Comparative darkness that results from the blocking of light rays
The notions of the penumbra and umbra are important in considering eclipses (q.v.).
The umbra in the former case becomes the fully illuminated portion, and vice versa.
Each spot shows with more or less completeness a ring-shaped penumbra enclosing a darker umbra; the umbra, which looks black beside' the photosphere, is actually about as brilliant as limelight.
The umbra of a spot is generally not tormented by rapid line-of-sight motions; where any motion has been found G.
the true shadow or umbra, and also a definite boundary of the parts wholly illuminated.