An increase in the brightness of a rough surface when viewed with the source of illumination almost directly behind the observer. It arises partly because sunlight is reflected directly back out of the tiny pores in the surface. A second process, known as coherent backscattering, can contribute to the effect, as a result of multiple scattering from an irregular surface. The brilliance of the full Moon or of Mars at opposition is due to this effect, which is sometimes also known as the dry heiligenschein.
Subjects: Astronomy and Astrophysics.