Relating to or denoting the region outside an umbra or shadow; the lighter area surrounding the darkest part of a shadow.
From Latin ex- (out of, outside) combined with umbra (shadow), plus the adjectival suffix -al. This technical term emerged in astronomy and geometry to describe light regions.
During a solar eclipse, photographers and astronomers use 'exumbral' to describe the slightly lighter ring around the darkest shadow — it's a precise way to map the geometry of shadows that matter when you're timing a total eclipse.
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