Fogbow, Glory & Brocken Spectre

Last updated on September 16, 2023

Fogbow, Glory & Brocken Spectre: Exploring the Phenomena of Atmospheric Optics

Atmospheric optics never ceases to amaze us with its captivating displays of natural phenomena. Among these enchanting spectacles are the fogbow, glory, and Brocken spectre. These optical marvels occur when sunlight interacts with mist or fog, creating breathtaking visual experiences in the sky.

The Fogbow: A Subtle and Mysterious Rainbow

When the sun's rays penetrate through mist or fog, a fogbow may grace the sky. Similar to a rainbow, a fogbow forms a circular arc, but its colors are much fainter and less vibrant. The outermost ring of the fogbow appears almost colorless, resembling the primary rainbow. However, upon closer inspection, at least four additional supernumerary fringes can be observed within the fogbow, displaying more intense hues.

The formation of fogbows is closely linked to the phenomenon of light scattering and diffraction by minuscule water droplets. As these droplets disperse sunlight, diffraction becomes more pronounced when their size approaches the wavelength of light. Consequently, the fogbow's ethereal beauty emerges as the sun's rays interact with these tiny water particles suspended in the mist.

Glories: Rings of Radiant Splendor

Accompanying the fogbow in the sky, one may also witness the captivating sight of a glory. This optical phenomenon manifests as a series of concentric rings encircling the observer's shadow cast onto the mist or fog. The center of the glory aligns with the antisolar point, which is directly opposite the position of the sun.

Glories share a common origin with fogbows, arising from the scattering and diffraction of sunlight by water droplets. The intricate patterns of concentric rings in a glory result from constructive and destructive interference of light waves as they pass through these droplets. The precise conditions required for a glory to form include the presence of uniformly sized droplets and the observer's position relative to the antisolar point.

The Brocken Spectre: A Glimpse of the Enigmatic

In certain atmospheric conditions, the interplay of mist or fog, sunlight, and an observer's position can give rise to a mesmerizing phenomenon known as the Brocken spectre. Named after the Brocken, a peak in the Harz Mountains of Germany where it was first observed, this spectacle showcases a magnified shadow of the observer cast onto the mist or fog.

The Brocken spectre materializes when sunlight projects an observer's shadow onto a cloud or fog bank. The phenomenon is enhanced by the diffraction and scattering of light as it interacts with the water droplets present in the mist. The result is a larger-than-life silhouette surrounded by a radiant halo, often accompanied by colorful rings resembling a glory.

Exploring the Science Behind Atmospheric Optics

The captivating interplay of light and water droplets in fogbows, glories, and Brocken spectres showcases the intricate nature of atmospheric optics. These phenomena offer us glimpses into the fascinating world of light scattering and diffraction. By understanding the underlying scientific principles, we can unravel the mysteries behind these captivating displays in the sky.

Here are some key points to consider:

• Fogbows and glories are formed when sunlight interacts with mist or fog, resulting in diffraction and scattering of light by water droplets.
• Fogbows appear as faint, colorless rings with additional supernumerary fringes displaying more intense hues.
• Glories manifest as concentric rings encircling an observer's shadow cast onto the mist or fog, with the center aligning with the antisolar point.
• The Brocken spectre occurs when an observer's shadow is magnified and surrounded by a halo on mist or fog, often resembling a glory.
• These phenomena demonstrate the remarkable effects of diffraction and scattering as light interacts with tiny water droplets suspended in the atmosphere.
• The precise conditions required for fogbows, glories, and Brocken spectres involve factors such as droplet size, uniformity, and the observer's position relative to the sun and antisolar point.

Embracing the Wonder of Atmospheric Optics

As we gaze at the sky and witness the enchanting displays of fogbows, glories, and Brocken spectres, we are reminded of the awe-inspiring beauty that nature offers. These atmospheric phenomena serve as a testament to the intricacies of light and its interaction with our environment. By delving into the science behind these optical wonders, we gain a deeper appreciation for the mesmerizing spectacle that unfolds above us. So, the next time mist or fog blankets the landscape, keep your eyes peeled for these captivating displays of atmospheric optics.

Fogbow & Glory from a col on Piz Lad near the Italian, Swiss and Austrian borders. Imaged by Gangolf Haub (climb) September 8, '08. Image ©Gangolf Haub, shown with permission.

Gangolf’s shadow in the mist (or ‘Brocken Spectre’) is surrounded by a multi-ringed glory. Further away the much larger rings of a fogbow dominate the scene. The outer, almost colourless, ring is the fogbow primary corresponding to that of a rainbow. Inside are at least four more strongly coloured supernumerary fringes.

Fogbows and glories can be seen when the sun breaks through mist or fog. They are centered on the antisolar point directly opposite the sun.

They are part of the same phenomenon of light scattering and diffraction by tiny water droplets. The corona (next OPOD) seen around the moon or sun is generated at the same time. Diffraction becomes more marked as the scatterers shrink towards the order of size of the wavelength of light.

Diffraction is sometimes thought of as a laboratory curiosity but here it is writ large across the sky.

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