Forward scatter in the context of Cassini–Huygens

In physics, backscatter (or backscattering) is the reflection of waves, particles, or signals back to the direction from which they came. It is usually a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror, although specular backscattering can occur at normal incidence with a surface. Backscattering has important applications in astronomy, photography, and medical ultrasonography. The opposite effect is forward scatter, e.g. when a translucent material like a cloud diffuses sunlight, giving soft light.

A lens flare happens when light is scattered, or flared, in a lens system, often in response to a bright light, producing a sometimes undesirable artifact in the image. This happens through light scattered by the imaging mechanism itself, for example through internal reflection and forward scatter from material imperfections in the lens. Lenses with large numbers of elements such as zooms tend to have more lens flare, as they contain a relatively large number of interfaces at which internal scattering may occur. These mechanisms differ from the focused image generation mechanism, which depends on rays from the refraction of light from the subject itself.

There are two types of flare: visible artifacts and glare across the image. The glare makes the image look "washed out" by reducing contrast and color saturation (adding light to dark image regions, and adding white to saturated regions, reducing their saturation). Visible artifacts, usually in the shape of the aperture made by the iris diaphragm, are formed when light follows a pathway through the lens that contains one or more reflections from the lens surfaces.

Anticrepuscular rays, or antisolar rays, are meteorological optical phenomena similar to crepuscular rays, but appear opposite the Sun in the sky. Anticrepuscular rays are essentially parallel, but appear to converge toward the antisolar point, the vanishing point, due to a visual illusion from linear perspective.

Anticrepuscular rays are most frequently visible around dawn or dusk. This is because the atmospheric light scattering that makes them visible (backscattering) is larger for low angles to the horizon than most other angles. Anticrepuscular rays are dimmer than crepuscular rays because backscattering is less than forward scattering.