Examples of Opposition Effect (installation view) - 2015
Lunar soil has an open structure with many areas of deep shadow. When looking in a direction directly away from the sun, shadows are hidden by the object casting them. The anti solar point and the adjacent areas therefore appear brighter than elsewhere because they have more sunlit surfaces and less shadow. This phenomenon is useful in determining position relative to the object, though there are other factors that contribute to the glow. The opposition effect was so named because it is substantially responsible for the brightness of the Moon and Mars at opposition, i.e. when they are near the anti solar point in our sky.