Circumhorizon Arc, Italian Alps

Last updated on September 16, 2023

The Spectacular Circumhorizon Arc in the Italian Alps

Have you ever looked up at the sky and witnessed a breathtaking display of vibrant colors and unusual optical phenomena? One such phenomenon is the Circumhorizon Arc, a stunning atmospheric optical phenomenon that occurs in certain conditions. In this article, we will delve into the mesmerizing world of the Circumhorizon Arc as it graces the picturesque landscapes of the Italian Alps.

What is a Circumhorizon Arc?

A Circumhorizon Arc, also known as a Fire Rainbow, is an optical phenomenon that appears as a colorful band of light in the sky. It occurs when sunlight passes through ice crystals in cirrus clouds and is refracted, or bent, creating a stunning display of colors. The arc appears parallel to the horizon and can span a considerable portion of the sky, captivating anyone lucky enough to witness it.

The Conditions for a Circumhorizon Arc

To witness a Circumhorizon Arc, specific conditions must be met. Firstly, cirrus clouds, which are thin and wispy, must be present in the sky. These clouds are composed of tiny ice crystals that act as prisms, bending sunlight and creating the colorful display. Additionally, the sun must be high in the sky, at an angle of at least 58 degrees above the horizon. This requirement ensures that sunlight passes through the ice crystals at the optimal angle for refraction.

The Circumhorizon Arc in the Italian Alps

The Italian Alps provide a stunning backdrop for observing the Circumhorizon Arc. With their majestic peaks and expansive skies, this mountain range offers the perfect setting to witness this rare phenomenon. As sunlight interacts with the ice crystals in cirrus clouds above the Alps, a brilliant band of colors emerges against the backdrop of the rugged landscape.

Capturing the Beauty: Photography Tips

Photographing the Circumhorizon Arc can be a challenging yet rewarding endeavor. To capture the beauty of this phenomenon in the Italian Alps, consider the following tips:

• Use a wide-angle lens to capture the expansive sky and landscape.
• Include interesting foreground elements, such as mountains or trees, to add depth and context to your photograph.
• Experiment with different camera settings, such as exposure and white balance, to achieve the desired effect.
• Consider shooting during the golden hour, when the soft, warm light enhances the colors of the arc.
• Be patient and observant, as the Circumhorizon Arc may appear and disappear quickly.

Other Atmospheric Optics in the Italian Alps

While the Circumhorizon Arc is undoubtedly a showstopper, it is not the only atmospheric optical phenomenon that graces the Italian Alps. The region is also known for other captivating displays, including:

• Sundogs: These are bright spots that appear on either side of the sun, caused by the refraction of sunlight through ice crystals in the atmosphere.
• Halos: Circular or elliptical rings of light that encircle the sun or moon, created by the refraction and reflection of sunlight by ice crystals or water droplets.
• Cloud iridescence: This phenomenon manifests as colorful patches or bands of iridescent clouds caused by diffraction of sunlight around small water droplets or ice crystals.

The Magic of Atmospheric Optics

The world of atmospheric optics is a magical one, where light interacts with particles in the atmosphere to create awe-inspiring displays. Whether it's the vibrant colors of a Circumhorizon Arc or the ethereal glow of a halo, these phenomena remind us of the beauty and complexity of our natural world. So, next time you find yourself in the Italian Alps, don't forget to look up and marvel at the wonders that unfold above you.

Circumhorizon over the Northern Italian Alps (Valla d'Aoste) imaged by Andre Gillet

©Andre Gillet, shown with permission.

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Reference Atmospheric Optics

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