Atmospehric Halos

Last updated on September 16, 2023

Atmospheric Halos: A Stunning Display of Nature's Beauty

Atmospheric halos are a captivating phenomenon that grace our skies, ranging from the familiar circle around the sun or moon to rare and highly sought-after events where the entire sky is adorned with intricate arcs. These mesmerizing displays are created by tiny ice crystals in the atmosphere, which refract and reflect light, resulting in a delicate beauty that not only enchants us but also provides valuable insights into the crystal composition of the clouds above.

How Are Halos Formed?

The formation of halos is a result of the interaction between light and ice crystals suspended in the atmosphere. As light passes through these minuscule crystals, it undergoes refraction and reflection, leading to the creation of a variety of optical phenomena. The precise shape and characteristics of each halo are determined by the size, shape, and orientation of the ice crystals.

When light enters an ice crystal, it refracts, or bends, as it passes through the crystal's facets. This refraction causes the light to spread out and form a circle of 22 degrees around the sun or moon. This circular halo is one of the most commonly observed halos and is known as a "22° halo."

The Multitude of Halo Variations

While the 22° halo is frequently seen, atmospheric halos offer a wide array of stunning variations that can adorn our skies under specific conditions. These include:

• Sundogs: Also known as parhelia, sundogs appear as bright spots on either side of the sun. They are caused by sunlight passing through horizontally oriented ice crystals, resulting in a beautiful display of additional light sources.

• Upper Tangent Arcs: Positioned above the sun or moon, upper tangent arcs are delicate arcs that appear to touch the top of the 22° halo. These arcs form when sunlight refracts through hexagonal ice crystals with specific orientations.

• Sun Pillars: Sun pillars are vertical columns of light that extend above or below the sun. They occur when sunlight reflects off the surfaces of horizontally aligned ice crystals, creating a stunning pillar-like effect.

• Circumzenithal Arcs: Often referred to as "upside-down rainbows," circumzenithal arcs are arcs of colors that appear high in the sky. These arcs form when sunlight refracts through plate-like ice crystals, resulting in a vibrant and captivating display.

When and Where to Witness Atmospheric Halos

To witness these breathtaking displays of atmospheric halos, one must be vigilant and observant of the right conditions. Here are some key points to keep in mind:

• Cold Weather: Atmospheric halos are more likely to occur in cold weather, when ice crystals are abundant in the air. Therefore, winter months offer a higher chance of witnessing these ethereal phenomena.

• Thin, High Clouds: Halos are most commonly formed in thin, high-altitude clouds composed of ice crystals. Keep an eye out for cirrus clouds, which often provide the ideal conditions for halo formation.

• Low Sun or Moon: The best time to observe atmospheric halos is when the sun or moon is low on the horizon. This positioning allows the light to pass through a greater distance of the atmosphere, increasing the chances of encountering these captivating displays.

Exploring Halos with HaloSim

For those eager to delve deeper into the world of atmospheric halos, a fascinating tool called HaloSim provides a captivating experience. HaloSim is a full-color simulator program that allows users to create their own halo displays, offering a glimpse into the intricate interplay between light and ice crystals. By manipulating various parameters such as crystal shape and size, users can explore the vast range of possibilities and gain a deeper understanding of these natural wonders.

In conclusion, atmospheric halos are a testament to the beauty and complexity of nature. From the familiar 22° halo to the rare and intricate web of arcs that can adorn the entire sky, these optical phenomena continue to captivate our imagination. By understanding the formation process and knowing when and where to look, we can increase our chances of witnessing these awe-inspiring displays. So keep your eyes on the sky, embrace the wonder of atmospheric halos, and let nature's artistry leave you in awe.

Ice halo displays range from the familiar circle around the sun or moon to rare and prized events when the whole sky is webbed by intricate arcs.

Tiny ice crystals in the atmosphere create halos by refracting and reflecting light.

Halos bestow a delicate beauty to the skies and tell us about the crystals inhabiting the clouds.

Find out how halos are formed, when and where to see them in the skies.

Create your own halo displays by downloading the full colour simulator program, HaloSim.

A circular 22° halo surrounds a low sun. To the left and right are sundogs. Above shines an upper tangent arc and beneath is a sun pillar. HaloSim simulation of halos frequently visible in the sky.

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Reference Atmospheric Optics

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