colours overlap again.

Image ©Darko Podravec, shown with permission.

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Reference Atmospheric Optics

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