- The lighter, outer shadow of a double-shadow effect produced by a
large, unfocused source of light shining on an interfering opaque object.
A penumbral eclipse is one in which the eclipsed object
passes through the penumbral shadow.
- The lighter area, marked by radial filaments, that may surround the
darker, central umbra of a sunspot.
Penumbral waves are waves observed in the light of
H-alpha that move out from the center
of a sunspot across the penumbra.
AND OPTICAL PHENOMENA