That part of the disk of a satellite or planet that is not illuminated as seen from Earth, usually expressed in angular measure (e.g. seconds of arc). The defect of illumination decreases as the phase increases, and vice versa.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。