What can spark the appearance of Baily's Beads?

As the moon "grazes" by the Sun during a solar eclipse, the rugged lunar topography allows beads of sunlight to shine through.
This effect is called "Baily's Beads" named in honor of Francis Baily who first noted the phenomena in 1836.

http://sunearth.gsfc.nasa.gov/eclipse/TSE98reports/TSE98Nugent.html

(Dang! There's a name for everything, isn't there? )