隐喻是人类认识世界的重要方式,是具有显著意义的认知表达,被广泛运用在各个学科之中。本文基于认知隐喻理论和形式空间化假设,分析天文学中常用的长度词“光年”的建构过程及概念内涵,尝试探讨其内在的隐喻机制。从时间域到空间域的隐喻映射赋予了“光年”度量宇宙无限空间的能力。认知隐喻的运用将抽象的宇宙距离转化为易于理解的时间和空间概念,丰富了人类对于宇宙的认知与想象。Metaphor is an important way for human beings to understand the world. It is a significant cognitive expression, which is widely used in various disciplines. Based on the theory of cognitive metaphor and the spatial hypothesis of form, this paper analyzes the construction process and conceptual connotation of the length word “light years” commonly used in astronomy, and tries to explore its internal metaphorical mechanism. Metaphorical mapping from time domain to space domain gives “light years” the ability to measure the infinite space of the universe. The use of cognitive metaphor transforms the abstract cosmic distance into easy-to-understand concepts of time and space, which enriches human’s cognition and imagination of the universe.