Zero Order Glow, Delft, Netherlands - OPOD

Last updated on September 16, 2023

Zero Order Glow: Exploring a Spectacular Atmospheric Phenomenon in Delft, Netherlands

Delft, a charming city nestled in the Netherlands, is known for its picturesque canals and historic architecture. However, on a particular evening captured by Frank Nieuwenhuys, a captivating atmospheric spectacle unfolded in the sky above. As the sun had already set at sea level, an intense and beautiful orange-red glow emerged, resembling a distant inferno. This remarkable phenomenon, known as the Zero Order Glow, mesmerized both observers and photographers alike.

Unveiling the Enigma of the Zero Order Glow

The captivating Zero Order Glow observed in Delft on that fateful evening was a result of a unique combination of weather conditions and sunlight interaction with raindrops. While the sun had already dipped below the horizon at ground level, it continued to illuminate higher altitude clouds and air, creating a twilight glow. However, the intense light witnessed in Delft that evening was distinct from the usual twilight glow. This phenomenon has come to be known as the Zero Order Glow, a term coined by Frank Nieuwenhuys over a decade ago.

The Science Behind the Zero Order Glow

The Zero Order Glow occurs when sunlight interacts with raindrops falling in the western sky. As sunlight passes through raindrops, it undergoes refraction, causing the rays to splay out over a wide angle. These rays, heavily reddened due to the sun shining through a significant amount of atmosphere, illuminate the western sky with an intense and diffuse glow. Unlike a rainbow, where light rays converge and form an arc, the Zero Order Glow spreads through 180 degrees without concentrating in any particular direction.

Exploring the Rainbow Family

To understand the Zero Order Glow more comprehensively, let's delve into the various components of the rainbow family:

1. Primary Rainbow: A small fraction of sunlight entering a raindrop reflects off the far side and emerges towards the sun, forming the primary or 1st order rainbow.
2. Secondary Rainbow: An even smaller fraction of sunlight reflects twice within the raindrop, resulting in the formation of the 2nd order or secondary rainbow.

The Unique Characteristics of the Zero Order Glow

While the Zero Order Glow shares its origin with rainbows, it possesses distinctive characteristics that set it apart:

1. Absence of an Arc: Unlike rainbows that form distinct arcs, the Zero Order Glow does not gather or cross to create a rainbow shape. Instead, it manifests as a diffuse glow encompassing the sky.
2. Diffusion of Rays: The zero order rays spread through 180 degrees without concentrating in any specific direction. This diffusion gives rise to the captivating glow observed during this atmospheric phenomenon.

Capturing the Zero Order Glow

Frank Nieuwenhuys was fortunate enough to witness and photograph the stunning Zero Order Glow in Delft. The glow appeared at approximately 20:40, when the setting sun in the west illuminated the rear of a downpour. Recognizing the unique nature of the glow, Nieuwenhuys promptly grabbed his camera and ventured outdoors to capture the breathtaking spectacle. His photographs, taken at 20:45 and 20:46, immortalize the beauty and grandeur of this atmospheric phenomenon.

Conclusion

The Zero Order Glow witnessed in Delft, Netherlands, is a testament to the mesmerizing and awe-inspiring nature of atmospheric optics. This unique phenomenon, characterized by an intense orange-red glow in the sky, occurs when sunlight interacts with raindrops falling in the western sky. While it shares its origin with rainbows, the Zero Order Glow distinguishes itself through its diffuse nature and absence of a concentrated arc. Frank Nieuwenhuys' photographs serve as a reminder of the wonders that unfold above us, inviting us to marvel at the mysteries of our atmospheric canvas. So, the next time you spot a rainbow and the sun hangs low, don't forget to turn your gaze sunwards to catch a glimpse of the captivating Zero Order Glow.

Zero Order Glow

Frank Nieuwenhuys captured this scene at Delft in The Netherlands when the sun had already set at sea level (Delft is actually slightly below sea level).

"On August 26th) evening, between about 20:15 and 20:45 C.E.S.T. a line of heavy showers with strong wind gusts and a thunderstorm was raging over Delft.

At about 20:30 it was already pretty dark outdoors. Indoors all the lights were switched on. At about 20:40 something very surprising appeared in the sky An intense beautiful, bright but ominous-looking orange-red glow emerged, as if a giant inferno was going on in the distance.

Immediately, I understood the cause of the 'inferno-look-alike glow'. The setting sun in the west was shining on the rear of the downpour. I grabbed the camera and rushed outdoors. At 20:45 and 20:46, I made the attached pictures.

The sun was 0.3° below the horizon.

In an extraordinary way. I was lucky, I noticed the glow just in time, to rush outdoors and take the pics."

Images ©Frank Nieuwenhuys, shown with permission

At Delft the sun was already below the horizon at ground level. However, an already set sun lights higher altitude clouds and air to give a twilight glow.

But this intense light was very likely something different - A "Zero Order Glow". It's an 'unofficial' term, I coined it more than a decade ago and it seems to have stuck!

Rain was likely falling in the west. When sunlight falls on a raindrop, most of it emerges from the other side. The curved surfaces refract the light and the leaving rays splay out over a wide angle. These rays - highly reddened as the sun is shining through much atmosphere - lit up the western sky with an intense diffuse glow.

A small fraction of rays entering a drop reflect instead off the far side and emerge towards the sun. These rays form the primary or 1st order rainbow.

An even smaller fraction reflect twice to form the 2nd order or secondary rainbow.

Why "Zero order glow" and not "Zero order rainbow"? The zero order rays spread through 180° without concentrating in any direction. They do not gather or cross to form a rainbow. We see a diffuse glow in the sky and not an arc.

When you see a rainbow and the sun is low, look sunwards for the glow!

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Reference Atmospheric Optics

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