Horizontalkreis (EE13)

The horizontal circle is a white circle of light that runs parallel to the horizon at the height of the sun. It is also referred to as a parhelic circle or sun dog circle, as the sun dogs lie on it. It is a reflection halo, which is why its color matches that of the sun. A complete horizontal circle is very rarely seen because the ice crystals must cover a large part of the sky for it.

The horizontal circle is mainly formed by the reflection of sunlight on the vertical surfaces of ice crystals. For floating plates, these are the prism surfaces, and for floating columns, the base surfaces. In addition, many other light paths are possible. One is mentioned here as an example: In plates, there is an internal reflection on the prism surface. The light enters through the upper base surface, is reflected on the prism surface, and exits through the lower base. The refraction of light upon entry and exit cancel each other out, so there is no color separation.