Penumbra/pəˈnʌmbrə/ Definition 1 of 3Pro Tip 1/3Shadow Clarity Penumbra refers to a shadow's blurry part, not the darkest area. The garden was cast in a soft penumbra by the tall trees. Pro Tip 2/3Light Gradients Penumbra indicates a gradual change from light to darker shadow. The penumbra created a gentle transition from sunlight to shade. Pro Tip 3/3Eclipse Understanding During eclipses, 'penumbra' is often mentioned to describe partial shadowing. Observers outside the umbra will experience the eclipse in the penumbra.