Penumbra
a faint shadow thrown by a luminous body. It is brighter than the true shadow, though less so than the luminous body itself. It is a modification of the true shadow produced by the commingling with it of rays emitted by a portion of the luminous body. In an eclipse of the moon, the rays which have just grazed the edge of the earth are bent inward by the refraction of the atmosphere, besides having become tinged with a ruddy or copper hue. Falling on the moon, then in shadow, they often render it faintly visible, and though of a copper hue, yet bright enough to permit markings on its surface to be seen. Yet at this time the moon is so much behind the earth that it cannot be reached by any direct rays from the sun. In an eclipse the periods when the first and the last contact with the penumbra will take place are always carefully noted.