Heiligenschein

Heiligenschein is a bright halo around an observer’s shadow, caused by sunlight returning toward its source after reflection from dew-covered ground or other small reflectors.

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Retroreflection: Retroreflection sends incident light back toward its source, largely independent of the angle of incidence. The halo forms because droplets and surface structures send light back toward the Sun and observer.
Glory (optics): A glory is a set of colored rings around the antisolar point, produced by light interacting with water droplets. A glory is atmospheric and colored; Heiligenschein is a ground-level halo usually lacking distinct rings.
Photometry (astronomy): Astronomical photometry measures the brightness of celestial objects and surfaces across wavelengths. Brightness changes near the antisolar point help characterize reflective planetary surfaces.
Alexander von Humboldt: Alexander von Humboldt was a Prussian naturalist and explorer whose work helped establish physical geography. Humboldt described the bright appearance around a mountain observer’s shadow and popularized the phenomenon.
Dewdrop: A dewdrop is a small bead of liquid water condensed on a surface. Dew droplets can focus and return sunlight around the antisolar point.
Brocken spectre: A Brocken spectre is an enlarged shadow of an observer projected onto clouds or fog, often surrounded by a glory. It can accompany a similar viewing geometry, but its central feature is a magnified shadow.
Lunar opposition surge: The lunar opposition surge is the Moon’s rapid brightening near full phase as it approaches opposition. It shares shadow hiding and retroreflection mechanisms with Heiligenschein on particulate surfaces.
Antisolar point: The antisolar point is the point in the sky directly opposite the Sun from an observer’s perspective. The Heiligenschein is centered near this point, where the observer’s shadow appears.
Backscattering: Backscattering is the redirection of waves or particles into directions close to their incoming direction. Light scattered backward by droplets and rough surfaces contributes to the bright region.
Antheion: An antheion is a rare atmospheric bright spot opposite the Sun, associated with ice-crystal scattering. Both appear opposite the Sun, but an antheion forms in the atmosphere rather than on reflective ground.