Moondogs & Paraselenic Circle, Gloucestershire, England - OPOD

Last updated on September 16, 2023

Moondogs & Paraselenic Circle: A Spectacular Atmospheric Optics Phenomenon in Gloucestershire, England

Gloucestershire, England recently experienced a mesmerizing display of atmospheric optics known as moondogs and a paraselenic circle. These captivating phenomena were observed by Marcus Price, who generously shared his stunning images with us. The moondogs exhibited vibrant colors, which were even visible to the naked eye. Additionally, there was a faint presence of a 22-degree halo and an upper tangent arc. Let's delve into the intricacies of these awe-inspiring occurrences and explore the science behind them.

Understanding Moondogs and Paraselenic Circle

Sundogs and moondogs, collectively known as paraselenae, derive their captivating colors through refraction and dispersion, similar to how light passes through a prism. In this case, the light is refracted and dispersed through ice crystals present in the atmosphere, creating a spectacle for onlookers. The moondogs observed in Gloucestershire displayed a range of hues, which were caused by the bending and separation of light waves as they passed through the ice crystals.

The Role of Ice Crystals

The presence of ice crystals in the atmosphere is crucial for the formation of moondogs and other related optical phenomena. These ice crystals act as tiny prisms, refracting and dispersing light in various directions. The specific shape of the ice crystals influences the pattern and intensity of the colors observed. Plate-shaped ice crystals are primarily responsible for producing moondogs, as they refract and disperse light at a minimum deviation angle of 22 degrees.

Color Overlap and Subdued Hues

Due to the nature of refraction and dispersion, moondogs are never spectrally pure and exhibit overlapping colors. Shorter wavelength colors, such as blues and violets, tend to overlap with longer wavelength colors like reds, resulting in a subdued appearance. The vibrant hues observed in the moondogs photographed in Gloucestershire are a testament to this phenomenon. The overlapping and mixing of colors create a mesmerizing display that enchants observers.

Additional Atmospheric Optics Phenomena

In addition to the moondogs, Marcus Price's photographs also captured a hint of a 22-degree halo and an upper tangent arc. The 22-degree halo is a circular halo that forms around the sun or moon when light is refracted and reflected by ice crystals at a specific angle. The upper tangent arc, on the other hand, appears as a faint arc just above the 22-degree halo. These optical phenomena add an extra layer of beauty and complexity to the already captivating display.

The Unpredictability of Atmospheric Optics

Atmospheric optics phenomena, including moondogs and paraselenic circles, are notoriously unpredictable. They occur when specific atmospheric conditions align, such as the presence of ice crystals and the angle of sunlight or moonlight. As a result, capturing these phenomena requires both luck and vigilance. Marcus Price's ability to witness and photograph such a remarkable display is a testament to his dedication and the unpredictable nature of atmospheric optics.

Appreciating the Beauty of Moondogs and Paraselenic Circle

The moondogs and paraselenic circle observed in Gloucestershire serve as a reminder of the wonders that can occur in our atmosphere. These ethereal displays not only captivate our senses but also provide valuable insights into the behavior of light and the intricate workings of our atmosphere. By appreciating and studying these phenomena, we can deepen our understanding of the natural world and its many marvels.

Conclusion

The moondogs and paraselenic circle witnessed in Gloucestershire, England, were truly awe-inspiring. Marcus Price's photographs captured the vibrant colors and intricate patterns created by the refraction and dispersion of light through ice crystals in the atmosphere. These phenomena serve as a reminder of the beauty and complexity of our natural world. By studying and appreciating atmospheric optics, we can gain a deeper understanding of the mechanisms that shape our environment and the wonders that surround us.

Paraselenae & Paraselenic circle - Sighted in Gloucestershire, England by Marcus Price. The moondogs were strongly coloured (see lower image) with their hues visible by eye. There is a hint of a 22 degree halo and upper tangent arc. Images ©Marcus Price, shown with permission

Sundog/moondog colours arise from refraction and dispersion through what is effectively a 60° prism. 22° is a minimum deviation angle when the ray in the plate crystal is parallel to the intermediate side face. Other rays - as shown - are possible.

The result is colour overlap and sundogs/moondogs are never spectrally pure. Colours of shorter wavelength than reds overlap and become subdued.

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Reference Atmospheric Optics

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