If the lunar limb were to move across a bright point source of light,
observers on the Earth's surface would see bands of light race
across the ground due to diffraction; see this page for details:

http://spiff.rit.edu/richmond/occult/bessel/bessel.html

The Sun isn't a point source, of course, but in the stages of a solar
eclipse just before totality, the solar limb becomes very thin, and
finally a small set of point sources. The result can still be a set
of shadow bands.