The amount of material in an imaginary cylinder (usually of cross-sectional area 1 cm2) between an observer and an astronomical object. Column densities in our Galaxy are usually in the range 1019–1023 atoms/cm2.
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。