A what now?

A heiligenschein, also known as the opposition surge, opposition effect, or opposition spike (though some prefer to define a dew heiligenschein vs. dryheiligenschein – check out the book Rainbows, Halos and Glories by Greenler if you’re keen to learn more).

This optical effect is common on Earth and is often observed as a halo around the shadow of an observer that falls on dewy grass. This occurs when the sun is directly behind the observer, and their shadow falls on a material that has retroreflective properties (meaning that the material tends to reflect light back to its source with minimum scattering). As such, when the Sun is directly behind you on a dewy morning, you end up intercepting a very strong reflection of light from the water droplets on the grass back toward the direction of its initial source (the Sun). The appearance of a halo around your shadow is additionally amplified by the reduction in the angles of the shadows close to the anti-solar point. In this dewy-grass example, it makes the wet blades of grass look lighter and brighter closer to the anti-solar point (blocked by your shadow) because their shadows fall directly behind them close to your shadow, and thus are not able to be viewed, from your perspective.