parhelic circle
Noun: A parhelic circle is a rare atmospheric optical phenomenon appearing as a faint, white, luminous circle or halo that runs parallel to the horizon at the same altitude as the sun. It is caused by the reflection and refraction of sunlight by hexagonal plate-shaped ice crystals suspended in high-altitude cirrus or cirrostratus clouds.
The term is used specifically in meteorology, atmospheric science, and observational astronomy to describe this particular type of halo. It is a technical and scientific term. - The observer reported seeing a complete parhelic circle encircling the sky. - Parhelic circles are often accompanied by other halo phenomena like sundogs.
- Formation Mechanism: The parhelic circle is formed when sunlight enters the side faces of horizontally oriented, plate-like ice crystals and exits through another side face, resulting in a reflection. This differs from the more common 22° halo, which is caused by refraction through randomly oriented crystals.
- Parhelion (plural: Parhelia): Also known as a "sun dog" or "mock sun," a bright spot that often appears on the parhelic circle to the left, right, or both sides of the sun. While related and frequently co-occurring, a parhelion is a distinct phenomenon from the parhelic circle itself.
- Halo: A family of optical phenomena involving rings or arcs of light around the sun or moon. The parhelic circle is one specific type of halo.
- Atmospheric Optics: The broader scientific field studying light phenomena in the atmosphere, including halos, rainbows, and mirages.
- Sun path: A less common and less precise synonym, sometimes used in older texts or descriptively.
- Horizontal halo: A descriptive synonym referencing its orientation parallel to the horizon.
There are no common idioms or phrasal verbs associated with this specific scientific term.
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a luminous halo parallel to the horizon at the altitude of the sun; caused by ice crystals in the atmosphere
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