Seasons and sky
Circumzenithal Arc
Direct answer
Circumzenithal Arc: A Circumzenithal Arc is a bright, strongly colored ice-crystal arc high above the Sun and curved around the zenith.
A Circumzenithal Arc is an upside-down rainbow-like halo high in the sky.
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At a glance
- Found in
- Seasons & Earth Almanac
- Related
- Sundog, Glory, Astronomical Season, Equinox
A Circumzenithal Arc is an upside-down rainbow-like halo high in the sky.
A Sun-Earth orientation for seasonal, atmospheric, tidal, and terrestrial terms.
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The story behind Circumzenithal Arc
Ray-path analysis showed that sunlight enters the top face and exits a side face of horizontally oriented hexagonal plates.
Why Circumzenithal Arc matters
Circumzenithal Arc’s vivid spectral separation and high position make it one of the most distinctive plate-crystal halo forms.
How to read Circumzenithal Arc
Circumzenithal Arc in halo guides applies when the Sun is low enough and cirrus plate crystals are present.
Circumzenithal Arc in practice: an example
The arc can appear above a 22-degree halo when the Sun is below roughly 32 degrees altitude.
Where readings of Circumzenithal Arc go wrong
It is a mistake to call every overhead rainbow fragment a Circumzenithal Arc; check its orientation relative to the Sun.
Sources and editorial method
Research references used for this entry include:
- National Weather Service: Atmospheric Optics - NWS science reference for halos, pillars, sundogs, green flashes, rays, and related optical displays.
- Source
- The Great Almanac Dictionary
- Category
- Seasons & Earth Almanac
- Last updated
- 2026-09-26
Check high above the low Sun
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Common questions
What is a Circumzenithal Arc?
A Circumzenithal Arc is a bright, strongly colored ice-crystal arc high above the Sun and curved around the zenith.
What do people get wrong about a Circumzenithal Arc?
It is a mistake to call every overhead rainbow fragment a Circumzenithal Arc; check its orientation relative to the Sun.
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