Rainbows & Zero Order Glow - OPOD

Last updated on September 16, 2023

Rainbows & Zero Order Glow - Exploring the Phenomenon

Have you ever marveled at the breathtaking sight of a rainbow? The vibrant colors stretching across the sky, seemingly defying nature's limits, have captivated humans for centuries. But did you know that rainbows are not the only atmospheric optics phenomenon that can grace our skies? In this article, we will delve into the fascinating world of rainbows and explore a lesser-known spectacle known as the Zero Order Glow.

Primary & Secondary Bows: A Play of Reflections

When sunlight passes through raindrops, something magical happens. The light undergoes a series of reflections inside the spherical raindrops, resulting in the formation of primary and secondary bows. The primary bow is the more prominent of the two, with its vibrant colors spanning a wide arc across the sky. It is created by light reflecting once inside the raindrop before exiting and dispersing into its constituent colors.

The secondary bow, on the other hand, is fainter and appears as an outer arc above the primary bow. It is formed by light reflecting twice inside the raindrop before emerging. As these outgoing rays intersect, they create a bright caustic sheet, which forms the outer edge of the primary bow. Another caustic sheet forms the inner edge of the secondary bow, adding to its ethereal beauty.

The Enigmatic Zero Order Glow

While most sunlight passing through raindrops undergoes internal reflections, there are rays that pass through without any reflections at all. These rays, known as zero order rays, do not form a distant caustic sheet like their reflected counterparts. Instead, they create a captivating phenomenon known as the Zero Order Glow.

The Zero Order Glow is a stunning orange glow that suffuses the sky. Unlike rainbows, which are characterized by distinct bands of colors, this glow appears as a broad and radiant orange hue. It can often be observed in the sunward sky, adding a touch of enchantment to our surroundings. So, next time you witness something spectacular in the sky, remember to glance in the opposite direction to catch a glimpse of this mesmerizing display.

Capturing the Beauty: A Photographer's Perspective

Photographers and sky enthusiasts alike have been captivated by the allure of rainbows and the Zero Order Glow. Steinar Midtskogen, a talented photographer, captured a breathtaking 200° wide sunset panorama near Oslo, Norway. The image showcases a vivid primary rainbow on the left, with a faint outer secondary bow. Additionally, it highlights the broad orange glow of the Zero Order Glow in the sunward sky, creating a harmonious blend of colors and atmospheric phenomena.

A Visual Delight: Exploring Rainbows and the Zero Order Glow

To further immerse yourself in the world of rainbows and the Zero Order Glow, we invite you to watch the video below. This captivating footage showcases the beauty of these atmospheric optics phenomena and allows you to witness their dynamic nature firsthand. From the vibrant hues of rainbows to the radiant glow of the Zero Order Glow, the video encapsulates the awe-inspiring spectacle that can unfold in our skies.

Conclusion

Rainbows and the Zero Order Glow are just two examples of the myriad wonders that can grace our skies. The interplay of sunlight and raindrops creates a symphony of colors and ethereal glows that never cease to amaze us. Whether it's the vibrant arcs of a rainbow or the enchanting orange glow of the Zero Order Glow, these atmospheric optics phenomena remind us of the beauty and complexity of our natural world. So, next time you find yourself gazing at the sky, take a moment to appreciate the magical displays that can unfold above us.

Rays through raindrops ~ Steinar Midtskogen captured this 200° wide sunset panorama near Oslo, Norway. At left is a sunset reddened primary rainbow with a faint outer secondary. The broad orange glow in the sunward sky is, in part, the 'zero order glow' also from sun touched raindrops. See below for video.

©Steinar Midtskogen, shown with permission

Primary & secondary bows

are produced by sunlight reflecting once and twice inside near spherical raindrops.

The outgoing rays forming each bow cross one another and form a bright caustic sheet. The sheet is the outer edge of the primary bow and another sheet forms the secondary inner edge.

Zero Order Glow

Most sun rays pass through raindrops without making an internal reflection.

These rays have no minimum deviation angle and do not form a distant caustic sheet.

Instead of a rainbow there is a beautiful orange glow that suffuses the sky.

Whenever there is something spectacular in the sky check the opposite direction.

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Reference Atmospheric Optics

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