Description: 光年是一个长度单位，在天文学中有时用来表示极远的天文距离，如恒星之间或星系之间的距离。它的定义是光在真空中传播一年所行进的距离：9.46万亿千米，即9.5×10¹²千米。使用“光年”这个单位后，极远的距离在数字上就变得更容易处理了：距离太阳最近的恒星有40万亿千米，更简单地说就是4.25光年。天文学家还使用“光分”以及“光时”这两个单位：光从太阳出发，到达地球大约需要8分钟，到达海王星大约需要4小时。“光年”这个术语在天文学研究中实际上很少使用，因为天文学家更倾向于使用“秒差距”（约 3.26 光年）来衡量距离。

Related Terms:

• Parsec

Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher
The translation of this term and its definition is still awaiting approval

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