Field record · optical

Rainbow arc

A primary rainbow appears opposite the Sun when suitable droplets are present; the arc is observer-dependent rather than a fixed object in one place.

factscale · viewerstructure · arc

How it forms

Sunlight entering water droplets is refracted, internally reflected and dispersed before reaching the observer, so rainbow visibility depends on illumination, droplets and viewing geometry.

What separates it from a neighbor

A rainbow uses water droplets and viewer geometry; a 22° halo is centered on the Sun or Moon and is produced by ice crystals.

Representation boundary

Keep the viewer/light geometry explicit. Avoid placing a rainbow arbitrarily relative to the Sun in explanatory diagrams.

Evidence boundary. This page separates a sourced formation explanation from the editorial “visual character” phrase above. A single image or casual observation may not contain enough context to classify a real phenomenon confidently.

Sources used for this record

NOAA NESDIS — What Causes a Rainbow?government education

Viewer-dependent rainbow geometry and light interaction with droplets.

Open source ↗

WMO International Cloud Atlas — Photometeorsinstitutional standard

Optical phenomena formed by reflection, refraction, diffraction or interference.

Open source ↗

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