Anthelion

Anthelion is an atmospheric optical phenomenon that appears as a bright spot in the sky directly opposite the Sun. This phenomenon is part of the family of halos, which are produced by the reflection, refraction, and dispersion of light through ice crystals suspended in the atmosphere. The anthelion is visible when the observer's back is to the sun, typically appearing at the antisolar point, which is the point directly opposite the sun from the observer's perspective.

Formation

The formation of an anthelion requires specific atmospheric conditions. Ice crystals, primarily in the form of hexagonal plates or columns, are suspended in the upper levels of the troposphere. The sunlight enters one face of these ice crystals and exits through another, undergoing refraction and sometimes reflection within the crystal. This process bends the light by a minimum of 22 degrees, creating a variety of halo phenomena, including the anthelion. The exact appearance of the anthelion can vary depending on the orientation and shape of the ice crystals, as well as the altitude of the sun.

Observation

Observing an anthelion can be challenging due to its faint appearance and the need to shield the eyes from the direct sunlight. It is best seen when the sun is low on the horizon, either just after sunrise or before sunset. The anthelion appears as a faintly luminous spot, often surrounded by a halo of light or part of a larger halo structure, such as the parhelic circle. It is one of the less commonly observed atmospheric phenomena compared to rainbows or the more common 22-degree halo.

Scientific Significance

The study of anthelions and other halo phenomena contributes to our understanding of atmospheric optics and the properties of ice crystals in the atmosphere. These observations can also provide indirect information about the conditions in the upper atmosphere, including temperature and the presence of ice crystals.

Cultural Impact

Throughout history, atmospheric phenomena like the anthelion have inspired awe and been the subject of myths, folklore, and art. They serve as reminders of the natural beauty and complexity of the Earth's atmosphere.