Antisolar halos

Last updated on September 16, 2023

Antisolar Halos: A Spectacular Atmospheric Phenomenon

Antisolar halos are a captivating atmospheric optical phenomenon that occurs at the antisolar point, which is directly opposite the sun and below the horizon during daylight hours. This unique location is the focal point for a variety of atmospheric phenomena, including glories, heiligenschein, opposition glows, the center of rainbows, the convergence of anticrepuscular rays, and the origin of shadows. In this article, we will delve into the intricacies of antisolar halos and explore their mesmerizing characteristics.

Ice Crystals and Antisolar Halos

The formation of antisolar halos is intricately linked to the presence of ice crystals in the atmosphere. These ice crystals play a crucial role in scattering sunlight and creating the stunning optical effects observed at the antisolar point. When sunlight interacts with these tiny ice crystals, it undergoes refraction, reflection, and diffraction, resulting in the formation of intricate halos around the antisolar point.

The Role of HaloSim

HaloSim, a powerful ray-tracing simulation tool, has been instrumental in understanding and visualizing the complex patterns of antisolar halos. By tracing millions of rays through virtual ice crystals, scientists and researchers have gained valuable insights into the intricate geometry and optical properties that give rise to these captivating atmospheric phenomena. HaloSim has provided a platform for studying the unique characteristics of antisolar arcs and their relationship with their anthelic point counterparts.

The Enigmatic Antisolar Arcs

One fascinating aspect of antisolar halos is the presence of antisolar arcs. These arcs are sharper and more defined compared to their anthelic point counterparts located an equal distance above the horizon. The reason behind this intriguing phenomenon is still being studied and explored by scientists. The complex interplay between ice crystal orientation, shape, and size may contribute to the distinct characteristics of antisolar arcs.

Exploring Glories at the Antisolar Point

Glories, another captivating atmospheric optical phenomenon, can also be observed at the antisolar point. These ethereal rings of colored light surround the shadow of an observer when cast on a cloud or fog bank. Glories are formed when sunlight is scattered backwards by tiny water droplets or small ice crystals in the atmosphere. The antisolar point serves as the center of these mesmerizing glories, adding to the allure of this unique atmospheric location.

Heiligenschein: A Halo around Shadows

Heiligenschein, meaning "holy light" in German, is a phenomenon closely associated with the antisolar point. It occurs when a shadow cast by an object is surrounded by a bright halo. This halo is caused by the diffraction and interference of light as it interacts with tiny water droplets or ice crystals suspended in the air. The antisolar point acts as the focal point for heiligenschein, intensifying the brilliance of this captivating optical effect.

Opposition Glows: A Miraculous Sight

Opposition glows, also known as anthelic glows, are yet another remarkable phenomenon that can be observed at the antisolar point. These glows appear as faint arcs of light that extend horizontally from the antisolar point. They are caused by the scattering and reflection of sunlight by airborne particles such as dust, pollutants, or ice crystals. The antisolar point serves as the origin and focal point for opposition glows, adding a touch of magic to the atmospheric display.

In conclusion, antisolar halos are a mesmerizing and diverse array of atmospheric optical phenomena that occur at the antisolar point. From the sharp and defined antisolar arcs to the enchanting glories, heiligenschein, and opposition glows, this unique location below the horizon offers a captivating spectacle for those fortunate enough to witness it. Through the use of advanced simulations like HaloSim, scientists continue to unravel the mysteries surrounding the formation and characteristics of antisolar halos, deepening our understanding of the complex interplay between sunlight, ice crystals, and atmospheric conditions. So, keep your eyes to the sky and marvel at the wonders that unfold at the antisolar point.

Halos at the Antisolar Point Imaged by Tom Polakis looking down on the clouds during a flight between Chicago and Phoenix. ©Tom Polakis, shown with permission.

The antisolar point is directly opposite the sun and below the horizon in daytime. It is the home of glories, the heiligenschein, opposition glows, the centre of rainbows, the focus of anticrepuscular rays and of shadows.

These rare ice halos around the aircraft's shadow were produced by Parry oriented crystals and horizontal columns. They are labelled in the 30 million ray HaloSim ray tracing at top left. Oddly enough, antisolar arcs are sharper than their anthelic point counterparts an equal distance above the horizon.

Antisolar arcs

Ice crystals

HaloSim

Glories

Heiligenschein

Opposition glows

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Reference Atmospheric Optics

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