Circumscribed Halo

Circumscribed Halo: A Rare and Breathtaking Atmospheric Phenomenon

Have you ever gazed up at the sky and been captivated by the mesmerizing display of light and color? Atmospheric optics, the study of how light interacts with the Earth's atmosphere, offers a fascinating glimpse into the hidden wonders of our natural world. One such phenomenon that never fails to astound observers is the circumscribed halo. This rare optical marvel forms a luminous ring around the sun or moon, captivating viewers with its ethereal beauty. In this article, we will delve deeper into the intricacies of the circumscribed halo, exploring its formation, characteristics, and the atmospheric conditions necessary for its occurrence.

The Formation of a Circumscribed Halo

A circumscribed halo is formed when sunlight or moonlight interacts with ice crystals suspended in the Earth's atmosphere. These ice crystals act as tiny prisms, bending and refracting light as it passes through them. When light enters an ice crystal, it undergoes multiple internal reflections before exiting, resulting in a stunning display of colors.

Characteristics of a Circumscribed Halo

The circumscribed halo is characterized by its distinct shape and vibrant colors. Unlike other halo phenomena, such as the more common 22-degree halo, the circumscribed halo appears as a bright ring encircling the sun or moon. This ring often exhibits a reddish inner edge and a bluish outer edge, with a range of colors in between. The colors are caused by the dispersion of light as it passes through the ice crystals, similar to how a prism separates white light into a rainbow spectrum.

Atmospheric Conditions Required for a Circumscribed Halo

The occurrence of a circumscribed halo depends on specific atmospheric conditions. Firstly, there must be a sufficient presence of ice crystals in the atmosphere. These ice crystals are typically found in cirrus clouds, which are composed of thin, wispy strands of ice. Secondly, the ice crystals must be oriented in a particular way. For a circumscribed halo to form, the ice crystals must be randomly oriented, meaning they are not aligned in any particular direction. This random orientation allows for the scattering and refraction of light in all directions, resulting in the halo's unique appearance.

The Role of Sun or Moon Elevation

The elevation of the sun or moon also plays a crucial role in the visibility of a circumscribed halo. When the celestial body is high in the sky, the halo may appear as a complete ring encircling it. However, when the sun or moon is lower on the horizon, the circumscribed halo can appear fragmented or incomplete. This phenomenon occurs because the light passing through the ice crystals has to travel through a larger portion of the atmosphere, increasing the chances of scattering and reducing the clarity of the halo.

Variations and Similar Optical Phenomena

While the circumscribed halo is a captivating sight on its own, variations and similar optical phenomena can add even more intrigue to the atmospheric display. One such variation is the Parry arc, a short extension that can be observed at one or both sides of the circumscribed halo. This arc is caused by plate-shaped ice crystals that are oriented differently from those creating the main halo.

Additionally, there are other atmospheric optical phenomena that share similarities with the circumscribed halo. The supralateral arc, for example, forms a horizontal arc above or below the sun or moon, intersecting with the circumscribed halo. The 46-degree halo, on the other hand, appears as a smaller ring located at a greater distance from the sun or moon compared to the circumscribed halo.

The Magic of Atmospheric Optics

The study of atmospheric optics allows us to unravel the secrets behind these enchanting natural phenomena. By understanding the intricate interactions between light and the atmosphere, we can appreciate the beauty of the world around us in a whole new light. The circumscribed halo serves as a testament to the awe-inspiring wonders that can be found within the celestial sphere. So, next time you find yourself gazing at the sky, keep an eye out for this rare and breathtaking phenomenon.

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Reference Atmospheric Optics

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  • "Circumscribed Halo". Atmospheric Optics. Accessed on March 1, 2024. https://atoptics.co.uk/blog/circumscribed-halo-3/.

  • "Circumscribed Halo". Atmospheric Optics, https://atoptics.co.uk/blog/circumscribed-halo-3/. Accessed 1 March, 2024

  • Circumscribed Halo. Atmospheric Optics. Retrieved from https://atoptics.co.uk/blog/circumscribed-halo-3/.