AI Insight
A circumhorizontal arc, informally called a "fire rainbow," was photographed over West Virginia in 2021. This optical phenomenon occurs when sunlight refracts through horizontally-aligned, flat hexagonal ice crystals in cirrus clouds, creating a flame-like appearance parallel to the horizon. The effect requires the Sun to be at least 58 degrees above the horizon and the presence of specific cirrus cloud types with properly oriented ice crystals, making these arcs relatively rare to observe.
Why it matters
This phenomenon demonstrates atmospheric optics principles and the precise conditions required for specific optical effects in Earth's atmosphere. Understanding such events helps meteorologists and atmospheric scientists better comprehend ice crystal formation, cloud physics, and light-matter interactions in the upper atmosphere.
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APOD
Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
A Fire Rainbow over West Virginia
Explanation: What’s happening to this cloud? Ice crystals in a distant cirrus cloud are acting like little floating prisms. Known informally as a fire rainbow for its flame-like appearance, a circumhorizon arc appears parallel to the horizon. For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds present below — in this case cirrus fibratus. The numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner. Therefore, circumhorizontal arcs are somewhat unusual to see. The featured fire rainbow was photographed in 2021 near North Fork Mountain in West Virginia, USA.
Tomorrow’s picture: meteoric photobomb
| Date: | August 2, 2026 |
|---|---|
| Credit & Copyright: | Christa Harbig |
| Authors & editors: | Robert Nemiroff, Jerry Bonnell, Cecilia Chirenti, Keighley Rockcliffe |
| A service of: |
ASD at NASA / GSFC, NASA Science Activation & Michigan Tech. U. |
Source: APOD: 2026 August 2 – A Fire Rainbow over West Virginia