umbra
umbra
Noun
pl: umbrae
This term describes the absolute center of a shadow where the light source is entirely obscured. It carries a clinical, scientific connotation, typically appearing in astronomical or optical contexts to distinguish the total darkness from the penumbra, which is the lighter, partial shadow surrounding it.
In solar physics, the word specifically identifies the cool, dark core of a sunspot. Because it refers to a specific geometric or physical region of a shadow, it is used in technical descriptions of eclipses and celestial alignments rather than in casual descriptions of shade.