Antarctica Halo - OPOD

Last updated on September 16, 2023

Antarctica Halo - A Stunning Phenomenon in the Snowy Landscape

The mesmerizing beauty of Antarctica never fails to amaze us, and its atmospheric optics are no exception. In this captivating scene captured by LI Hang at Zhongshan Station in Antarctica, we are treated to a rare sight - a magnificent Moon Halo illuminating the snowy surroundings. Hang shares his experience, stating, "I was kind of upset when the rarely seen 'blue moon' hid behind the clouds and it started to snow. Some minutes later I walked out the door and was astonished to see such a fantastic Moon Halo in the snow above my head."

The enchanting halo is not created by the intricate and imperfect snowflakes themselves but by simpler objects known as tumbling clusters of hexagonal prisms. These prisms, larger than 50 microns, play a crucial role in the formation of the halo. As rays of light pass through two inclined side faces of the prism, which are inclined at 60°, they create a stunning optical effect.

Contrary to popular belief, the halo is not simply a "22° ring." While it does exhibit a bright inner edge within a 22° radius, its presence can be observed well beyond this limit. In fact, in theory, the halo can stretch out to an impressive 50°. To further understand this phenomenon, HaloSim ray tracing provides a visual representation of individual colored rays. The animation reveals that the red inner edge is a result of rays refracted through a minimum deviation angle, while other rays undergo varying degrees of deflection.

The inner region of the halo is composed of rays that directly reflect off the external crystal faces. These reflections create a captivating display of light. In contrast, a filtered simulation shows only rays that pass through two side faces, providing us with what can be considered as the "pure" 22° halo.

In one of the images, a flash is used to illuminate the snowflakes, adding an extra layer of enchantment to the scene. However, even without the flash, the beauty of the halo remains undiminished, emphasizing its ethereal nature.

While the Antarctic landscape is renowned for its icy vastness, it is also a playground for optical phenomena. The combination of pristine snow and the presence of hexagonal prisms creates the perfect conditions for the formation of this breathtaking halo. It serves as a reminder of the intricate interplay between light and ice crystals in our atmosphere.

The rarity and splendor of the Antarctica Halo make it a sight to behold. As we continue to explore and study the atmospheric optics of this remote region, we gain a deeper appreciation for the wonders that nature has to offer. LI Hang's remarkable photograph not only captures a stunning moment but also invites us to marvel at the harmonious dance of light and ice in one of the most extraordinary places on Earth.

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Antarctica Lunar Halo & Snow ~ LI Hang imaged this scene on 30th July at Zhongshan Station (Chinese Permanent Station in Antarctica), Larsemann Hills. “I was kind of upset when the rarely seen "blue moon" hid behind the clouds and it started to snow. Some minutes later I walked out the door and was astonished to see such a fantastic Moon Halo in the snow above my head.” Images ©LI Hang, shown with permission

The snowflakes were not responsible for the 22° halo – they are too complicated and optically imperfect. The halo comes from simpler objects, probably tumbling clusters of hexagonal prisms larger than 50 micron. Rays cross two prism side faces inclined 60°.

The halo is often wrongly described as a ‘22° ring’. This image clearly shows halo light well outside the inner 22° radius edge. In theory it stretches out to 50°. The bright inner edge is from rays refracted through a minimum deviation angle but other rays deflect more as this animation shows.

At right a HaloSim ray tracing shows individual coloured rays. The red inner edge shows up. Beyond the inner rim are all colours which our eyes blend together as white.

The rays inside the halo are from direct external reflections off crystal faces. At far right a filtered simulation shows only rays passing through two side faces. That is the ‘pure’ 22° halo.

A flash lit the snowflakes in the top image. Here is the scene sans flash.

Note: this article has been automatically converted from the old site and may not appear as intended. You can find the original article here.

Reference Atmospheric Optics

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