Shadow Hiding - Eric Bergman took this view in the Spring Mountains near Las Vegas, Nevada, USA. The area above the tip of the mountain shadow has no tree shadows and therefore appears brighter than the rest of the treescape. This is an 'opposition glow/effect'.   ©Eric Bergman, shown with permission.

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Shadows directly opposite the sun (red area) are hidden by the tree or object casting them. The absence of visible shadow makes the area on average brighter.

Look downwards at a treescape from a mountain or airplane. Look towards the point directly opposite the sun, the antisolar point. There is a small area that appears brighter and slightly more yellow than its surroundings. It can also be spotted in fields of stubble.

The effect is most easily seen when you are moving - the brighter spot then moves with you across the landscape and the subtle contrast differences are more apparent.

This is the 'opposition effect' or 'opposition glow'. One** cause is shadow hiding. At the antisolar point shadows are hidden beneath the objects casting them. Farther away the shadows become less and less hidden. The shadows progressively appear on the side of the object nearest the antisolar point.

The antisolar point area has fewer visible shadows and thus appears brighter. There is another effect. Shadows are bluish because they are lit mostly by blue sky. The absence of blue shadows at the antisolar point renders that area more yellow.

**One cause is shadow hiding. There are others. Retroreflection in rock minerals and an effect called coherent backscatter also contribute. If there is dew then the heiligenschein also brightens the area.