Heiligenschein is the technical name for the
halo of light that appears around your
shadow's head on dewy grass. It is caused by dewdrops suspended upon the
grass's hairs that focus
sunlight on the leaves, then magnify its reflection. The effect is of a halo because where the brightest spot (a reflection of the
sun) would be, the shadow of your
head is instead -- necessarily, as it's your eyes that are the end-point of the reflected light. Early morning after dawn is the only time one can see heiligenschein in action, because it's the only time when both the
sun and the
dew are out.
As a fun fact, Benvenuto Cellini was the first to write down anything about heiligenschein, and mentioned it in his 1562 memoirs. He -- being more a goldsmith and sculptor than an optician -- had the idea that the halo was a sign of his presence in God's grace. Heiligenschein translates as something like "holy brightness," although babelfish translates it as "holy banknote," an immediately hilarious concept.
Sylvanshine is a related -- and interesting -- optical effect due to dew, and it is much more recent (20th century) discovery.